how to use relays to limit current?(i.e the circuit opens if current exceeds a certain value)?

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  • 9 years ago
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    It depends on the voltages and currents involved, and on the drop in voltage that can be tolerated.

    For example, if you have a 100 volts DC supply, a relay in series with a coil rating of 3 volt 50 mA will close if the current exceeds 50 mA, and you can use a NC contact set to get a circuit that opens on excess current. Shunt resistors will change the sensitivity of the relay.

    You will have a 3 volt drop in the output at the point that the relay trips. And you will need to use a contact to latch the relay closed if you use the contacts to turn off the supply.

    Other methods involve transistors and opamps and relays.

    Or transformers and relays for AC current.

    .

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  • Anonymous
    9 years ago

    You must select a suitable circuit breaker to connect in series with the relay. A circuit breaker may be rated at 6 amp for example but requires a certain length of time to operate. The higher the current then the quicker it will operate. You could use a fuse but would need to keep on replacing it whereas a breaker would only need to be reset. Even a breaker has a limited number of operations before it to would need replacing but may be several thousand operations. Check that the voltage is compatible with your circuit. If the circuit is fed from a higher voltage you could insert the breaker there.

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