Device to open a circuit when a voltage is released?

[Bruce W.1]

Does anyone know of a pre-made device or simple circuit that opens a set
of contacts when a certain voltage is met? I want to use it mostly to
charge and discharge batteries.

Building this would probably be easy, except the tricky part would be
the ability to change the trigger voltage. This would need to be
programmable, or I could settle with presets for every voltage between 1
and 15 in half volt increments.

Does anyone know of such a device?

Thanks for your help.

 

[Active8]

On Fri, 18 Mar 2005 02:15:25 GMT, Bruce W.1 wrote:

Does anyone know of a pre-made device or simple circuit that opens a set
of contacts when a certain voltage is met? I want to use it mostly to
charge and discharge batteries.

Building this would probably be easy, except the tricky part would be
the ability to change the trigger voltage. This would need to be
programmable, or I could settle with presets for every voltage between 1
and 15 in half volt increments.

Does anyone know of such a device?

It's called a battery charger. There's a few NiCd/NiMH charger
circuits you can find via google. You can also learn about charging
rates that way. You'll find some stuff in the R/C modeler's sites -
even articles on discharging. I forget some of it, but if you're
under the impression that you have to discharge batteries often to
prevent mythical memory effects, you'll shorten their life.

There's some info here, but I doubt you want to deal with the PIC.

http://www.angelfire.com/electronic/hayles/charge1.html

A FAQ:

http://www.repairfaq.org/ELE/F_Battery_info.html

This one wasn't as easy as I thought to find on the net, but it
might help:

http://www.solorb.com/elect/tmpchrg/

It has a temperature monitor. The thing I like is that it works like
the charger for cordless drill batts which have built in thermistors
to signal the charger that it's time to quit. Contrast that with an
auto batt charger which supplies a voltage and you know it's charged
when the charging current goes to zero or close to it.

If you need help modifying a circuit to meet your needs, we can
help.

I think the enclosure for one of these projects will make it more
expensive than an off the shelf solution, but I don't know your
motivtion for wanting to build.
--
Best Regards,
Mike

 

[Bruce W.1]

Active8 wrote:

It's called a battery charger. There's a few NiCd/NiMH charger
circuits you can find via google. You can also learn about charging
rates that way. You'll find some stuff in the R/C modeler's sites -
even articles on discharging. I forget some of it, but if you're
under the impression that you have to discharge batteries often to
prevent mythical memory effects, you'll shorten their life.

There's some info here, but I doubt you want to deal with the PIC.

http://www.angelfire.com/electronic/hayles/charge1.html

A FAQ:

http://www.repairfaq.org/ELE/F_Battery_info.html

This one wasn't as easy as I thought to find on the net, but it
might help:

http://www.solorb.com/elect/tmpchrg/

It has a temperature monitor. The thing I like is that it works like
the charger for cordless drill batts which have built in thermistors
to signal the charger that it's time to quit. Contrast that with an
auto batt charger which supplies a voltage and you know it's charged
when the charging current goes to zero or close to it.

If you need help modifying a circuit to meet your needs, we can
help.

I think the enclosure for one of these projects will make it more
expensive than an off the shelf solution, but I don't know your
motivtion for wanting to build.
=================================================

I own a number of battery chargers as well as voltage logging software.
Unfortunately the software does not have an alarm or alert.

All chargers/dischargers have shortcomings, like the ability to change
parameters like the rate of charge/discharge, discharge depth, etc.. So
sometimes I do it manually.

When doing it manually sometimes I forget to watch it. That's why I'm
seeking a device to either set off an alarm or kill the process when a
certain voltage is met.

If I can't find one manufactured then I'll have to build it instead.

 

[Active8]

On Fri, 18 Mar 2005 16:13:55 GMT, Bruce W.1 wrote:

Active8 wrote:
It's called a battery charger. There's a few NiCd/NiMH charger
circuits you can find via google. You can also learn about charging
rates that way. You'll find some stuff in the R/C modeler's sites -
even articles on discharging. I forget some of it, but if you're
under the impression that you have to discharge batteries often to
prevent mythical memory effects, you'll shorten their life.

