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For years, I’ve used an old automobile headlight to test batteries and power supplies. Actually, it’s the high-beam filament – this is the bulb that was replaced when the low-beam filament burned out. It draws about 5 amps, and has an obvious indicator that everything is working. A battery that can keep it bright for several hours will stand up to a day of roving. I’ve also used the light to test power supplies, with mixed results. It draws too much current for small ones and not enough for larger ones. For higher currents, I add some big resistors – now I’ve got hot resistors and lights all over, and sometimes the clip leads overheat, or slip off and cause more excitement. Recently I was thumbing through an electronics magazine and came across an “Ideas for Design” circuit1 for a dummy load for power supplies. Many of these ideas are questionable, but

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