OT: NiCad batteries - AAA size
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Posts: 46,084
Sid,
An other thing to consider is the electrolyte of Ni-Cd is potassium hydroxide
dissolve in water and absorbed by
porous stuff. So, after a full charge, the next
thing of a continuiting current flow does to the cell is to electrolysing the
water in
hydrogen and oxigen which will "dry" the cell. You can see the effect of that
by compare the voltage difference across the battery while applying different
current from .5 A. to 1.5 A. If you have a difference voltage of 2 volts, then
the inner resintance of the cell is R=V/I, 2=2/1 then this resistance in then 2
ohms
which is for a weak cell. This inner resistance might not exceed 0.3 ohm for a
small cell (AAA) and .12 ohm for a D size. So the smallest the difference
voltage the better the battery is. This is also the reason why a weak cell of a
video camera battery seem to be charged faster on the SONY charger than a
good one, simply because the weak one will reach faster the threshold voltage
of the battery charger's monitor , because of it high resistance, than the brand
new one.
Rene
Newzed@a... a
An other thing to consider is the electrolyte of Ni-Cd is potassium hydroxide
dissolve in water and absorbed by
porous stuff. So, after a full charge, the next
thing of a continuiting current flow does to the cell is to electrolysing the
water in
hydrogen and oxigen which will "dry" the cell. You can see the effect of that
by compare the voltage difference across the battery while applying different
current from .5 A. to 1.5 A. If you have a difference voltage of 2 volts, then
the inner resintance of the cell is R=V/I, 2=2/1 then this resistance in then 2
ohms
which is for a weak cell. This inner resistance might not exceed 0.3 ohm for a
small cell (AAA) and .12 ohm for a D size. So the smallest the difference
voltage the better the battery is. This is also the reason why a weak cell of a
video camera battery seem to be charged faster on the SONY charger than a
good one, simply because the weak one will reach faster the threshold voltage
of the battery charger's monitor , because of it high resistance, than the brand
new one.
Rene
Newzed@a... a
Comments
battery should be allowed to discharge to? What is the max voltage it can be
overcharged without damage?
Thanks
Sid Weaver
[noparse][[/noparse]Non-text portions of this message have been removed]
If you have an empty NiCd cell which shows 1.0 Volt (with no
discharge current applied) the it is really empty. Most NiCd cells
recouver a bit after (fast) discharging and go up again to 1.1 or
sometimes 1.2 Volts.
So, from the Voltage you can't really tell how "empty" your battery
is.
Charging a NiCd cell the voltage goes up to about 1.4 Volts, but
different brands may have different voltages.
One way to see when a NiCd cell is fully charged is its temperature.
Another way is to determine a small but fairly sudden drop in battery
voltage when the cell is fully charged (in Europe called the delta-U
method).
I use the temperature criterium set at 8 degree C above
roomtemperature and that gives quite the same results as the voltage
drop criterium. With NiMH batteries I use a temperature limit that is
a bit higher than with NiCd cells.
I hope this helps.
Regards,
Klaus
PS is it really that off topic as we all use these battery's and want
to get the most out of them?
Oorspronkelijk bericht
Van: Newzed@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=IIX02NWfGGUnnpcG1CGOLA2f1S55bJg-INgK0zYt1gbdAQD6YTWiMG5xvd_JJvvkuMuWbeuHTRg]Newzed@a...[/url
Verzonden: dinsdag 13 januari 2004 21:36
Aan: basicstamps@yahoogroups.com
Onderwerp: [noparse][[/noparse]basicstamps] OT: NiCad batteries - AAA size
Does anyone have any specific information on the lowest voltage a
NiCad
battery should be allowed to discharge to? What is the max voltage
it can be
overcharged without damage?
Thanks
Sid Weaver
> [noparse][[/noparse]Non-text portions of this message have been removed]
klausdejong@x... writes:
> So, from the Voltage you can't really tell how "empty" your battery
> is.
>
> Charging a NiCd cell the voltage goes up to about 1.4 Volts, but
> different brands may have different voltages.
>
Thanks, Klaus
i am charging to NiCad AAA in series, and the circuit has been very tricky.
After "fine tuning" the charge time vs the time it was discharging into the
ADC, I finally got the batteries to charge up to 2.418, chich is about as close
as you get to full charge - I guess. I can detect no change in batt temp
when it is charged. I have let in sit in the circuit for 2 to 3 hours, the
voltage never goes over 2.418 and the batts never get warm. So I assume what I
doing is OK. If I remove the battery from the circuit it drop to about 1.15
very
quickly.
if I leave it in the circuit, but turn the circuit off, overnight the batt
will drop to about .90 volts.