There's some info here, but I doubt you want to deal with the PIC.

http://www.angelfire.com/electronic/hayles/charge1.html

A FAQ:

http://www.repairfaq.org/ELE/F_Battery_info.html

This one wasn't as easy as I thought to find on the net, but it
might help:

http://www.solorb.com/elect/tmpchrg/

It has a temperature monitor. The thing I like is that it works like
the charger for cordless drill batts which have built in thermistors
to signal the charger that it's time to quit. Contrast that with an
auto batt charger which supplies a voltage and you know it's charged
when the charging current goes to zero or close to it.

If you need help modifying a circuit to meet your needs, we can
help.

I think the enclosure for one of these projects will make it more
expensive than an off the shelf solution, but I don't know your
motivtion for wanting to build.
=================================================

I own a number of battery chargers as well as voltage logging software.
Unfortunately the software does not have an alarm or alert.

All chargers/dischargers have shortcomings, like the ability to change
parameters like the rate of charge/discharge, discharge depth, etc.. So
sometimes I do it manually.

When doing it manually sometimes I forget to watch it. That's why I'm
seeking a device to either set off an alarm or kill the process when a
certain voltage is met.

If I can't find one manufactured then I'll have to build it instead.

I doubt you find an off the shelf unit. If you'd have read the links
I gave you, you'd have found the Max712/Max713 fast/trickle charge
chips. Anything wrong with those? 1 - 16 cells. No discharge feature
mentioned, but that could be a separate circuit.

The temperature controlled charger or at least that part of the
circuit, is a good idea. It'll shut off if your charging rate causes
overheating. For fast charging a comparator with voltage reference
would do the job.

You said programmable from 1 - 15 in .5 volt steps. What kind of
programming? PIC based? You could use an LM317 regulator and pot for
the reference and meter the trip point. Or use a PIC with ADC. PICs
also come with comparitors, so there's lots of options here.
--
Best Regards,
Mike

 

[Rich Grise]

On Fri, 18 Mar 2005 16:13:55 +0000, Bruce W.1 wrote:

I own a number of battery chargers as well as voltage logging software.
Unfortunately the software does not have an alarm or alert.

All chargers/dischargers have shortcomings, like the ability to change
parameters like the rate of charge/discharge, discharge depth, etc.. So
sometimes I do it manually.

When doing it manually sometimes I forget to watch it. That's why I'm
seeking a device to either set off an alarm or kill the process when a
certain voltage is met.

If I can't find one manufactured then I'll have to build it instead.

Well, there's always these:
http://www.alarmclocksonline.com/10607.htm
;-)

But seriously - what is the software, and what's it running on? It seems
that'd be the most elegant way to do this - just fix the software, so it
can give an indication of some kind, or if it's in a control loop it
could do the switching.

Failing that, just a comparator and sonalert will do what you want.
http://www.google.com/search?hl=en&ie=ISO-8859-1&q=comparator+circuit&btnG=Google+Search

I'm too lazy to draw an ASCII circuit, but basically it's a voltage
divider to one input, a settable reference to the other, a little positive
feedback for hysteresis, and a beeper.

Good Luck!
Rich

 

[Active8]

On Fri, 18 Mar 2005 18:51:00 GMT, Rich Grise wrote:

On Fri, 18 Mar 2005 16:13:55 +0000, Bruce W.1 wrote:

I own a number of battery chargers as well as voltage logging software.
Unfortunately the software does not have an alarm or alert.

All chargers/dischargers have shortcomings, like the ability to change
parameters like the rate of charge/discharge, discharge depth, etc.. So
sometimes I do it manually.

When doing it manually sometimes I forget to watch it. That's why I'm
seeking a device to either set off an alarm or kill the process when a
certain voltage is met.

If I can't find one manufactured then I'll have to build it instead.

Well, there's always these:
http://www.alarmclocksonline.com/10607.htm
;-)

Nice Big Ben.

