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High DC Current Indicator
designed by David A. Johnson, P.E.

A while back, someone requested a simple method to indicate when 20 to 50 Amps of DC current was flowing through a wire. The circuit below works well and is about as simple as you can get. A sensitive reed relay from www.Jameco.com acts as the current sensor.
The magnetic field produced by such a current is enough to close the relay contacts, if one or two turns are wound around the relay. The turns do not have to be tight. I was able to close the contacts with two turns about 2 inches in diameter with 20 Amps. A simple LED and resistor can be used to indicate the current by tapping into the automotive +12v supply.
Circuit Circuit High DC Current Indicator designed by David Johnson

 

 

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