Maintaining Ni-MH C-types

My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK

 

[Rick C]

On Wednesday, February 19, 2020 at 10:36:43 AM UTC-5, terry...@gmail.com wrote:
> My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Batteries are charged when they are low on power and the charging stops when topped off. This usually requires measurements. It would be hard to do using timers for both the charge time and the time between charges unless you know exactly the power consumed. Even then eventually they would either be overcharged or under charged.


> Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I don't know that it is ok to trickle charge NiMH batteries. There are many web pages on this. What do they say?


> I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

What power do you need?


> All ideas would be much appreciated please.

Lead acid batteries can be trickle charged ok. Have you considered one of those?

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209

 

[Clive Arthur]

On 19/02/2020 15:36, terrypingm@gmail.com wrote:

My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK

Trickle charging for emergency lighting is usually around C/40. 300mA
for 16 hours is 4.8Ah, so they could be 4Ah cells, and C/40 for that is
100mA, so I'd increase the trickle. I'd put a Schottky diode across each
cell to minimise reverse charge damage should that ever happen.

--
Cheers
Clive

 

[George Herold]

On Wednesday, February 19, 2020 at 10:36:43 AM UTC-5, terry...@gmail.com wrote:

My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK

Batteries are more complicated these days.
Battery University is OK.
https://batteryuniversity.com/learn/article/nickel_based_batteries
(It says NiMH can be damaged by over charging.)

5V at 4A sounds like something a little wall wart could do.

George H.

 

[ehsjr]

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:

My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK

Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

 

[Terry Pinnell]

ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.
- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1



Terry, East Grinstead, UK

 

[Lasse Langwadt Christense]

torsdag den 20. februar 2020 kl. 18.58.39 UTC+1 skrev Terry Pinnell:

ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
https://www.odroid.co.uk/index.php?route=product/product&product_id=819

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

https://dk.rs-online.com/web/p/blybatterier/1748855/

max discharge 15A

 

[Rick C]

On Thursday, February 20, 2020 at 12:58:39 PM UTC-5, Terry Pinnell wrote:

ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

A simple diode or two could provide the voltage reduction. I have no idea why you think a lead-acid battery can't supply the current. They are used to supply hundreds of amps to start car engines! Even a small one can be used as a booster to start a car.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

When you say C-Type, do you mean C size?

Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

What is the battery voltage when running? Batteries can develop high resistance dropping the voltage under load.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.

Does the motor run ok when not connected to the curtain? Does the curtain work smoothly without the motor?

- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1

Four sets? You have four sets of batteries? For four windows?

You could reduce the size of your spindle giving the motor more leverage.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

[Terry Pinnell]

Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

torsdag den 20. februar 2020 kl. 18.58.39 UTC+1 skrev Terry Pinnell:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!


https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
https://www.odroid.co.uk/index.php?route=product/product&product_id=819


A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

https://dk.rs-online.com/web/p/blybatterier/1748855/

max discharge 15A

Thanks. I've ordered the CPC supply. Even if I decide to stay with my
batteries, that will be handy for other purposes.

Terry, East Grinstead, UK

 

[Terry Pinnell]

Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Thursday, February 20, 2020 at 12:58:39 PM UTC-5, Terry Pinnell wrote:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

A simple diode or two could provide the voltage reduction. I have no idea why you think a lead-acid battery can't supply the current. They are used to supply hundreds of amps to start car engines! Even a small one can be used as a booster to start a car.

I stand corrected. That Swedish product Lasse referenced is a good
example.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

When you say C-Type, do you mean C size?

amazon.co.uk call them C 'types'. And yes, of course, they relate to the
sizes.

Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

What is the battery voltage when running? Batteries can develop high resistance dropping the voltage under load.

Typically 3.7-3.8 V. I understand battery resistance.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.

Does the motor run ok when not connected to the curtain?

Well, it spins fast and is hard to stop by hand! But I haven't
rigorously tested its torque. Did you see this:
"...I could try a new one of identical type I still have."

>Does the curtain work smoothly without the motor?

The only way to open/close the curtain is to do so awkwardly by rotating
the spindle by finger power.

- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1

Four sets? You have four sets of batteries? For four windows?

"I now have four sets (of three C-Type NiMh), bought over the last few
years..."
I obviously need at least TWO sets, to allow for usage while one set is
being recharged. And the earlier ones naturally are no longer as
effective. Also did you read this from my opening post:
"My ancient window opener motor..." Singular.