But seriously - what is the software, and what's it running on? It seems
that'd be the most elegant way to do this - just fix the software, so it
can give an indication of some kind, or if it's in a control loop it
could do the switching.

Failing that, just a comparator and sonalert will do what you want.
http://www.google.com/search?hl=en&ie=ISO-8859-1&q=comparator+circuit&btnG=Google+Search

Yeah, but his exisiting chargers are lacking features.
--
Best Regards,
Mike

 

[mike]

Bruce W.1 wrote:

mike wrote:

All you need is a comparator and a relay.
Only you know your application.

BUT.
Think about better than half volt resolution.
Half a volt at 1V is BIG.
Even on a 10-cell pack, half a volt can mean the difference between OK
and smoked battery. Then you need to figure out the value to set.

FWIW, I've been plotting charge curves on various kinds of batteries.
Depending on age, history, size, type, the peak voltage of the charge
curve varies all over the map. The only cells I've had terminate
charge on overvoltage were those seriously worn out.

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

===================================================

A voltage comparator and a relay. I like that idea. Off the same
regulated power supply that's running the charge or discharge circuit I
could make a voltage divider with a rheostat.

But what if the voltage is going up (charge) or down (discharge)? Guess
I should read-up on voltage comparators.

swap the comparator inputs with a up/down switch.
mike

--
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with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
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[Active8]

On Fri, 18 Mar 2005 14:58:25 -0800, mike wrote:

Bruce W.1 wrote:
snip

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

Slope termination... You mean throttle back the charging rate
(current)?
--
Best Regards,
Mike

 

[Active8]

On Sat, 19 Mar 2005 00:43:19 GMT, Bruce W.1 wrote:

mike wrote:

All you need is a comparator and a relay.
Only you know your application.

BUT.
Think about better than half volt resolution.
Half a volt at 1V is BIG.
Even on a 10-cell pack, half a volt can mean the difference between OK
and smoked battery. Then you need to figure out the value to set.

FWIW, I've been plotting charge curves on various kinds of batteries.
Depending on age, history, size, type, the peak voltage of the charge
curve varies all over the map. The only cells I've had terminate charge
on overvoltage were those seriously worn out.

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

===================================================

A voltage comparator and a relay. I like that idea. Off the same
regulated power supply that's running the charge or discharge circuit I
could make a voltage divider with a rheostat.

But what if the voltage is going up (charge) or down (discharge)? Guess
I should read-up on voltage comparators.

When you're done, re-read my posts and see that that's one of the
solutions I mentioned, but I suggested a regulator to set the trip
point - might not need that. I figured you knew what a comparator
was and that you knew you could control a relay with it.
--
Best Regards,
Mike

 

[mike]

Active8 wrote:

On Fri, 18 Mar 2005 14:58:25 -0800, mike wrote:


Bruce W.1 wrote:

snip

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike


Slope termination... You mean throttle back the charging rate
(current)?

I don't understand what you mean.

What I meant was...
Depending on the cell chemistry, terminate when dV/dt is appropriate
with safety termination on temperature limit.
mike

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[Active8]

On Sat, 19 Mar 2005 08:34:05 -0800, mike wrote:

Active8 wrote:
On Fri, 18 Mar 2005 14:58:25 -0800, mike wrote:

Bruce W.1 wrote:

snip

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

Slope termination... You mean throttle back the charging rate
(current)?

I don't understand what you mean.

I meant that I didn't understand what you meant

What I meant was...
Depending on the cell chemistry, terminate when dV/dt is appropriate
with safety termination on temperature limit.

Oh! *That* slope.

I'd think that when a cell of any chemistry is almost done charging,
that a continued constant current charge would stress it and isn't
that why it heats up? IIRC the internal resistance of the cell drops
as it's voltage increases. I think that is what leads to the temp
rise.
--
Best Regards,
Mike

 

[mike]

Active8 wrote:

On Sat, 19 Mar 2005 08:34:05 -0800, mike wrote:


Active8 wrote:

On Fri, 18 Mar 2005 14:58:25 -0800, mike wrote:


Bruce W.1 wrote:

snip

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

Slope termination... You mean throttle back the charging rate
(current)?

