Subject:
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RE: Battery Charging Question
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 30 Mar 2000 00:43:20 GMT
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Original-From:
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Aaron Dwyer <AaronD@^antispam^nulec.com.au>
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Viewed:
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1864 times
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Ray
This is a post that Dennis Clark answered thoroughly for me just last week.
By the way thanks for that Dennis, I think I forgot to before.
In lugnet.robotics.handyboard, Aaron Dwyer <AaronD@nulec.com.au> writes:
> hi all
> the batteries are from mobile radios. motorola. 7.5V. 1200mAh.
> Nickel-Cadmium.
> can someone enlighten me on the best method to rejuvenate and charge these
> type of batteries are.
>
> motorola have a quick desktop charger available for $110, but i want to try
> it myself first.
You will need some good equipment, or you will need lots of patience and a
good DVM.
Here are the steps to rejuvinating old NiCds IF they can be recovered. If
they
have suffered the effects of overcharging (common) then they may not be
recoverable.
1. Discharge the pack completely at a C/10 or C/20 rate (60-120ma in this
case)
Complete discharge is considered to be .9V per cell. In a 6 cell (7.2V)
pack, this is 5.4V. WAIT FOR THE PACK TO COOL TO ROOM TEMP.
2. Charge them gently with a C/20 charger (C=1200mah in this case,
so C/20 is 60ma) until they are full. This is roughly 20 hours. The
pack
should be just slightly warm. Check on it from time to time, if it gets
hot before 20 hours are up (at 60ma) then you have a dead pack, recycle
it.
3. Do a high current discharge of 5 to 10Amps. A 1200mah pack is sub-c
cells
and they can handle that current easily. Discharge until the pack
reaches
.9V per cell, for a 6-cell pack, this is 5.4V. WAIT FOR THE PACK TO COOL
TO ROOM TEMP.
4. Do a high current charge of the pack until peaked. This is where you
need
the good equipment. You want to charge the pack at 3C at least
(3.6Amps).
This will take about 20+ minutes. You want a delta-peak detecting
charger
to do this - RC car chargers are designed to do this. If you decide to
do it by hand, then you have to put a volt meter on the pack. The
voltage
of a NiCd pack will rise as it is charging, so you need to provide a
constant current source to handle this. The pack is peaked when the
voltage
starts to drop. I use a peak charger, but I know that about .1V dropoff
is
not uncommon. An analog charger is best for this, watching the needle
and
noting its location is easier than tracking a digital readout. WAIT FOR
THE
PACK TO COOL TO ROOM TEMP. It will get a little warm during this
process,
if the pack gets hot, then then reduce the charge rate, and repeat steps
1-4, if it still gets hot, recycle the pack.
5. Repeat Step 3.
If the pack is recoverable, you should now have a decent NiCd battery
pack.
Yeah, its complicated and a mistake at any point in this process can
result
in a fire or explosion - I use a discharger that detects the proper cutoff
point and a delta-peak detecting charger that I can set the charge rate on
and
it tracks peak voltage and capacity. If your 6-cell pack has a peak voltage
over about 10.5V its a pretty crappy pack and not very good for high current
duties. You will need a power supply that is at least 12V to do this kind
of charging, and it has to handle about 5Amps to boot. Heat is the enemy,
NiCd's hate high temperatures.
have fun!
DLC
> -----Original Message-----
> From: Ray Tang [mailto:raytang_1@hotmail.com]
> Sent: Thursday, 30 March 2000 10:38
> To: lugnet.robotics.handyboard@lugnet.com
> Subject: Battery Charging Question
>
>
> Hi all,
> I was wondering if any battery expert can help me on
> this. A friend of
> mine gave me a NiMH battery pack for my HB expansion board
> AUX power supply.
> It is rated 6V, 3 AH (yeah, he gave me the spec.) but there
> is no charger.
> I know charging NiMH is complicated. I was wondering if
> anyone knows a
> ready-to-use charger circuit, or just the config of the
> charger, or some
> info on how I should charge it. Thanks!
> By the way, All Electronics (www.allelectronics.com)
> sells some cheap
> Nickel-Cadmium packs. Some of them are 6V at 600 mAH for about $5.00.
>
> --
>
> Ray
--
Aaron Dwyer PH +61 7 3249 5635
Systems Engineer FAX +61 7 3249 5888
Nulec Projects http://www.nulec.com.au
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Message has 1 Reply:
 | | Re: Battery Charging Question
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| Hi, Yes, I read that too. But the pack was NiCd, mine is NiMH. According to some people, the charging methods between the two are different. I don't think I can charge NiMH pack like a NiCd pack (or can I??). -- Ray Aaron Dwyer (...) (25 years ago, 30-Mar-00, to lugnet.robotics.handyboard)
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