It is being charged by a circuit which turns an opamp on and off, with the
opamp charging the batt via a 270 ohm resistor. During the off periods the
voltage is read be an ADC and plotted on Stamp Plot to show the charging
is progressing.
Sid
[noparse][[/noparse]Non-text portions of this message have been removed]
From what you tell about the behaviour of you NiCad cells and the
nature of your charger my feeling is that your battery is just not
fully charged.
Charging through a 270 Ohm resitor at a voltage of say 12 Volts
(typical opamp power supply :-) before the resistor and AAA cells
having a capacity of say 350 mAh I would estimate you would need a
charging time of 12 to 14 hours. A charged cell will, once
disconnected from the charger, have up to about 1.35 Volts per cell
and then drop a bit to 1.30 or 1.25 Volts. Most power comes out at
about 1.2 Volts, the cell stays there for quite a while and then
suddenly drop to below 1.0 Volt. The last few mAh's come out then.
From my experience I can not recommend to discharge a cell below 0.80
Volts as this can lead to a permanent loss of capacity.
Take a look closer at your figures. What you tell sounds a bit
strange to me.
Tip: if you havent done yet put a diode between your charging circuit
and the cells to be charged. It will prevent the battery to discharge
through your charging system.
Succes,
Klaus
> Thanks, Klaus
>
> i am charging to NiCad AAA in series, and the circuit has been very
tricky.
> After "fine tuning" the charge time vs the time it was discharging
into the
> ADC, I finally got the batteries to charge up to 2.418, chich is
about as close
> as you get to full charge - I guess. I can detect no change in
batt temp
> when it is charged. I have let in sit in the circuit for 2 to 3
hours, the
> voltage never goes over 2.418 and the batts never get warm. So I
assume what I
> doing is OK. If I remove the battery from the circuit it drop to
about 1.15 very
> quickly.
> if I leave it in the circuit, but turn the circuit off, overnight
the batt
> will drop to about .90 volts.
>
> It is being charged by a circuit which turns an opamp on and off,
with the
> opamp charging the batt via a 270 ohm resistor. During the off
periods the
> voltage is read be an ADC and plotted on Stamp Plot to show the
charging
> is progressing.
>
> Sid
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
goflo@p... writes:
> Instantaneous cell voltage during constant-current charge is not a
> particularly good indicator of battery charge - A typical recommend-
> ation is to monitor cell voltage, temperature, and charging time,
> terminating chg when the OCV "droops", temp begins to rise at a given
> rate, or max chg time is reached - Or some combination thereof.
> These characteristics typically get harder to distinguish as cells age,
> so an ideal charger would monitor the chg-dischg cycle and "learn" the
> regimen most suited to the battery and app.
>
The charging circuit I'm using with Stamp Plot tells me when 2 AAA in series
reach 2.418 volts. I consider the circuit in equilibrium when this value
remains steady over a long period of time. The batts are charged, charging
current turns off, voltage monitored with an ADC, charging resumes. This cycle
is
continued until the ADC indicates a pre-determined count has been reached,
indicating batt is charged. The batt voltage is constantly monitored and if
voltage drop 2 counts on the ADC, charging is resumes. The trick to the circuit
was getting the battery to 2.418, then to balance the
charge on/charge off periods so the battery always indicated 2.418 volts.
Believe it or not, this timing was critical to with 10ms. If the charge was
off, the batt drained back into the opamp that was charging it - a very small
drain, but still a drain - so I had to charge it just enough to offset this
drain.
Once equilibrium is achieved I let it sit on the charger for about an hour to
mnake sure it was fully charged. This is the only way I have.
However, I'm going to look into the temperature thing. I can strap an LM34
to the batteries and read the LM just after I read batt voltage. The LM34 is
very sensitive and perhaps this will tell me something. Nothing ventured -
nothing gained, you know.
Sid
[noparse][[/noparse]Non-text portions of this message have been removed]
klausdejong@x... writes:
> From what you tell about the behaviour of you NiCad cells and the
> nature of your charger my feeling is that your battery is just not
> fully charged.
>
How high can I let the instantaneous voltage reading go - 2.4375, 2.4750,
2.50 ??
Sid
[noparse][[/noparse]Non-text portions of this message have been removed]
- Individual - NiCd and NiMH cella can be safely discharged to 0 V
before recharging, although the amount of current the cell will
supply below 1 V is very small. Some claim that periodic "deep"
discharge of NiCds is beneficial.