I don't understand what you mean.


I meant that I didn't understand what you meant

What I meant was...
Depending on the cell chemistry, terminate when dV/dt is appropriate
with safety termination on temperature limit.


Oh! *That* slope.

I'd think that when a cell of any chemistry is almost done charging,
that a continued constant current charge would stress it and isn't
that why it heats up? IIRC the internal resistance of the cell drops
as it's voltage increases. I think that is what leads to the temp
rise.

Suggest you do some more research.
In my experience, a properly charged cell with dV/dt termination does
NOT heat much. The only reason for the temperature cutoff is SAFETY
when something goes wrong. With -dV/dt cutoff, the most likely
combination of factors is 1) low charge current, 2)mismatched initial
state of charge so they peak at different times and the total curve of
the sum of the series string never goes negative. THEN it gets hot.

Another problem situation is with a poorly designed charger that depends
on none of the cells being shorted.
mike

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[Active8]

On Sat, 19 Mar 2005 17:30:06 -0800, mike wrote:

Active8 wrote:
On Sat, 19 Mar 2005 08:34:05 -0800, mike wrote:

Active8 wrote:

On Fri, 18 Mar 2005 14:58:25 -0800, mike wrote:


Bruce W.1 wrote:

snip

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

Slope termination... You mean throttle back the charging rate
(current)?

I don't understand what you mean.

I meant that I didn't understand what you meant

What I meant was...
Depending on the cell chemistry, terminate when dV/dt is appropriate
with safety termination on temperature limit.

Oh! *That* slope.

I'd think that when a cell of any chemistry is almost done charging,
that a continued constant current charge would stress it and isn't
that why it heats up? IIRC the internal resistance of the cell drops
as it's voltage increases. I think that is what leads to the temp
rise.

Suggest you do some more research.

I said "I'd think...".

I plan to whenever I get around to that deep cycle charger I'll
need. No need to worry about NiCds now.

I'm going to put each separate thought in it's own paragraph so you
don't misunderstand me. Read them as if the others weren't there.

In my experience, a properly charged cell with dV/dt termination does
NOT heat much.

Nothing I said was intended to suggest that it would. I opined that
a constant current all the way up to the end might heat it up.

I said that IIRC the internal resistance of a cell decreases as it
reached full charge.

I said I think that a current through a small valued resistor causes
more heat (heat = work = energy = P*T) than the same current through
a larger value resistor.

I don't have any charge curves handy AFAIK but I'm guessing (hell, I
can almost picture curves I've seen in the past) that when it's
almost up to full charge, dV/dt is less than when it started
charging.

I take it you mean it's always under constant current charge for the
dV/dt in question.

The only reason for the temperature cutoff is SAFETY
when something goes wrong.

My cordless drill batts have a thermistor inside. I thought that was
the *only* thing that stops the charge.

With -dV/dt cutoff, the most likely

Now I have a minus sign to ponder.

combination of factors is 1) low charge current, 2)mismatched initial
state of charge so they peak at different times and the total curve of
the sum of the series string never goes negative.

Is that the -dV/dt above? The cell or string starts uncharging?

THEN it gets hot.

Another problem situation is with a poorly designed charger that depends
on none of the cells being shorted.

I'd like to know how to detect and/or deal with that situation. I'd
guess that I'd have to determine that the string never reached it's
expected voltage at the expected time.
--
Best Regards,
Mike

 

[mike]

Active8 wrote:

On Sat, 19 Mar 2005 17:30:06 -0800, mike wrote:


Active8 wrote:

On Sat, 19 Mar 2005 08:34:05 -0800, mike wrote:


Active8 wrote:


On Fri, 18 Mar 2005 14:58:25 -0800, mike wrote:



Bruce W.1 wrote:

snip

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

Slope termination... You mean throttle back the charging rate
(current)?

I don't understand what you mean.

