Re: (ET) re: battery testers

["David Roden (Akron, Ohio, USA)" <roden ald net>]

From:                   "Wombat" <Wombat RealNS com>

> The
> generally assumed correct test is to load the battery at some level until
> its voltage drops to 10.5 volts.  The resultant time is its capacity.
> 

Correct.  Just a few more notes regarding this.

Typically golf car batteries are measured for their minutes of "reserve 
capacity" (RC) at 75 amps. 

You would need to connect 3 headlights in series for a 36 volt pack.   
Then you would have to parallel enough trios of headlights to reach 75 
amps.

There are other ways to create loads.  One (somewhat risky) one is to 
fill up a large bucket with water and plunge in heavy conductors.  Raise 
or lower the conductors to change the load.  Some people add salt to the 
water to change the resistance (don't breathe the gas that is evolved if 
you do this).

Another way is to use one or more paralleled electric water heater 
elements of appropriate size in a large bucket of water (this works 
better with the higher voltage packs used in road EVs, however).  

And yet another is to use multiple electric space heaters with the 
elements paralleled and connected to the pack, and the fans wired 
separately to run on the AC line.

Testing is a miserable task on a 98 degree day -- a load bank mounted 
outside the garage makes it more bearable.

10.5 volts is the discharged voltage specified (under load) for a 12 volt 
battery.  For our 6v GC  batteries, it's half that amount.  

The most common golf car batteries used (T-105 or US 2200 type, 220 amp 
hours at the 20 hour rate) are rated for around 105 minutes RC.  A 
battery is considered to be at the end of its useful life when it can no 
longer produce 80% of its specified reserve capacity.  

FWIW, the usual reserve capacity spec for most 12v deep cycle batteries 
is at 25 amps, not 75.


David Roden - Akron, Ohio, USA
1991 Solectria Force 144vac
1979 General Engines ElectroPed 24vdc
1974 Honda Civic 96vdc
1970 GE Elec-trak 36 vdc