Battery packs should not be discharged below .9 to 1 V across the
weakest cell - The stronger cells will reverse-charge the discharged
cells, damaging them irreversibly. I've seen a lot of "bad" battery
packs with one expired cell, the rest seemingly usable - This is why.
Instantaneous cell voltage during constant-current charge is not a
particularly good indicator of battery charge - A typical recommend-
ation is to monitor cell voltage, temperature, and charging time,
terminating chg when the OCV "droops", temp begins to rise at a given
rate, or max chg time is reached - Or some combination thereof.
These characteristics typically get harder to distinguish as cells age,
so an ideal charger would monitor the chg-dischg cycle and "learn" the
regimen most suited to the battery and app.
regards, Jack
Newzed@a... wrote:
>
> Does anyone have any specific information on the lowest voltage a NiCad
> battery should be allowed to discharge to? What is the max voltage it can be
> overcharged without damage?
energy is transformed to heat. So that is the point where the battery
is charged. Voltage of the two will be something like 2.6 to 2.8
Volts.
Klaus
--- In basicstamps@yahoogroups.com, Newzed@a... wrote:
> In a message dated 1/13/2004 6:10:31 PM Eastern Standard Time,
> klausdejong@x... writes:
>
>
> > From what you tell about the behaviour of you NiCad cells and the
> > nature of your charger my feeling is that your battery is just
not
> > fully charged.
> >
>
> How high can I let the instantaneous voltage reading go - 2.4375,
2.4750,
> 2.50 ??
>
> Sid
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
a constant voltage source like dry cells and lead acid batteries do. You can
not properly charge them by charging to a certain voltage. Each
manufacturer, model and even individual NiCd cells will have different
maximum voltages when charged.
If the voltage goes to a certain voltage and never changes you are either
using too low of a voltage or too low of a current.
Most modern AAA NiCad cells (Sanyo or Gold Peak) can be charged at up to 1
amp. You have to monitor the voltage and when it falls about .02 volts per
cell (or in your case .04 volts for two cells) you should be very close to
fully charged... the peak voltage DOES NOT matter. As was stated before, you
can also monitor the temperature of the cells, but this temperature increase
also depends on what amp rate you charge the batteries at.
Some NiCd battery charger circuits can be found at
http://www.meridianelectronics.ca/gadgets/carnc12.htm
http://www.meridianelectronics.ca/gadgets/ccharger.htm
http://jaichi.virtualave.net/lade-e.htm
http://www.capable.ca/rcstuff/fastchg.htm
http://www.capable.ca/rcstuff/charger.htm
Hank Hagquist
HobbyTalk - http://www.hobbytalk.com
HobbyShopper - http://www.hobbyshopper.com
Original Message
From: <Newzed@a...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, January 13, 2004 5:54 PM
Subject: Re: [noparse][[/noparse]basicstamps] Re: OT: NiCad batteries - AAA size
> In a message dated 1/13/2004 5:18:34 PM Eastern Standard Time,
> goflo@p... writes:
>
>
> > Instantaneous cell voltage during constant-current charge is not a
> > particularly good indicator of battery charge - A typical recommend-
> > ation is to monitor cell voltage, temperature, and charging time,
> > terminating chg when the OCV "droops", temp begins to rise at a given
> > rate, or max chg time is reached - Or some combination thereof.
> > These characteristics typically get harder to distinguish as cells age,
> > so an ideal charger would monitor the chg-dischg cycle and "learn" the
> > regimen most suited to the battery and app.
> >
>
> The charging circuit I'm using with Stamp Plot tells me when 2 AAA in
series
> reach 2.418 volts. I consider the circuit in equilibrium when this value
> remains steady over a long period of time. The batts are charged,
charging
> current turns off, voltage monitored with an ADC, charging resumes. This
cycle is
> continued until the ADC indicates a pre-determined count has been reached,
> indicating batt is charged. The batt voltage is constantly monitored and
if
> voltage drop 2 counts on the ADC, charging is resumes. The trick to the
circuit
> was getting the battery to 2.418, then to balance the
> charge on/charge off periods so the battery always indicated 2.418 volts.
> Believe it or not, this timing was critical to with 10ms. If the charge
was
> off, the batt drained back into the opamp that was charging it - a very
small
> drain, but still a drain - so I had to charge it just enough to offset
this
> drain.
> Once equilibrium is achieved I let it sit on the charger for about an hour
to
> mnake sure it was fully charged. This is the only way I have.