I meant that I didn't understand what you meant


What I meant was...
Depending on the cell chemistry, terminate when dV/dt is appropriate
with safety termination on temperature limit.

Oh! *That* slope.

I'd think that when a cell of any chemistry is almost done charging,
that a continued constant current charge would stress it and isn't
that why it heats up? IIRC the internal resistance of the cell drops
as it's voltage increases. I think that is what leads to the temp
rise.

Suggest you do some more research.


I said "I'd think...".

I plan to whenever I get around to that deep cycle charger I'll
need. No need to worry about NiCds now.

I'm going to put each separate thought in it's own paragraph so you
don't misunderstand me. Read them as if the others weren't there.

Thanks, I need all the help I can get.

In my experience, a properly charged cell with dV/dt termination does
NOT heat much.


Nothing I said was intended to suggest that it would. I opined that
a constant current all the way up to the end might heat it up.

I said that IIRC the internal resistance of a cell decreases as it
reached full charge.

I said I think that a current through a small valued resistor causes
more heat (heat = work = energy = P*T) than the same current through
a larger value resistor.

Mr. Ohm and those starting from his equations are all turning over in
their graves about now.

I don't have any charge curves handy AFAIK but I'm guessing (hell, I
can almost picture curves I've seen in the past) that when it's
almost up to full charge, dV/dt is less than when it started
charging.

I'm not guessing, my battery charger plots the curves every time it charges.
For NiCds dV/dt peaks before it levels off then turns negative.

I take it you mean it's always under constant current charge for the
dV/dt in question.

That's a reasonable assumption.

The only reason for the temperature cutoff is SAFETY
when something goes wrong.


My cordless drill batts have a thermistor inside. I thought that was
the *only* thing that stops the charge.

It is. There are many cheap chargers that do just that. They charge
the thing until it gets hot enough to turn off. Great way to cook
batteries to death. I've rebuilt about a dozen drill packs. Usually,
all the cells have vented.
FWIW, this technique works reasonably if you
fully discharge the pack...but not too fully to reverse a cell...before
charging. During the full recharge time, there's enough heat built up
to bring the thermal mass up to cutoff without serious damage. Problem
is when you put a 70% charged pack on charge. The internal temperature
comes up too fast for the external sensor to trip. Cell vents.

A key phrase seems to have been snipped from my earlier post"
"In my experience, a properly charged cell..."
Temperature only cutoff is not a properly designed charger.
Today, you'd use that only if you cared about the lowest possible
product sales price, and you made a bundle off replacement batteries.

With -dV/dt cutoff, the most likely


Now I have a minus sign to ponder.

Google 0-delta-v or -delta-v or some permutation of spaces and dashes.

combination of factors is 1) low charge current, 2)mismatched initial
state of charge so they peak at different times and the total curve of
the sum of the series string never goes negative.


Is that the -dV/dt above? The cell or string starts uncharging?

Nope, still charging. There's lots of stuff on the web on proper
charging of NiCd cells.
Google 0-delta-v or -delta-v or some permutation of spaces and dashes.
Or start at the cadex website.

THEN it gets hot.

Another problem situation is with a poorly designed charger that depends
on none of the cells being shorted.


I'd like to know how to detect and/or deal with that situation. I'd
guess that I'd have to determine that the string never reached it's
expected voltage at the expected time.

No problem. Make the charge current independent of pack voltage.
Charge at the proper current relative to cell capacity. (there's
argument over exactly what this is. I usually use C"
Terminate on voltage slope rather than voltage.
Have three safety cutoffs
1)over temperature
2)over voltage
3)over charge I x T > 1.2 x pack capacity
And apply a trickle charge if the pack voltage is below some minimum
voltage. Only start fast charge if the pack voltage is within some
min/max range and the temperature is within some min/max range.

The only reason my charger needs to know the voltage is so it can
properly normalize the graph so every pack looks the same on screen
and I can immediately recognize a problem.

mike
--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[Active8]

On Sun, 20 Mar 2005 04:55:43 -0800, mike wrote:

Active8 wrote:
snip

I'm going to put each separate thought in it's own paragraph so you
don't misunderstand me. Read them as if the others weren't there.

