Electrathon America Forum

spacegy4 · Newbie

Testing electrical system

bd64 · Senior Member

If you want to use lamps for battery testing, an old seal beam headlight will draw about 4 amps on high beam. You will likely need ten to get around 40 amps. This light bank makes for a pretty good student project. If you would like something that is easier you can use your car for both battery testing and electrical check by removing the leads from your motor and attaching extension wires with about 15 inches of .035 welding wire as an element. This element needs to be placed into a bucket containing about 4 gallons of water -- ad hotdogs if you wish --. Use the the throdle of the car to draw whatever load you wish but be sure to run over 1/2 pot or your controller will likely get hot.

Date: Jun 23, 2010

Be sure the connections are solid or you get problems later with your electircal system on the car if you do the water heater test.

bd64 · Senior Member

Yes, What he said, it can cause some difficulties.

Kyle Keenan · Veteran Member

Connections are key, we actually had a student melt the post off of a tractor battery we were using to get our wiring diagram figured out. He just had them "touching" and blam, away it went.

Kirk Swaney · Veteren Racer

For testing the bat meter you asked about and system for reliability and functionality...

The simplest and usually "accurate enough" method we use is to compare the voltage and amperage readings of the in-car meter(s) to readings of two external measurement tools.

For "external" measurement comparison tools we prefer a hand-held clamp meter for current and a multimeter for measuring voltage. The other calculations your battery meter will make are usually based off these two, so confirming them covers Amp-Hours, Watts and other meter data produced.

If possible, test & confirm while the system is running under the load that you most care about. For Electrathon and similar event power allowances, that's around 35-40 amps. Also, measurements will be more stable and easier to compare if using a non-motor load such as the light panel or a big resistor. For a steady throttle position, remove the throttle return spring (if it's safe to do so) or plug-in an external potentiometer located where the person running the test can easily reach and adjust. An unprotected pot is about $2 at Radio Shack.

The external measurement tools should be sensing from the same place in your car as the in-car power monitor(s) that they will be confirming. This is to avoid "actual" differences in readings.

As others have posted, those sneaky loose connections can be a serious energy hog. The same is true if you are running jumper cables for any of the confirmation testing described above - if one measurement device goes through the jumpers and the other device does not. If you're wondering about loose connections see how to find loose connections on your car.