>You could reduce the size of your spindle giving the motor more leverage.

I'd prefer to focus on restoring its previous (designed) performance. It
was at one time swishing them open in about 1.5 s. Sure don't want to
reduce its *current* slow speed. Did you read this:
"It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!"

Terry, East Grinstead, UK

 

[Rick C]

On Thursday, February 20, 2020 at 5:52:24 PM UTC-5, Terry Pinnell wrote:

Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Thursday, February 20, 2020 at 12:58:39 PM UTC-5, Terry Pinnell wrote:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

A simple diode or two could provide the voltage reduction. I have no idea why you think a lead-acid battery can't supply the current. They are used to supply hundreds of amps to start car engines! Even a small one can be used as a booster to start a car.

I stand corrected. That Swedish product Lasse referenced is a good
example.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

When you say C-Type, do you mean C size?

amazon.co.uk call them C 'types'. And yes, of course, they relate to the
sizes.



Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

What is the battery voltage when running? Batteries can develop high resistance dropping the voltage under load.

Typically 3.7-3.8 V. I understand battery resistance.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.

Does the motor run ok when not connected to the curtain?

Well, it spins fast and is hard to stop by hand! But I haven't
rigorously tested its torque. Did you see this:
"...I could try a new one of identical type I still have."

Does the curtain work smoothly without the motor?

The only way to open/close the curtain is to do so awkwardly by rotating
the spindle by finger power.

I don't know how easy it is to disengage and mechanism. This seems to be a home-brew rig and I would have provided a quick disconnect just for such testing. Elsewhere you said you provided hand assist. Was that by pulling the curtain or pulling on the cord?

- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1

Four sets? You have four sets of batteries? For four windows?

"I now have four sets (of three C-Type NiMh), bought over the last few
years..."
I obviously need at least TWO sets, to allow for usage while one set is
being recharged.

Quoting earlier text is not useful for information. I didn't see anything that indicated you disconnect the batteries to charge. My phone does not need to disconnect the one battery to charge. That seems like an inordinately clumsy way to work. In fact, if you swap two sets of batteries, where is the problem??? You should be able to charge faster in a conventional charger and always have a set ready to use by the time the set on the curtain runs down.

And the earlier ones naturally are no longer as
effective. Also did you read this from my opening post:
"My ancient window opener motor..." Singular.

Yes, is that supposed to be a hint about the batteries? Can you decode it for me?

You could reduce the size of your spindle giving the motor more leverage..

I'd prefer to focus on restoring its previous (designed) performance. It
was at one time swishing them open in about 1.5 s. Sure don't want to
reduce its *current* slow speed. Did you read this:
"It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!"

You seem to like to point out hints you've provided that I didn't pick up on as to their full meaning. If the unit is running slowly because the batteries or motor are now insufficient to the task, either because the curtain is binding slightly or because of reduced power in the drive, a change in gearing to properly match the load to the drive might allow a speedup regardless of where the problem is. It seems like a simple thing to do.

Clearly you lack some aspect of understanding the problem or you would not be asking for help. I don't know exactly what parts you understand and which you don't. So I'm shotgunning ideas. Sorry if this isn't welcome.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[david eather]

On 21/02/2020 3:58 am, Terry Pinnell wrote:

ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.
- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1



Terry, East Grinstead, UK

if changing batteries you could think about NiCds. Same voltage but more
capable of high load currents (like starting a motor) plus they are more
tolerant of trickle charging.

 

[Rick C]

On Friday, February 21, 2020 at 3:51:21 AM UTC-5, Terry Pinnell wrote:

Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Thursday, February 20, 2020 at 5:52:24 PM UTC-5, Terry Pinnell wrote:
Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Thursday, February 20, 2020 at 12:58:39 PM UTC-5, Terry Pinnell wrote:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth..

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

A simple diode or two could provide the voltage reduction. I have no idea why you think a lead-acid battery can't supply the current. They are used to supply hundreds of amps to start car engines! Even a small one can be used as a booster to start a car.

I stand corrected. That Swedish product Lasse referenced is a good
example.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

When you say C-Type, do you mean C size?

amazon.co.uk call them C 'types'. And yes, of course, they relate to the
sizes.



Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

What is the battery voltage when running? Batteries can develop high resistance dropping the voltage under load.

Typically 3.7-3.8 V. I understand battery resistance.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.

