Maintaining Ni-MH C-types

[david eather]

On 22/02/2020 4:42 am, Terry Pinnell wrote:

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

3 batteries? use 2 7660. My understanding is you cant trickle charge
NiMh at more than the c/100 rate without damage.

 

[Terry Pinnell]

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

On 22/02/2020 4:42 am, Terry Pinnell wrote:
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


3 batteries? use 2 7660. My understanding is you cant trickle charge
NiMh at more than the c/100 rate without damage.

Hopefully not significant damage, but I agree as Ed said up-thread that
it's not 'optimal'. As mentioned, I've increased the trickle charge from
35 mA to 50 mA for the present set and will monitor closely.

I'm pleased to report that's greatly restored the power delivered to the
motor.
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1

Terry, East Grinstead, UK

 

[Rick C]

On Saturday, February 22, 2020 at 4:45:07 AM UTC-5, Terry Pinnell wrote:

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

On 22/02/2020 4:42 am, Terry Pinnell wrote:
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


3 batteries? use 2 7660. My understanding is you cant trickle charge
NiMh at more than the c/100 rate without damage.

Hopefully not significant damage, but I agree as Ed said up-thread that
it's not 'optimal'. As mentioned, I've increased the trickle charge from
35 mA to 50 mA for the present set and will monitor closely.

I'm pleased to report that's greatly restored the power delivered to the
motor.
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1

Terry, East Grinstead, UK

Do you understand that if the battery is not fully charged it's not "trickle" charging? It's just charging.

Why not use a proper charger that measures the voltage and cuts off when near fully charged? That would be the easy solution and can be programmed to keep the battery at any state of charge you desire. It would also allow the use of a smaller set of batteries since it can charge back up much more quickly.

I would also point out that this can be done with a single Li-ion cell at 3..7 to 4.0 volts. If you are using three NiMH cells, this would be a pretty good match. Li-ion tend to have very low impedance as well, meaning it will do a better job of powering the curtain even when partly discharged.

I suspect your NiMH cells are showing their current limitations when partly discharged. NiMH are not as low impedance as NiCd or Li-ion.

Trying to match a varying load with a constant charging current is difficult to say the least. Unless you use a trickle charging tolerant battery chemistry allowing a charging current when fully charged, this is not going to work well. Repeated overcharging of NiMH or NiCd or Li-ion will eventually wear out the cells. If you really insist on trickle charging the battery you need to use a Lead-acid battery or keep the current lower than the allowed level for the NiMH or NiCd cells.

You could provide a better charger that is not strictly a trickle charge. When the battery voltage is lower than terminal, provide more current. That shouldn't be too hard.

--

Rick C.

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

 

[Terry Pinnell]

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

On Saturday, February 22, 2020 at 4:45:07 AM UTC-5, Terry Pinnell wrote:
david eather <eathDELETEer@tpg.com.au> wrote:

On 22/02/2020 4:42 am, Terry Pinnell wrote:
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


3 batteries? use 2 7660. My understanding is you cant trickle charge
NiMh at more than the c/100 rate without damage.

Hopefully not significant damage, but I agree as Ed said up-thread that
it's not 'optimal'. As mentioned, I've increased the trickle charge from
35 mA to 50 mA for the present set and will monitor closely.

I'm pleased to report that's greatly restored the power delivered to the
motor.
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1

Terry, East Grinstead, UK

Do you understand that if the battery is not fully charged it's not "trickle" charging? It's just charging.

Why not use a proper charger that measures the voltage and cuts off when near fully charged? That would be the easy solution and can be programmed to keep the battery at any state of charge you desire. It would also allow the use of a smaller set of batteries since it can charge back up much more quickly.

I would also point out that this can be done with a single Li-ion cell at 3.7 to 4.0 volts. If you are using three NiMH cells, this would be a pretty good match. Li-ion tend to have very low impedance as well, meaning it will do a better job of powering the curtain even when partly discharged.

I suspect your NiMH cells are showing their current limitations when partly discharged. NiMH are not as low impedance as NiCd or Li-ion.

Trying to match a varying load with a constant charging current is difficult to say the least. Unless you use a trickle charging tolerant battery chemistry allowing a charging current when fully charged, this is not going to work well. Repeated overcharging of NiMH or NiCd or Li-ion will eventually wear out the cells. If you really insist on trickle charging the battery you need to use a Lead-acid battery or keep the current lower than the allowed level for the NiMH or NiCd cells.

You could provide a better charger that is not strictly a trickle charge. When the battery voltage is lower than terminal, provide more current. That shouldn't be too hard.

