Fuel-cell battery tester

Posted on May 28, 2012

This circuit was designed for testing fuel cells, but it could also be used for testing batteries under a constant current load. It provides a dynamic, constant current load, eliminating the need to manually adjust the load to maintain a constant load. For fuel cell application, the load must be able to absorb 20-40 A, and since a single cell develops only 0.5 to 1.0 V, bipolar power devices (such as a Darlington) are impractical. Therefore, this dynamic load was designed with a TMOS Power FET (Q2).

Fuel-cell battery tester
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With switch SI in position 1, emitter follower Ql and Rl establish the current level for the load. In position 2, an external voltage can be applied to control the current level. Operational amplifier Ul drives TMOS device Ql, which sets the load current seen by the fuel cell or battery. The voltage drop across R15, which is related to the load current, is then applied to U2, whose output is fed back to Ul. Thus, if the voltage across R15 would tend to change, feedback to the minus input of Ul causes that voltage (and the load current) to remain constant. Adjustment of R13 controls the volts/amp of feedback. The V0UT point is used to monitor the system.

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