Thanks, I need all the help I can get.

I respect your modesty. Commo's a bitch sometimes.

In my experience, a properly charged cell with dV/dt termination does
NOT heat much.

Nothing I said was intended to suggest that it would. I opined that
a constant current all the way up to the end might heat it up.

I said that IIRC the internal resistance of a cell decreases as it
reached full charge.

I said I think that a current through a small valued resistor causes
more heat (heat = work = energy = P*T) than the same current through
a larger value resistor.

Mr. Ohm and those starting from his equations are all turning over in
their graves about now.

And yet again my heads up my ass[-]backwards! Caffeine, sugar and
a long day or two? Day/night - whatever it was. "A V across..." That
kills that hypothesis.

I don't have any charge curves handy AFAIK but I'm guessing (hell, I
can almost picture curves I've seen in the past) that when it's
almost up to full charge, dV/dt is less than when it started
charging.

I'm not guessing, my battery charger plots the curves every time it charges.
For NiCds dV/dt peaks before it levels off then turns negative.

Got some returns on dV/dt and dT/dt. It sounds similar to a slight
peak at the cutoff of a LP filter. From the recombination. I
probably saw that in the curves from the enerhell (sic) quidbook,
wherever that is at the moment. Last I checked, the online thing
sucked.

"With the NiMH battery the voltage depression is smaller, and harder
to detect than with the NiCad battery"

I take it you mean it's always under constant current charge for the
dV/dt in question.

That's a reasonable assumption.


The only reason for the temperature cutoff is SAFETY
when something goes wrong.

My cordless drill batts have a thermistor inside. I thought that was
the *only* thing that stops the charge.

It is. There are many cheap chargers that do just that. They charge
the thing until it gets hot enough to turn off. Great way to cook
batteries to death. I've rebuilt about a dozen drill packs. Usually,
all the cells have vented.
FWIW, this technique works reasonably if you
fully discharge the pack...but not too fully to reverse a cell...before
charging. During the full recharge time, there's enough heat built up
to bring the thermal mass up to cutoff without serious damage. Problem
is when you put a 70% charged pack on charge. The internal temperature
comes up too fast for the external sensor to trip. Cell vents.

A key phrase seems to have been snipped from my earlier post"
"In my experience, a properly charged cell..."

"with dV/dt termination does
NOT heat much."

It's up there below my first comment. We'd have lost nothing if it
were snipped, I got it the first time. Didn't mean to suggest
otherwise.

Temperature only cutoff is not a properly designed charger.
Today, you'd use that only if you cared about the lowest possible
product sales price, and you made a bundle off replacement batteries.


With -dV/dt cutoff, the most likely

Now I have a minus sign to ponder.

Google 0-delta-v or -delta-v or some permutation of spaces and dashes.


combination of factors is 1) low charge current, 2)mismatched initial
state of charge so they peak at different times and the total curve of
the sum of the series string never goes negative.

Is that the -dV/dt above? The cell or string starts uncharging?

Nope, still charging. There's lots of stuff on the web on proper
charging of NiCd cells.

I read only a bit of what I've stumbled across years ago re: R/C.

Google 0-delta-v or -delta-v or some permutation of spaces and dashes.
Or start at the cadex website.

THEN it gets hot.

Another problem situation is with a poorly designed charger that depends
on none of the cells being shorted.

I'd like to know how to detect and/or deal with that situation. I'd
guess that I'd have to determine that the string never reached it's
expected voltage at the expected time.

No problem. Make the charge current independent of pack voltage.
Charge at the proper current relative to cell capacity. (there's
argument over exactly what this is. I usually use C"

The quote is not a typo?

Terminate on voltage slope rather than voltage.
Have three safety cutoffs
1)over temperature
2)over voltage
3)over charge I x T > 1.2 x pack capacity
And apply a trickle charge if the pack voltage is below some minimum
voltage. Only start fast charge if the pack voltage is within some
min/max range and the temperature is within some min/max range.

