Electronic – Best shunt resistor for power meter application


Looking for a shunt resistor for measuring power usage and was wondering if anyone had any experience with these.

It should be capable of handling 110V/20A in-home circuit.

EDIT: Energy monitors are the rage these days and I was thinking about putting a simple circuit together to try out. This would be used to measure a typical appliance or electronic device such as stereo or television. Similar to a Kill-a-watt or multimeter. I haven't really thought about accuracy as much as getting something to work well. I haven't thought this all the way through just thought maybe some here may have already "been there done that".

Best Answer

The key is finding one with low enough resistance that it doesn't have to dissipate much power.

Two of these in parallel would do the job: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=TMC5-.10-ND

With two in parallel, the resistance will be 0.05 ohms, so at 20 A, you'll have to dissipate 20 * 20 * 0.05 = 20 W. They're rated for 5 W continuous, or 10 W for the two of them. As long as you don't have to maintain 20 A, they'd work fine.

I'll see if I can dig up something better.


Edit: here's a better solution.

Try one of these: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MR50.01FTR-ND

The resistance is 0.01 ohms, so at 20 A, you'll dissipate 20 * 20 * 0.01 = 4 W. The part is rated for 5 W continuous, so you're safe.