As mentioned in my reply to David yesterday I realise 50 mA is above the
recommended trickle charge rate. And now that performance is apparently
restored, as shown in my video, I'll experiment by nudging the circuit's
current limiting preset back to 30 mA, and see how long it takes to
deteriorate.

I'm also awaiting delivery of the 5V/4A plug-in adapter recommended by
Lasse and will experiment with that too.

Terry, East Grinstead, UK

 

[Rick C]

On Sunday, February 23, 2020 at 10:09:25 AM UTC-5, Terry Pinnell wrote:

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

On Saturday, February 22, 2020 at 4:45:07 AM UTC-5, Terry Pinnell wrote:
david eather <eathDELETEer@tpg.com.au> wrote:

On 22/02/2020 4:42 am, Terry Pinnell wrote:
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


3 batteries? use 2 7660. My understanding is you cant trickle charge
NiMh at more than the c/100 rate without damage.

Hopefully not significant damage, but I agree as Ed said up-thread that
it's not 'optimal'. As mentioned, I've increased the trickle charge from
35 mA to 50 mA for the present set and will monitor closely.

I'm pleased to report that's greatly restored the power delivered to the
motor.
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1

Terry, East Grinstead, UK

Do you understand that if the battery is not fully charged it's not "trickle" charging? It's just charging.

Why not use a proper charger that measures the voltage and cuts off when near fully charged? That would be the easy solution and can be programmed to keep the battery at any state of charge you desire. It would also allow the use of a smaller set of batteries since it can charge back up much more quickly.

I would also point out that this can be done with a single Li-ion cell at 3.7 to 4.0 volts. If you are using three NiMH cells, this would be a pretty good match. Li-ion tend to have very low impedance as well, meaning it will do a better job of powering the curtain even when partly discharged.

I suspect your NiMH cells are showing their current limitations when partly discharged. NiMH are not as low impedance as NiCd or Li-ion.

Trying to match a varying load with a constant charging current is difficult to say the least. Unless you use a trickle charging tolerant battery chemistry allowing a charging current when fully charged, this is not going to work well. Repeated overcharging of NiMH or NiCd or Li-ion will eventually wear out the cells. If you really insist on trickle charging the battery you need to use a Lead-acid battery or keep the current lower than the allowed level for the NiMH or NiCd cells.

You could provide a better charger that is not strictly a trickle charge.. When the battery voltage is lower than terminal, provide more current. That shouldn't be too hard.

As mentioned in my reply to David yesterday I realise 50 mA is above the
recommended trickle charge rate. And now that performance is apparently
restored, as shown in my video, I'll experiment by nudging the circuit's
current limiting preset back to 30 mA, and see how long it takes to
deteriorate.

I'm also awaiting delivery of the 5V/4A plug-in adapter recommended by
Lasse and will experiment with that too.

Terry, East Grinstead, UK

So no consideration of buying or making a proper charger for the batteries you have? Then they would be pretty much always charged up when you need them. By that I mean a charger that would charge them in circuit like your cell phone.

--

Rick C.

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

 

[david eather]

On 24/02/2020 2:31 pm, Rick C wrote:

On Sunday, February 23, 2020 at 10:09:25 AM UTC-5, Terry Pinnell wrote:
Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Saturday, February 22, 2020 at 4:45:07 AM UTC-5, Terry Pinnell wrote:
david eather <eathDELETEer@tpg.com.au> wrote:

On 22/02/2020 4:42 am, Terry Pinnell wrote:
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


3 batteries? use 2 7660. My understanding is you cant trickle charge
NiMh at more than the c/100 rate without damage.

Hopefully not significant damage, but I agree as Ed said up-thread that
it's not 'optimal'. As mentioned, I've increased the trickle charge from
35 mA to 50 mA for the present set and will monitor closely.

I'm pleased to report that's greatly restored the power delivered to the
motor.
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1

Terry, East Grinstead, UK

Do you understand that if the battery is not fully charged it's not "trickle" charging? It's just charging.

Why not use a proper charger that measures the voltage and cuts off when near fully charged? That would be the easy solution and can be programmed to keep the battery at any state of charge you desire. It would also allow the use of a smaller set of batteries since it can charge back up much more quickly.

I would also point out that this can be done with a single Li-ion cell at 3.7 to 4.0 volts. If you are using three NiMH cells, this would be a pretty good match. Li-ion tend to have very low impedance as well, meaning it will do a better job of powering the curtain even when partly discharged.

