OT - Ever Build a Battery Load Tester?
 

Has anyone ever built a homemade battery load tester? It doesn't seem like it should be hard to do, but I'm more of a mechanical guy. If anyone has plans for one, please share. Hauling batteries around to be tested is a pain.

Thanks,
Jeff

jgmr1

I would think that a volt-ohm meter or multimeter in parallel (across) a 55 watt rated head light would make a sufficient tester. Alligator clips on leads to the head light socket to attach to the battery.

Otherwise, if you have an accessory socket just insert an accessory plug with the leads connected to the multimeter. Turn on the ignition switch and make sure the head light is on. Check the voltage. It should be at least 12 volts, closer to 13 volts if memory serves. Perhaps one of the other Forum Members can provide a more definitive value. But that's about all it takes.

If the battery voltage droops below about 11.8 volts under a 55 watt or greater load (without the engine running) then I'd say you have a weak cell. Time to replace the battery.

(Based on 6 cells in a battery providing 2.3 volts each for a total of 13.8 volts in perfect condition. 5 good cells approx = 11.5 volts plus some small voltage from the weak cell.)

Will give you no idea if it will hold up under starter load though.

You need to construct a non-destructing/incendiary 100A load, at iminimum, ideally 125A for these big twins.

Tons of lightbulbs are the easiest way, seriously,

Assuming you create a load of 100A, what should the voltage decay curve look like for a good or bad battery?

Our automobile battery load test was 250 amps for 10 seconds, if voltage fell below 9.6. charge & re-test. This is minimal and for used batteries. THe load was adjustable.
At present I use a Snap-On hand held unit that applies a fixed but unknown load. But it also brings a good battery to 10 volts real quick. Even fully charged loser batteries go below the scale instantly.

Jim

Jeff
or go to ebay and one of these
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=4564524990&category=43 989&rd=1
or one of these;
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=4563064176&category=43 989&rd=1
accurate testing of a battery requires a load proportional to the capacity of the battery, or you could also get a fixed load device for ten to twentyfive dollars, I think going to ebay would be easier and cheaper in the long run, I might even have an old one in the basement to get rid of. you can get used old professional grade equipment prety cheap, and you might even be able to sell it for close to what you had in it

chuck