[aprssig] NiCd Lessons relearned

KF4LVZ aprssigZbr6 at acarver.net
Fri Jul 14 17:33:13 CDT 2017


Not a surprise.  NiCds are supposed to be charged using a constant
current charger not a float voltage.  A smart charger will sense the
terminal voltage and alter the current profile at end-of-charge. Even in
a dumb charger that you have to remember to turn off (or just spend $10
and buy a wall timer if you're forgetful) they are supposed to be
constant current chargers.

If you charge at C/10  you don't need an end-of-charge test but the
charger must still be constant current and you still need to shut it off
after 16 hours or so.

You should also avoid charging your packs in series if you can.  Charge
the individual D-cells then put the pack back together.  You'll get
longer life from your pack because the cells will not charge equally
when strung in series.

On 2017-07-14 14:06, Robert Bruninga wrote:
> Lesson relearned on NiCd charging:  Several years ago I made three 12v batteries 
> from D cell NiCd’s.
> 
> They have been a huge disappointment.  They are only used once or twice a year 
> on critical field work and always fail far earlier than estimates.  But I always 
> just charge them the night before with a fixed voltage charge of 14 volts since 
> I most often forget about batteries I put on charge and end up ruining most of 
> them.  Charging at fixed voltage is safe…
> 
> For the AT Golden Packet event tomorrow, last night I left them on my usual 14 
> volt overnight charge and they were “fully charged” by morning, only drawing a 
> 50 mAh each in the morning at 14 volts..
> 
> Put them on a battery analyzer and their capacities came in at 10%, 8% and 3%.  
> Then the battery analyzer quick charged them at 1C rate for 1 hour with them 
> getting up to 16 or 18 volts, then a 4 hour equalization charge of 0.1C or 400 mA.
> 
> Then it retested them and got 75%, 65% and 85% of rated capacity!
> 
> So, Apparently little-used NiCd’s are not going to get a good charge from a 
> FIXED voltage charge!
> 
> Wish I had time to cycle them two more times.  On batteries at work we see huge 
> recoveries from little used NiCd’s when “rejuvenated” which is the 3 cycles of 
> charge and discharge I started with above.
> 
> Bob
> 
> 
> 
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