Does the motor run ok when not connected to the curtain?

Well, it spins fast and is hard to stop by hand! But I haven't
rigorously tested its torque. Did you see this:
"...I could try a new one of identical type I still have."

Does the curtain work smoothly without the motor?

The only way to open/close the curtain is to do so awkwardly by rotating
the spindle by finger power.

I don't know how easy it is to disengage and mechanism. This seems to be a home-brew rig and I would have provided a quick disconnect just for such testing. Elsewhere you said you provided hand assist. Was that by pulling the curtain or pulling on the cord?


- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1

Four sets? You have four sets of batteries? For four windows?

"I now have four sets (of three C-Type NiMh), bought over the last few
years..."
I obviously need at least TWO sets, to allow for usage while one set is
being recharged.

Quoting earlier text is not useful for information. I didn't see anything that indicated you disconnect the batteries to charge. My phone does not need to disconnect the one battery to charge. That seems like an inordinately clumsy way to work. In fact, if you swap two sets of batteries, where is the problem??? You should be able to charge faster in a conventional charger and always have a set ready to use by the time the set on the curtain runs down.


And the earlier ones naturally are no longer as
effective. Also did you read this from my opening post:
"My ancient window opener motor..." Singular.

Yes, is that supposed to be a hint about the batteries? Can you decode it for me?


You could reduce the size of your spindle giving the motor more leverage.

I'd prefer to focus on restoring its previous (designed) performance. It
was at one time swishing them open in about 1.5 s. Sure don't want to
reduce its *current* slow speed. Did you read this:
"It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!"

You seem to like to point out hints you've provided that I didn't pick up on as to their full meaning. If the unit is running slowly because the batteries or motor are now insufficient to the task, either because the curtain is binding slightly or because of reduced power in the drive, a change in gearing to properly match the load to the drive might allow a speedup regardless of where the problem is. It seems like a simple thing to do.

Clearly you lack some aspect of understanding the problem or you would not be asking for help. I don't know exactly what parts you understand and which you don't. So I'm shotgunning ideas. Sorry if this isn't welcome.

I welcome shotgun suggestions but I got the impression that you did not
bother to read my posts with any care before firing them off.

Several of your questions were answered in the subject heading and first
two sentences of my opening post. For example you now ask "I didn't see
anything that indicated you disconnect the batteries to charge." Yet at
the start I wrote: "The circuit includes a trickle current of about 35
mA but I’m still finding it necessary to recharge the batteries every
few weeks."

Terry, East Grinstead, UK

Exactly, you still think it says something it doesn't.

I'm not interested in arguing with you about this. Enjoy.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[david eather]

Trickle charging for emergency lighting is usually around C/40.  300mA
for 16 hours is 4.8Ah, so they could be 4Ah cells, and C/40 for that is
100mA, so I'd increase the trickle. I'd put a Schottky diode across each
cell to minimise reverse charge damage should that ever happen.

rather than a diode you could use a icl7660 (or compatible) set up as a
voltage divider. If one cell's voltage rises higher than the other the
7660 will shunt current from the higher voltage cell to the lower
voltage one. Most data sheets show the voltage divider application

 

[Terry Pinnell]

Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Thursday, February 20, 2020 at 5:52:24 PM UTC-5, Terry Pinnell wrote:
Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Thursday, February 20, 2020 at 12:58:39 PM UTC-5, Terry Pinnell wrote:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

A simple diode or two could provide the voltage reduction. I have no idea why you think a lead-acid battery can't supply the current. They are used to supply hundreds of amps to start car engines! Even a small one can be used as a booster to start a car.

I stand corrected. That Swedish product Lasse referenced is a good
example.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

When you say C-Type, do you mean C size?

amazon.co.uk call them C 'types'. And yes, of course, they relate to the
sizes.



Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

What is the battery voltage when running? Batteries can develop high resistance dropping the voltage under load.

Typically 3.7-3.8 V. I understand battery resistance.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.

Does the motor run ok when not connected to the curtain?

Well, it spins fast and is hard to stop by hand! But I haven't
rigorously tested its torque. Did you see this:
"...I could try a new one of identical type I still have."

Does the curtain work smoothly without the motor?

The only way to open/close the curtain is to do so awkwardly by rotating
the spindle by finger power.

