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Old 15th Dec 2020, 11:25 pm   #18
McMurdo
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Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,274
Default Re: Advice on mains current sensing, safely

A little rouse I've done in the past is to wind a few turns of enamelled copper wire around a reed switch, making a very simple current-operated relay. Sometimes they use commercial versions of these to tell a shunt motor controller when the field current has disappeared, so avoiding a runaway motor.

Or make a current sense relay out of 2 bridge rectifiers wired so you get 2 4-way strings of anti-parallel diodes. Use this to shunt the coil of a 6VAC relay (RS do them). The volt drop across the diodes pulls in the relay.

Just a couple of ideas?
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