Finish charging AGMs

["BillDube@killacycle.com" <BillDube@killacycle.com>]

 >I still bracket race the current eliminator most every weekend from 4 to 10
 > qt. mile runs.I bulk charge after each run and time permiting
 >try to finish charge with my seperate regulator system.Batteries are also
 >being cooled while chargeing.OCV after most runs=12.75 with max.end of day
 >temp of 145F.Question do I charge as above after the last run or do I
 >wait till the next day when the pack has cooled.

	It all depends on the battery chemistry you are using and the nature of 
the finish charge.

	Let me assume you are using AGM lead-acid batteries.

	It's best if all the batteries are the same temperature. Finish charging 
of nearly any sort will increase the temperature, so it would be prudent 
not to be at 145 F which is the max allowable temperature for batteries 
with plastic cases that get too soft above this temperature. These two 
factors suggest that you should let the pack cool overnight and then fish 
charge after the pack has cooled to room temperature.

	Thermal runaway also needs to be considered. A hot battery will enter 
thermal runaway quite easily. That is, a battery (or a cell within a 
battery) will heat up and will start to conduct very very well. The more it 
heats, the better it conducts, and the more wattage it draws. Under a bulk 
charge of a hot pack, I have had this happen at constant current, which is 
very unusual, but not unheard of. It typically happens under constant 
voltage charge of a hot battery.

	The risk of thermal runaway also suggests that you wait until the next day 
(when the pack is cool) to perform the finish charge.

	I typically cycle the pack the evening before a race and perform a finish 
charge the last thing. The next morning, just before the race, I finish 
charge the pack again, both to warm it up and to make sure that I have 
crammed every possible amp-hour into it.

 >>> Best method for finish charge of AGM batteries <<<<<<<<

	For Optima YellowTops, T H E best finish charge is 3 amps delivered for 
about an hour pulsing 15 seconds "on" and then 15 seconds "off". For 
smaller batteries with thinner separators, the cycle frequency should be 
increased and the current reduced. For 16 A-hr Hawkers, the charge should 
be modified to something like 5 seconds on and 5 seconds off with a 1 amp 
constant current charge.  This is the best way to fully charge the negative 
plate (which tends not to get fully charged using less aggressive charging 
methods.)