I don't know how easy it is to disengage and mechanism. This seems to be a home-brew rig and I would have provided a quick disconnect just for such testing. Elsewhere you said you provided hand assist. Was that by pulling the curtain or pulling on the cord?


- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1

Four sets? You have four sets of batteries? For four windows?

"I now have four sets (of three C-Type NiMh), bought over the last few
years..."
I obviously need at least TWO sets, to allow for usage while one set is
being recharged.

Quoting earlier text is not useful for information. I didn't see anything that indicated you disconnect the batteries to charge. My phone does not need to disconnect the one battery to charge. That seems like an inordinately clumsy way to work. In fact, if you swap two sets of batteries, where is the problem??? You should be able to charge faster in a conventional charger and always have a set ready to use by the time the set on the curtain runs down.


And the earlier ones naturally are no longer as
effective. Also did you read this from my opening post:
"My ancient window opener motor..." Singular.

Yes, is that supposed to be a hint about the batteries? Can you decode it for me?


You could reduce the size of your spindle giving the motor more leverage.

I'd prefer to focus on restoring its previous (designed) performance. It
was at one time swishing them open in about 1.5 s. Sure don't want to
reduce its *current* slow speed. Did you read this:
"It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!"

You seem to like to point out hints you've provided that I didn't pick up on as to their full meaning. If the unit is running slowly because the batteries or motor are now insufficient to the task, either because the curtain is binding slightly or because of reduced power in the drive, a change in gearing to properly match the load to the drive might allow a speedup regardless of where the problem is. It seems like a simple thing to do.

Clearly you lack some aspect of understanding the problem or you would not be asking for help. I don't know exactly what parts you understand and which you don't. So I'm shotgunning ideas. Sorry if this isn't welcome.

I welcome shotgun suggestions but I got the impression that you did not
bother to read my posts with any care before firing them off.

Several of your questions were answered in the subject heading and first
two sentences of my opening post. For example you now ask "I didn't see
anything that indicated you disconnect the batteries to charge." Yet at
the start I wrote: "The circuit includes a trickle current of about 35
mA but I’m still finding it necessary to recharge the batteries every
few weeks."

Terry, East Grinstead, UK

 

[George Herold]

On Thursday, February 20, 2020 at 1:29:14 PM UTC-5, Lasse Langwadt Christensen wrote:

torsdag den 20. februar 2020 kl. 18.58.39 UTC+1 skrev Terry Pinnell:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!


https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
https://www.odroid.co.uk/index.php?route=product/product&product_id=819

Searching for parts these days I first go to Digikey to find the part
I want. (good search engine) and then go to octoparts to see who has that
part in stock. I assume octopart works in Europe.

George H.

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

https://dk.rs-online.com/web/p/blybatterier/1748855/

max discharge 15A

 

[Terry Pinnell]

david eather <eathDELETEer@tpg.com.au> wrote:

Trickle charging for emergency lighting is usually around C/40.  300mA
for 16 hours is 4.8Ah, so they could be 4Ah cells, and C/40 for that is
100mA, so I'd increase the trickle. I'd put a Schottky diode across each
cell to minimise reverse charge damage should that ever happen.


rather than a diode you could use a icl7660 (or compatible) set up as a
voltage divider. If one cell's voltage rises higher than the other the
7660 will shunt current from the higher voltage cell to the lower
voltage one. Most data sheets show the voltage divider application

Thanks, but that might be tricky to implement, as the three batteries
are in a very cramped case. My design mistake back in 2004. And to be
honest, given that this circuit has worked well in the past, I hope I
can restore performance without such complications.

It's only been a day or so since I upped the trickle charge to 50 mA,
but I'm seeing some improvement already.

Terry, East Grinstead, UK

 

[Terry Pinnell]

david eather <eathDELETEer@tpg.com.au> wrote:

On 21/02/2020 3:58 am, Terry Pinnell wrote:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.
- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1



Terry, East Grinstead, UK


if changing batteries you could think about NiCds. Same voltage but more
capable of high load currents (like starting a motor) plus they are more
tolerant of trickle charging.

Thanks, hadn't thought of that. Sort of assumed that Nicads were to
batteries rather like Betamax was to recording media.

Terry, East Grinstead, UK

 

[Lasse Langwadt Christense]

fredag den 21. februar 2020 kl. 19.30.05 UTC+1 skrev Terry Pinnell:

david eather <eathDELETEer@tpg.com.au> wrote:

On 21/02/2020 3:58 am, Terry Pinnell wrote:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.
- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1



Terry, East Grinstead, UK


if changing batteries you could think about NiCds. Same voltage but more
capable of high load currents (like starting a motor) plus they are more
tolerant of trickle charging.

