A circuit that draws a set # of mA.

Hello everyone. In my recent days of boredom (Winter sucks), I've decided to test out the capacity of certain batteries I own to test the manufacturers capacity claims. What I would like to do is construct a circuit that will draw a certain number of mA from a power source (preferably adjustable). Would anyone be able to draw such a schematic for me? Ty in advance.

any of the linear drivers we use for laser diodes will work. cheap and easy= lm317 aka DDL driver. for this purpose you only need the chip and the resistors, forget about capacitors and diodes

Anyway, how are you going to test that? once the Vin drops below 1.25V the circuit will stop and your experiment will be fucked up, IIRC special equipment is required for this purpose, since you need to fully discharge the battery. again, IIRC

A current source like the ddl circuit driving a short circuit instead of a laser diode will do okay as a test load - as long as supply voltage is over 5 volts or so (i.e. 2 cells in series to test).

You could add a led with a series resistor over the entire thing to see when it actually poops out, though you need to factor in the current drawn by the led in that case.

Most test equipment for batteries will have a timer though - probably more convenient than keeping an eye on it and recording the time manually.

Cool project! It may be disappointing though. I'm sure you'll find everyone that makes batteries is full of sht. I wonder if there's such a device as a DC kill-a-watt...

I found one! It's $60 though.

Keep in mind that you will need to define, what a "dead" battery really looks like. Will you pronounce it unusable at 0.1V? Or at 2.6V? etc..