500 Amp Battery Load Tester

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One of the best ways to evaluate the condition of a lead-acid battery is to load test it. The best load testers allow applying variable but heavy loads to the battery while observing the terminal voltage.

Someone on the EVDL mentioned this battery tester awhile back. I looked around and found a good price at amazon.com, I think. Obviously, the first thing any good geek does is take the new gadget apart and take photos. These pictures are what resulted.

For the money, this is a nice tester. The carbon pile is a little small and has a large temperature coefficient. This means you have to "ride the gain" to maintain a given amperage. The end-of-test buzzer is a bit wimpy. The unit gets fairly hot. Other than that, it works well.

Batteries tested since 05/23/07

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Here is the tester. This same unit is private labeled with several major brands. This unbranded unit was the cheapest.

Here is the inside. The carbon pile is lower center. The fixed resistors are on either side of the pile. The green PCB is the test duration timer. The current shunt is right below the right hand meter.

This is a shot looking down on the pile. It's construction is apparent. As the carbon discs in the pile are squeezed harder by the threaded knob on the front its resistance decreases. The pile is, in effect, a big variable power resistor.

Another shot of the pile and the fixed resistors.

This shot shows the current shunt. It ain't precision but it does work.

Here is a close-up of the pile.

A view of the top of the pile. The setting screw has been loosened enough to provide clearance between the top disc and the terminal piece.

A closeup of the alarm timer board.