Self-powered Fast Battery-Tester

Posted on Feb 5, 2014

This circuit runs a fast battery test without the need of power supply or expensive moving-coil voltmeters. It has two ranges: when SW1 is set as shown in the circuit diagram, the device can test 3V to 15V batteries. When SW1 is switched to the other position, only 1. 5V cells can be tested. * Switch SW1 in the position opposite to that shown in th

Self-powered Fast Battery-Tester
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e circuit diagram. * Place the battery under test in a suitable holder or clip it to the circuit. * Wait some seconds in order to let C8 reach its full charge. * LED D1 illuminates very weakly only in presence of a new battery, otherwise is off. * Press P1 and keep an eye to LED D7. If D7 remains fully off the battery can be in very good state. * If D7 illuminates brightly for a few seconds, the battery is weak. * If D7 illuminates weakly for a few seconds, the battery is still good but is not new. * If you are suspecting a 1. 5V cell to be completely discharged, a better test can be made wiring two 1. 5V batteries in series, then running the 3V test. FET Q1 provides a constant current generator biasing LED D1 and Q2 Base. In this manner D1 illuminates at a constant intensity, independent of battery voltage from 3 to 15V and Q2 (when P1 is closed) applies a constant current load of about 120mA to the battery. IC1 is a square wave generator oscillating at about 3KHz. IC2 acts as an inverter and drives, together with IC1 but in anti-phase, Diodes D2-D6 and Capacitors C4-C7, obtaining a voltage multiplication. C8 is charged by this raised voltage and R8-R10 form a voltage divider biasing the Base of Q3. When P1 is open, a very light load is applied to the battery under test and Q3 Base is biased in order to maintain LED D7 in the off state. Closing P1, a 120mA load is applied to the battery under test. If the battery is not...

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