Electrical Projects Low-voltage flashlight and transistor-radio batteries accumulate in the workshop and often the temptation is to discard them all rather than go through the time-consuming task of checking them with a voltmeter and then deciding which have sufficient life left to make keeping them worthwhile. Often voltmeter circuitry is inadequate to render an accurate reading. But to avoid throwing away still useful batteries, try constructing this handy go/no-go battery checker.

The battery checker has simple circuitry and inexpensive components. Test leads are connected to terminals 1 and 2 of the 4-terminal barrier strip. When the leads are touched momentarily to the terminals of the battery, the secondary winding of transformer T (a standard doorbell transformer) loads down the battery. When the leads are released, the primary winding experiences an inductive kick which travels through terminals 3 and 4 to the attached neon lamp I. If the battery is still good, the lamp will briefly flick on. Quick, inexpensive, and a lot less trouble than a VOM, wouldn't you say?

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October 12, 2008