> Is the 15V an absolute value, or should it be compensated to some > reference temperature (and if so, what is the appropriate reference > temperature)?
The Optima approved gassing/absorbtion voltage from the back of the Zivan NG3 manual is; 2.5 vpc until 10C (15v per block) tapering by 2.5mv per degree to a maximum temperature of 50C (14.4v per block). One of the problems is that the temperature sensor needs to be mounted up one of the holes in the bottom of the battery pressed firmly against the centre two cells, this being the hottest area of the battery (I was informed that on top of the battery was fine). Another problem is that you don't know at any given time which is your hottest battery. This problem gets worse with increasing string length, but even Cedric Lynch has had the problem with his 48volt pack. As per my recommendation he turned his NG3 down a little and cured the problem. Some people use a very conservative voltage rating and let the current taper away well below 1 amp, letting time rather than high voltage get the batteries fully charged. A similar procedure is actually recommended in the Hawker EV handbook. I have an extra connector hooked up so I can put my pack on my big variac. After a couple of days on float I can get the batteries to 16.5v at just 200mA. When I finally got to talk to JCI about my battery problems they asked me to do a charge of 500mA for 48 hours. I noticed a big improvement in capacity at 20 amp, but much less at 55 amp. Paul Compton BVS technical officer www.bvs.org.uk www.sciroccoev.co.uk
