Paul, I made a much smaller approx. 0.2 milliohm shunt, appropriate for installation in the controller. If it is placed in the bus that is nearest the ground potential of the controller board, the common mode voltage will be minimized. This is often the expensive part of an instrumentation amplifier. Analog Devices and Burr Brown both make appropriate devices.
The current terminals on this one are the bronze bolts and contacts from a Metro solenoid. With 1/2 inch wide strip, and the sense leads silver soldered 1 cm apart, this should work well, and maybe fit where the toroid and Hall device are now.
If we like this design, we'll need a source of bronze 5/16 x 1 1/4 capscrews.
Or just break up a bunch of old starter solenoids.
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