I suspect your NiMH cells are showing their current limitations when partly discharged. NiMH are not as low impedance as NiCd or Li-ion.

Trying to match a varying load with a constant charging current is difficult to say the least. Unless you use a trickle charging tolerant battery chemistry allowing a charging current when fully charged, this is not going to work well. Repeated overcharging of NiMH or NiCd or Li-ion will eventually wear out the cells. If you really insist on trickle charging the battery you need to use a Lead-acid battery or keep the current lower than the allowed level for the NiMH or NiCd cells.

You could provide a better charger that is not strictly a trickle charge. When the battery voltage is lower than terminal, provide more current. That shouldn't be too hard.

As mentioned in my reply to David yesterday I realise 50 mA is above the
recommended trickle charge rate. And now that performance is apparently
restored, as shown in my video, I'll experiment by nudging the circuit's
current limiting preset back to 30 mA, and see how long it takes to
deteriorate.

I'm also awaiting delivery of the 5V/4A plug-in adapter recommended by
Lasse and will experiment with that too.

Terry, East Grinstead, UK

So no consideration of buying or making a proper charger for the batteries you have? Then they would be pretty much always charged up when you need them. By that I mean a charger that would charge them in circuit like your cell phone.

the batteries he has are probably already stuffed

 

[Clive Arthur]

On 21/02/2020 18:29, Terry Pinnell wrote:
> david eather <eathDELETEer@tpg.com.au> wrote:

<snipped>

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

Supercaps? Very long life, charge with ickle trickle or fast if you want.

4A at 4.8V for 5s is 90J which is about 8F at 4.8V, but of course the
voltage droops on discharge, but I see eBay has eg 2.7V 500F caps, use
two in series?

--
Cheers
Clive

 

On Monday, 24 February 2020 09:54:33 UTC, Clive Arthur wrote:

> Supercaps? Very long life, charge with ickle trickle or fast if you want.

and replace your curtain motor with a whacking great solenoid Fastest curtain opener in the west!


NT

 

[Clive Arthur]

On 25/02/2020 02:06, tabbypurr@gmail.com wrote:

On Monday, 24 February 2020 09:54:33 UTC, Clive Arthur wrote:

Supercaps? Very long life, charge with ickle trickle or fast if you want.

and replace your curtain motor with a whacking great solenoid Fastest curtain opener in the west!


NT

You could use it as a shutter in a Camera Obscura

--
Cheers
Clive

 

[Clive Arthur]

On 25/02/2020 11:04, Terry Pinnell wrote:

Clive Arthur <cliveta@nowaytoday.co.uk> wrote:

On 21/02/2020 18:29, Terry Pinnell wrote:
david eather <eathDELETEer@tpg.com.au> wrote:

snipped

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

Supercaps? Very long life, charge with ickle trickle or fast if you want.

4A at 4.8V for 5s is 90J which is about 8F at 4.8V, but of course the
voltage droops on discharge, but I see eBay has eg 2.7V 500F caps, use
two in series?


Thanks Clive, I may well order a couple out of curiosity as I've never
used a supercapacitor before. And for a short burst as in this
application they would seem ideal. However the three hits I followed up
on ebay.co.uk all appeared to be from the same source. In the current
situation I wonder if even 11th May is likely?

"Get it by Tue, 24 Mar - Mon, 11 May from Shenzhen, China"

--------------------

Could you explain your calculation of 90J please? I see its formula is:
0.5 * C * V^2 which would give about 0.5 * 500 * 22 = 5500J not 90J ?

Terry, East Grinstead, UK

The 90J is 4A at 4.8V (ie 19.2W) for 5s. You'd need a few times more
than that without using complicated circuitry, as the capacitor voltage
would drop as it discharged.

You're right with the 5.5kJ, much more than you need, but that won't
matter and they're (probably) available, though also probably the
capacitance is exaggerated. By all means use less, but if you wanted to
close then immediately open, that's 10 seconds at 19.2W etc...

And be careful of corona discharge with these Chinese caps ;-) [FAOD
that was a joke.]

--
Cheers
Clive

 

[Terry Pinnell]

tabbypurr@gmail.com wrote:

On Monday, 24 February 2020 09:54:33 UTC, Clive Arthur wrote:

Supercaps? Very long life, charge with ickle trickle or fast if you want.

and replace your curtain motor with a whacking great solenoid Fastest curtain opener in the west!


NT

With some massive gearing and a section of bungee cord to cushion the
impact?