The only reason my charger needs to know the voltage is so it can
properly normalize the graph so every pack looks the same on screen
and I can immediately recognize a problem.

If the day comes that I need to really get into it, I can add that

logging into one of my progs. How many uses for a DSP/FIR/IIR with
time domain/freq domain and plotting prog?

What is this? :

http://www.repairfaq.org/ELE/F_Battery_info.html

seach find: "Type ANSI" (no quotes)

What's this C5maH ? 5*C in maH ?

Hey! I think we did well on commo this time. And with me wired on
caffeine.
--
Best Regards,
Mike

 

[mike]

Active8 wrote:
snip

What is this? :

http://www.repairfaq.org/ELE/F_Battery_info.html

seach find: "Type ANSI" (no quotes)

What's this C5maH ? 5*C in maH ?

It's right under the chart:
Note that this is the capacity when the battery is discharged over 5
hours time period.

Remember that cell capacities are 3-4X what they were when that was written.
mike

Hey! I think we did well on commo this time. And with me wired on
caffeine.

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[mike]

Bruce W.1 wrote:

Does anyone know of a pre-made device or simple circuit that opens a set
of contacts when a certain voltage is met? I want to use it mostly to
charge and discharge batteries.

Building this would probably be easy, except the tricky part would be
the ability to change the trigger voltage. This would need to be
programmable, or I could settle with presets for every voltage between 1
and 15 in half volt increments.

Does anyone know of such a device?

Thanks for your help.

All you need is a comparator and a relay.
Only you know your application.

BUT.
Think about better than half volt resolution.
Half a volt at 1V is BIG.
Even on a 10-cell pack, half a volt can mean the difference between OK
and smoked battery. Then you need to figure out the value to set.

FWIW, I've been plotting charge curves on various kinds of batteries.
Depending on age, history, size, type, the peak voltage of the charge
curve varies all over the map. The only cells I've had terminate charge
on overvoltage were those seriously worn out.

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

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with links. Delete this sig when replying.
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Wanted, PCMCIA SCSI Card for HP m820 CDRW.
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Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
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[Bruce W.1]

mike wrote:

All you need is a comparator and a relay.
Only you know your application.

BUT.
Think about better than half volt resolution.
Half a volt at 1V is BIG.
Even on a 10-cell pack, half a volt can mean the difference between OK
and smoked battery. Then you need to figure out the value to set.

FWIW, I've been plotting charge curves on various kinds of batteries.
Depending on age, history, size, type, the peak voltage of the charge
curve varies all over the map. The only cells I've had terminate charge
on overvoltage were those seriously worn out.

It's much safer and less stressful on the cells if you use some kind of
slope termination with a secondary safety based on temperature.
mike

===================================================

A voltage comparator and a relay. I like that idea. Off the same
regulated power supply that's running the charge or discharge circuit I
could make a voltage divider with a rheostat.

But what if the voltage is going up (charge) or down (discharge)? Guess
I should read-up on voltage comparators.

 

[Active8]

On Sun, 20 Mar 2005 17:49:45 -0800, mike wrote:

Active8 wrote:
snip

What is this? :

http://www.repairfaq.org/ELE/F_Battery_info.html

seach find: "Type ANSI" (no quotes)

What's this C5maH ? 5*C in maH ?

It's right under the chart:
Note that this is the capacity when the battery is discharged over 5
hours time period.

Oh. I read the lines below, duh. At any discharge rate? Is it a
permanent loss of capacity?

Remember that cell capacities are 3-4X what they were when that was written.

About that dV/dt thing:

"Another reason memory effect is a myth since all the consumer
charger's I've seen actually overcharge until there is a slight
voltage drop (due to an increase in resistance from the formation of
larger cadmium hydroxide particules that cause contact loss). It's
because consumer chargers actually overcharge that you have to give
the battery a deep discharge from time to time. It has nothing to do
with memory."

Does this mean that they go further into voltage depression than you
would allow them using the technique you recommend?
--
Best Regards,
Mike