It is possible, but it will be difficult to get much power-handling ability this way. A TO-220 type package will be limited to around 20 Watts absolute maximum continuous dissipation regardless of how big the heatsink is. One way I've done this before is to have two power resistors: one which is the minimum resistance (call this Rmin) desired and a second which is the difference between the max resistance and the min resistance (call thisRb). I put these two resistors in series and put a transistor (FET or BJT) across resistor B. By using this transistor to shunt current around resistor Rb, to a varying degree, I could vary the effective resistance from the min to the max and the maximum power the transistor needs to handle is around one quarter of what it would need to handle if it were the only dissipating element. Another way is to use a switching regulator. Let's say your battery voltage ranges from 10 to 20V. If you made a buck converter which took 10 to 20V in and gave, say, 2 to 8V out, then you could put a fixed resistor on the output of the converter and vary the voltage setpoint to vary the power drawn from the battery. Sean On Thu, Apr 14, 2011 at 10:58 AM, V G wrote: > Hey all, instead of using a wire wound resistor for testing battery drain= , > I'm thinking of using a heat sink bound MOSFET and control the drain-sour= ce > current with the gate. I'm looking to get around a 0.5 - 2 ohm resistance > between drain and source. Is this possible? > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .