Wednesday, March 20, 2013

Low Cost Current Clamps for Whole House Power Monitor

I was looking for two current clamps to measure the currents through the main breaker for my house.  It's a 200A service, and the conductors are about 5/8" or 16mm.  The ones I found at Sparkfun and Seedstuidio are too small to fit around my wires.  Larger ones that I found were either closed core or expensive.

Finally, I found these very nice, low-cost current clamps from Steren Shop.  They just came yesterday and I won't have time to really test them out till the weekend.  But I just had to open them up and see what I got, for only $11.29 each.  I have to say, they look pretty decent!

That's a 6" ruler on the right.  The jaws are plenty big enough to go around my wires. I took the back off one of them, and as I hoped, I can reduce the overall size of these by removing some (or all) of the black housing, if needed to fit them inside my breaker box.

The circuit board has two "burden" resistors, selected by the range switch.  There's also a trim pot for calibration.  I'll probably come up with my own value for the load resistor, and do the calibration in the Arduino sketch.  So I might remove the circuit board and switch and use just the yellow jaws and my own resistor.  The spring for the jaws is part of the black plastic housing, so I'd need something else to keep them closed.

In any case, this will be an AC voltage signal, so I'll need some signal processing before the Arduino analog inputs.  I may copy part of the Kill-A-Watt opamp circuit.

As a bonus, these came in a nice zip up case, so if you want to use these as they were designed, to plug into a DVM, there you go. 

These are made in China, and the US distributor is Steren Shop.  The model number on the front says Steren 603-285.  They are CE marked, and rated for 600V, and 400A max.