Re: (ET) Trying 29 cells for BB600

["David Roden" <etpost drmm net>]

On 16 Apr 2023 at 14:27, Chris Zach via Elec-trak wrote:

> One solution I tried was modifying the ballast capacitor in the charger, 
> but
> when my timer failed on my E15 I nuked a complete string of 30 cells 
> into a
> solid block of plastic and nickel. On the positive side, it did have a 
> lot
> more capacity. Well until it melted.

To get the most out of that battery, you really need a smart charger with 
the correct profile.  But I've been saying that for years and obviously I 
haven't convinced you.  :-)

An unmodified ET factory charger isn't just mostly dumb, it's the wrong 
kind of mostly dumb for a NiCd battery.  It charges at a regulated 
voltage, 
not a regulated current.

You can safely charge NiCd batteries almost indefinitely with a constant 
current charge of 0.1C, where C is the C20 amp hour capacity expressed in 
amps.   Voltage doesn't matter much, only current, though watching for the 
on-charge voltage to fall (negative dv/dt) is a great way for an automatic 
NiCd charger to decide when to shut off.

So if your battery is (say) 34 ah at 20h, you can charge it at a regulated 
current of 3.4 amps. 

If charged at 0.1C your NiCd battery will take about 10-12 hours to reach 
full charge from flat.  So you can set a shutoff timer for 10-12 hours.  
If 
the battery isn't flat when you start the charge and thus gets overcharged 
by 25% or 50%, it's no big deal at that current.  If the timer fails on, 
and you don't remember to check it for a few days, again, no big deal.


David Roden - Akron, Ohio, USA

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