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NiCads

 
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alexpeterson(at)earthlink
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PostPosted: Sun Mar 19, 2006 6:17 pm    Post subject: NiCads Reply with quote
Years ago, I knew an electrical engineer who claimed he could rejuvenate
NiCad batteries by charging a capacitor and zapping it across the battery.
I watched him do this, and saw what I recall were positive results. He
claimed it reduced the internal resistance, so they would hold a charge
better. Is there anything to this?


Alex Peterson
RV6-A N66AP 729 hours
Maple Grove, MN

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rv-9a-online(at)telus.net
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PostPosted: Sun Mar 19, 2006 6:50 pm    Post subject: NiCads Reply with quote
I've done it a lot. I used it to blow out internal shorts in battery
packs. I'd take a big computer-grade low esr electrolytic, charge it
with a power supply then connect it to the batter pack.

The large current would blow out any internal shorts.

This works a few times, but is not a permanent fix for NiCd problems.

Also, the charge rate of NiCd batteries is proportional to the discharge
rate... so the trick is to discharge them quickly, then charge them
quickly using special chargers (battery charger/conditioners).

Also, it's better to pulse charge the NiCd batteries, rather than using
a smooth DC charging source.

You may want to Google it, because there is a lot of info available.

Vern Little

Alex Peterson wrote:
Quote:


Years ago, I knew an electrical engineer who claimed he could rejuvenate
NiCad batteries by charging a capacitor and zapping it across the battery.
I watched him do this, and saw what I recall were positive results. He
claimed it reduced the internal resistance, so they would hold a charge
better. Is there anything to this?


Alex Peterson
RV6-A N66AP 729 hours
Maple Grove, MN



















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brian



Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA
PostPosted: Sun Mar 19, 2006 7:18 pm    Post subject: NiCads Reply with quote
Alex Peterson wrote:
Quote:


Years ago, I knew an electrical engineer who claimed he could rejuvenate
NiCad batteries by charging a capacitor and zapping it across the battery.
I watched him do this, and saw what I recall were positive results. He
claimed it reduced the internal resistance, so they would hold a charge
better. Is there anything to this?

There is something to this but it is not because it reduced the internal
resistance.

Seems that NiCds have a tendency for the sodium hydroxide electrolyte to
form conductive crystals if the battery is left discharged. The crystals
grow through the separator and cause a short between the plates
(electrodes inside the battery). When that happens you can't charge the
NiCd.

What the capacitor does is provide a huge momentary current that
destroys these crystals without overheating the battery. Once the shorts
are blown clear, the battery will then take a charge.

The only caveat is, when this happens it usually means that the battery
is approaching the end of its life. The crystal is not completely
destroyed but the short is removed. The crystal is likely to grow back
and short the cell again. Still, it is a useful technique if you need to
get a couple more cycles from your NiCds.

--
Brian Lloyd 361 Catterline Way
brian-yak at lloyd dot com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

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+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery
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