Thanks, hadn't thought of that. Sort of assumed that Nicads were to
batteries rather like Betamax was to recording media.

more like leaded fuel and freon ...

 

[Tom Gardner]

On 21/02/20 18:29, Terry Pinnell wrote:

david eather <eathDELETEer@tpg.com.au> wrote:

On 21/02/2020 3:58 am, Terry Pinnell wrote:
ehsjr <ehsjr@verizon.net> wrote:

On 2/19/2020 10:36 AM, terrypingm@gmail.com wrote:
My ancient window opener motor is powered by three of the subject rechargeable batteries. The circuit includes a trickle current of about 35 mA but I’m still finding it necessary to recharge the batteries every few weeks. To ensure I always have a replacement set ready I plan a little circuit to cycle through: charge (say the recommended 300 mA for 16 hours), cut the supply, wait for N days, reapply the supply...repeating until needed. Is that a sensible approach? If so, what would be a good value for N?

Or could I achieve this more simply by increasing the trickle charge? The batteries use about 4A two or three times a day on average, taking about 5 secs to open or close the heavy curtains with the ex-screwdriver motor.

I’m also been toying with the idea of dispensing with batteries and using a mains-derived power supply. But that would mean another largish case alongside the existing compact one. And presumably large heat sinks and consequent nervousness when away.

All ideas would be much appreciated please.

Terry, East Grinstead, UK


Probably simplest for you to increase the charge current. If that's the
route you choose, try ~70mA instead of 35mA. You want to keep the charge
rate to about .05C Note that this is not optimal for the batteries, but
seems the simplest approach.

The N days approach is possible, too, but picking the number N would
be done by trial and error. The problem with charging NiMh is avoiding
overcharge. (In your case, we already know the existing problem is
undercharge.) If during the trial and error the batteries are
overcharged, then the trial and error itself is harming and perhaps
killing them. If you decide to use that approach, I'd try
starting with every other day, charge at 300mA for 1 hour each
charge cycle. Not enough charge? Try every day instead of every
other. Still not enough? increase to 2 hours per day. And so forth.

Regarding using a mains powered supply, you can avoid the large
heat sink issue by using a switching supply instead of a linear
supply. That is likely more costly (around 10 pounds ?) than
other approaches, depending on what you have on hand. But at
least it avoids killing your NiMh's by improper charging.

Ed

Thanks all, very helpful. Just raised the trickle charge to 50 mA for
the present set, rated 2200 mAH. I'll pursue some of the other
suggestions.

Searching didn't find any UK available 'wall warts' or 'AC adapters'
capable of 4A at 5V,and anyway I favour retaining the present design if
possible. It has worked well at times; I've just recalled an earlier
discussion about *reducing* its speed!

A 6V lead acid would need voltage reduction and not confident it could
supply 4A +.

I now have four sets (of three C-Type NiMh), bought over the last few
years, so reluctant to buy yet another fresh set. What diagnostics would
others apply to each set to establish a set's health', apart from trying
it over a period of days?

Directly after charging, the set currently installed was showing 4.3 V
unloaded. In the past that's usually been fine to get the '2.4 V' motor
to do its job, but now needs supplementing with human effort.

Of course, the batteries may not be the cause, or the sole cause,.

Other things under consideration:
- The present motor must be at least 16 years old (I built the project
in 2004), so I could try a new one of identical type I still have.
- Remove the curtains and look for potential 'sticking points'
- Make the regrettable assumption that all four sets are no longer up to
the task and buy a new set of higher quality

For background interest:
https://www.dropbox.com/s/naphd5z44a5m15y/Mechanics.jpg?raw=1



Terry, East Grinstead, UK


if changing batteries you could think about NiCds. Same voltage but more
capable of high load currents (like starting a motor) plus they are more
tolerant of trickle charging.

Thanks, hadn't thought of that. Sort of assumed that Nicads were to
batteries rather like Betamax was to recording media.

I've used BatteriesPlus for NiCds, without problems, e.g.
https://www.batteriesplus.co.uk/acatalog/Sub-C-1300mAh-1-2V-NiCd-Tagged-Battery-1174.html