Re: Multiple lead-acid charging

Roy wrote:
<snip statement that charger needs to be matched to battery AH>

 > I don't undertsnad you };)

Ok. Take a modern multi-stage charger designed for batteries in the 
range 100 -200AH and connect it to a flat 400 AH battery.

It will start to charge on constant current, with the charger monitoring 
battery voltage. There is a microprocessor in the charger that has been 
programmed to measure the time it takes for the battery voltage to rise 
to a predetermined level.

Also programmed into the charger is a time limit.  Based on the maximum 
battery size (200AH) the voltage should always rise to the limit within 
  x hours. So the limit is set at, say,  x+5 hours. If that limit is 
exceeded, the microprocessor treats it as a fault and sounds an alarm 
and stops the charging process. It does this because the designer does 
not want the charger to keep "charging" a faulty battery - something 
that could easily lead to large quantities of explosive gases being
vented.

However, if such a charger is placed on a much bigger battery than the 
designer intended, say a 1000AH battery - then problems arise. The 
charger still charges, but the x+5 hours programmed into it is exceeded. 
  The charger treats a battery much larger than its design specification 
as a faulty battery. It isn't and, without that time limit, the charging 
process would continue both safely and to completion. However, the 
charger safety programming won't allow it.

But, all that is needed is a simple firmware patch, to change x to y. eg 
change 20 hours to 50 hours. Many manufacturers will do that for a small 
charge (often, IME, for no charge at all).  Firmware is usually stored 
in a removable chip and they can supply a replacement chip, programmed 
with the new limit. The owner/maintainer simply swaps the chip.

These are, of course, big specialist chargers costing many hundreds of 
pounds and whose manufacturers have a design and sup****t team.
If you buy an off the shelf 20A charger for £60 - don't expect that sort 
of sales sup****t..

--
Sue