| Author |
Message |
Bruce W.1
Guest
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 Posted:
Fri Mar 18, 2005 6:10 am Post subject:
Device to open a circuit when a voltage is released? |
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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.
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Active8
Guest
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| Posted:
Fri Mar 18, 2005 12:43 pm Post subject:
Re: Device to open a circuit when a voltage is released? |
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On Fri, 18 Mar 2005 02:15:25 GMT, Bruce W.1 wrote:
| Quote: | 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 |
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Bruce W.1
Guest
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| Posted:
Fri Mar 18, 2005 10:13 pm Post subject:
Re: Device to open a circuit when a voltage is released? |
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Active8 wrote:
| Quote: | 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.
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Active8
Guest
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| Posted:
Sat Mar 19, 2005 12:45 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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On Fri, 18 Mar 2005 16:13:55 GMT, Bruce W.1 wrote:
| Quote: | 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 |
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Rich Grise
Guest
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| Posted:
Sat Mar 19, 2005 12:51 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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On Fri, 18 Mar 2005 16:13:55 +0000, Bruce W.1 wrote:
| Quote: | 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 |
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Active8
Guest
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| Posted:
Sat Mar 19, 2005 1:56 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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On Fri, 18 Mar 2005 18:51:00 GMT, Rich Grise wrote:
| Quote: | 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.
Yeah, but his exisiting chargers are lacking features.
--
Best Regards,
Mike |
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mike
Guest
|
| Posted:
Sat Mar 19, 2005 4:58 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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Bruce W.1 wrote:
| Quote: | 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
--
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/ |
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Bruce W.1
Guest
|
| Posted:
Sat Mar 19, 2005 6:10 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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mike wrote:
| Quote: | 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. |
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mike
Guest
|
| Posted:
Sat Mar 19, 2005 6:10 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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|
Bruce W.1 wrote:
| Quote: | 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
--
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/ |
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Active8
Guest
|
| Posted:
Sat Mar 19, 2005 6:10 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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|
On Sat, 19 Mar 2005 00:43:19 GMT, Bruce W.1 wrote:
| Quote: | 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 |
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Active8
Guest
|
| Posted:
Sat Mar 19, 2005 6:10 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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|
On Fri, 18 Mar 2005 14:58:25 -0800, mike wrote:
| Quote: | 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 |
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mike
Guest
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| Posted:
Sat Mar 19, 2005 10:34 pm Post subject:
Re: Device to open a circuit when a voltage is released? |
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|
Active8 wrote:
| Quote: | 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/ |
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Active8
Guest
|
| Posted:
Sat Mar 19, 2005 10:58 pm Post subject:
Re: Device to open a circuit when a voltage is released? |
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On Sat, 19 Mar 2005 08:34:05 -0800, mike wrote:
| Quote: | 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 :)
| Quote: |
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 |
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mike
Guest
|
| Posted:
Sun Mar 20, 2005 6:10 am Post subject:
Re: Device to open a circuit when a voltage is released? |
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|
Active8 wrote:
| Quote: | 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/ |
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Active8
Guest
|
| Posted:
Sun Mar 20, 2005 2:35 pm Post subject:
Re: Device to open a circuit when a voltage is released? |
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|
On Sat, 19 Mar 2005 17:30:06 -0800, mike wrote:
| Quote: | 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.
| Quote: | 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.
| Quote: | 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.
| Quote: | With -dV/dt cutoff, the most likely
|
Now I have a minus sign to ponder.
| Quote: | 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?
| Quote: | 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 |
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