>
> However, I'm going to look into the temperature thing. I can strap an
LM34
> to the batteries and read the LM just after I read batt voltage. The LM34
is
> very sensitive and perhaps this will tell me something. Nothing
ventured -
> nothing gained, you know.
>
> Sid
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
>
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I have a system running that just does the thing you want.
I use the PCF8591 as a 4 channel ADC to measure battery voltage,
charge and discharge currents and battery temperature. It uses the
analog output from the PCF to control the charge current via a LM317
and one output from a TDA8444 to control the discharge current.
I get a graphical display of voltages and currents vs time. I also
get the total amount of mAh's which go _in_ or _out_ the battery. In
this way I can see the (dis)charging cycles on my screen.
There also is a feature built in to measure te maximum capacity of a
battery. It then first charges until the "full" criterium is reached
en then fully discharges. The amount of mAh's that comes out then is
the capacity of the cell. After that the battery is charged again, of
course. It is amazing to see how the capacity of some brands drops
over time or if there a battery had a deep discharge.
But....., this thing is from my "pre-Stamp-era" so it is running on a
PC. But I'm shure you can build this in a Stamp BS2p fairly easy as
it supports the I2C bus of the PCF and the TDA. The graphic's work
will still be done by the PC.
It is a nice and helpfull system to have, I can always see how the
proces is going and I feel like a blind man if I have to charge a
battery without these features.
So, the big challange is to put such a system to work on a Stamp :-).
Regards,
Klaus
--- In basicstamps@yahoogroups.com, goflo@p... wrote:
> It'd be interesting to discharge the battery at a controlled
> rate, track the process with Stamp Plot, then use the data to
> optimize the charge cycle to battery capacity.
>
> Jack
>
> Newzed@a... wrote:
> >
> > In a message dated 1/13/2004 5:18:34 PM Eastern Standard Time,
>
> > The charging circuit I'm using with Stamp Plot tells me when 2
rate, track the process with Stamp Plot, then use the data to
optimize the charge cycle to battery capacity.
Jack
Newzed@a... wrote:
>
> In a message dated 1/13/2004 5:18:34 PM Eastern Standard Time,
> The charging circuit I'm using with Stamp Plot tells me when 2 AAA in series
> reach 2.418 volts. I consider the circuit in equilibrium when this value
> remains steady over a long period of time. The batts are charged, charging
> current turns off, voltage monitored with an ADC, charging resumes. This
cycle is
> continued until the ADC indicates a pre-determined count has been reached,
> indicating batt is charged. The batt voltage is constantly monitored and if
> voltage drop 2 counts on the ADC, charging is resumes. The trick to the
circuit
> was getting the battery to 2.418, then to balance the
> charge on/charge off periods so the battery always indicated 2.418 volts.
> Believe it or not, this timing was critical to with 10ms. If the charge was
> off, the batt drained back into the opamp that was charging it - a very small
> drain, but still a drain - so I had to charge it just enough to offset this
> drain.
> Once equilibrium is achieved I let it sit on the charger for about an hour to
> mnake sure it was fully charged. This is the only way I have.
>
> However, I'm going to look into the temperature thing. I can strap an LM34
> to the batteries and read the LM just after I read batt voltage. The LM34 is
> very sensitive and perhaps this will tell me something. Nothing ventured -
> nothing gained, you know.
Are you talking about Nickle-Cadmium Nicads or are you referring to
Nickle-Metal-Hydride batteries (NMH)? A lot of people tend to confuse
the two battery types. But they have different charge discharge
requirements.
Under a load you should stop discharging or using a Nicad cell at 1.1
volts. After 1.1 volts is reached they start to drop off very rapidly,
below 1 volt could result in them being damaged so that they may or may
not hold a charge well or become weak and loose capacity.
The maximum voltage is a little over 1.2v. You can get a lot more info
about this from the RC racing car people, as they have it down to a very
fine science.
Original Message
From: Newzed@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=7zcDed6p8dwhNPMdAUWjrLG1UNb7lJXhFVu84RSywF3kRbcL9fBr1I8D0hUP1H-j8GSVsTT3]Newzed@a...[/url
Sent: Tuesday, January 13, 2004 2:36 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] OT: NiCad batteries - AAA size
Does anyone have any specific information on the lowest voltage a NiCad
battery should be allowed to discharge to? What is the max voltage it
can be
overcharged without damage?
Thanks
Sid Weaver
[noparse][[/noparse]Non-text portions of this message have been removed]
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