Terry, East Grinstead, UK

 

[Terry Pinnell]

Clive Arthur <cliveta@nowaytoday.co.uk> wrote:

On 21/02/2020 18:29, Terry Pinnell wrote:
david eather <eathDELETEer@tpg.com.au> wrote:

snipped

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

Supercaps? Very long life, charge with ickle trickle or fast if you want.

4A at 4.8V for 5s is 90J which is about 8F at 4.8V, but of course the
voltage droops on discharge, but I see eBay has eg 2.7V 500F caps, use
two in series?

Thanks Clive, I may well order a couple out of curiosity as I've never
used a supercapacitor before. And for a short burst as in this
application they would seem ideal. However the three hits I followed up
on ebay.co.uk all appeared to be from the same source. In the current
situation I wonder if even 11th May is likely?

"Get it by Tue, 24 Mar - Mon, 11 May from Shenzhen, China"

--------------------

Could you explain your calculation of 90J please? I see its formula is:
0.5 * C * V^2 which would give about 0.5 * 500 * 22 = 5500J not 90J ?

Terry, East Grinstead, UK

 

[Terry Pinnell]

Terry Pinnell <me@somewhere.invalid> wrote:

Clive Arthur <cliveta@nowaytoday.co.uk> wrote:

On 21/02/2020 18:29, Terry Pinnell wrote:
david eather <eathDELETEer@tpg.com.au> wrote:

snipped

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

Supercaps? Very long life, charge with ickle trickle or fast if you want.

4A at 4.8V for 5s is 90J which is about 8F at 4.8V, but of course the
voltage droops on discharge, but I see eBay has eg 2.7V 500F caps, use
two in series?


Thanks Clive, I may well order a couple out of curiosity as I've never
used a supercapacitor before. And for a short burst as in this
application they would seem ideal. However the three hits I followed up
on ebay.co.uk all appeared to be from the same source. In the current
situation I wonder if even 11th May is likely?

"Get it by Tue, 24 Mar - Mon, 11 May from Shenzhen, China"

--------------------

Could you explain your calculation of 90J please? I see its formula is:
0.5 * C * V^2 which would give about 0.5 * 500 * 22 = 5500J not 90J ?

Terry, East Grinstead, UK

Anyway, at that price it's no big deal so I've ordered three. It will be
interesting to see when they arrive ;-)

Terry, East Grinstead, UK

 

[Rick C]

On Tuesday, February 25, 2020 at 6:23:59 AM UTC-5, Clive Arthur wrote:

On 25/02/2020 11:04, Terry Pinnell wrote:
Clive Arthur <cliveta@nowaytoday.co.uk> wrote:

On 21/02/2020 18:29, Terry Pinnell wrote:
david eather <eathDELETEer@tpg.com.au> wrote:

snipped

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

Supercaps? Very long life, charge with ickle trickle or fast if you want.

4A at 4.8V for 5s is 90J which is about 8F at 4.8V, but of course the
voltage droops on discharge, but I see eBay has eg 2.7V 500F caps, use
two in series?


Thanks Clive, I may well order a couple out of curiosity as I've never
used a supercapacitor before. And for a short burst as in this
application they would seem ideal. However the three hits I followed up
on ebay.co.uk all appeared to be from the same source. In the current
situation I wonder if even 11th May is likely?

"Get it by Tue, 24 Mar - Mon, 11 May from Shenzhen, China"

--------------------

Could you explain your calculation of 90J please? I see its formula is:
0.5 * C * V^2 which would give about 0.5 * 500 * 22 = 5500J not 90J ?

Terry, East Grinstead, UK

The 90J is 4A at 4.8V (ie 19.2W) for 5s. You'd need a few times more
than that without using complicated circuitry, as the capacitor voltage
would drop as it discharged.

You're right with the 5.5kJ, much more than you need, but that won't
matter and they're (probably) available, though also probably the
capacitance is exaggerated. By all means use less, but if you wanted to
close then immediately open, that's 10 seconds at 19.2W etc...

And be careful of corona discharge with these Chinese caps ;-) [FAOD
that was a joke.]

Not a very good one.

--

Rick C.

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

 

[ehsjr]

On 2/22/2020 4:45 AM, Terry Pinnell wrote:

<snip>

I'm pleased to report that's greatly restored the power delivered to the
motor.
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1

Now THAT's a good movie!
Ed

Terry, East Grinstead, UK

 

[Terry Pinnell]

Terry Pinnell <me@somewhere.invalid> wrote:

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

Unfortunately that 4A 5V supply adapter
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
strangely does not work with this motor.

I'll include details in a fresh post.

Terry, East Grinstead, UK