Re: (ET) Trying 29 cells for BB600

["David Roden" <etpost drmm net>]

On 16 Apr 2023 at 17:52, Chris Zach via Elec-trak wrote:

> these things need to be hit with a lot of current right out of the box. 

I've seen that behavior with some lead batteries, notably the old Hawker 
Genesis AGMs.  I haven't noticed it in flooded NiCd batteries, but my 
experience was with Saft STM5-100 monoblocks, not your BB range cells.

> What *would* work would be something that could go in-line with the
> Elec-trak's charger to regulate the peak voltage and current coming
> out of those rectifiers. 

Yeah, I've suggested that before - at least a little bit of outboard 
smarts 
added onto the blunderbuss GE charger. Current regulation to make it an 
adjustable constant current charger would at least help.

> Flooded NiCDs are not the same as sintered plate. 

I don't know about your BBs, but all of Saft's flooded railroad / aircraft 
/ EV batteries that I'm familiar with had / have sintered positives and 
plastic-bonded negatives.

Here it is in a current product:

http://davidsonsales.com/public/pdfs/SAFT%20NiCad%20Battery%20Brochure.pdf

or https://v.gd/2ZvTfC

> What worked for those big SAFT 6 volt cells in the old days?

They weren't 6 volt cells.  No such critter in NiCd clothes is possible; 
cells are always 1.2 volts nominal.  However, at one time Saft made nice, 
chunky 180 AH 6 volt 5-cell monoblocks about the size of golf car 
batteries, designated STM5-180.

Here are the charging instructions.

"In cycling applications, STM batteries are preferably charged in a 
constant current mode at current rates between 27 A and 36 A ...

"The battery is charged in a first step at constant current, with 
increasing battery voltage.  As soon as the predetermined charging voltage 
has been reached, the battery is charged in a lower current in order to 
avoid ineffective battery heating during the necessary overcharge.  [...]

"First step: high rate charging at 0.2C [36 amps] up to predetermined 
threshold voltage.

"Second step: low rate charging at 0.04C [7.2 amps] without voltage 
limitation.

"The charging time of the second step is the same as the charging time of 
the first step.  The resulting charge coefficient is 1.2.

"Maximum charging time of a fully discharged battery is 10 hours.  For new 
batteries, it could be 11 or 12 hours. [...]

"The predetermined threshold voltage at the end of the first charging step 
is 1.6 volts per cell at 20 deg C. [...]

"Temperature coefficient: -0.004 v per deg C per cell."

http://evdl.org/docs/STM5-180tech.pdf


David Roden - Akron, Ohio, USA

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