Need help with Relay chatter

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drjak

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I have this project consisting of a current sensing relay energizing a motor control relay. The motor is a squirrel cage fan that has a small 120 v AC motor with approx. 2 amp draw. I have two devices that I need to sense a current draw on with the current sensing relay which will then energize the motor control relay. Either one of the devices needs to independently energize the motor control relay. I used a rather simple and inexpensive current sensing relay, that has a contacts rating of 50 ma. which is adequate to control the 120 V AC coil of the motor relay. The current sensing relay is designed to have at least 4 amps of AC current flowing in the wire passing through the sensing portion of the device to close its contacts. It states in the instructions, if you need to activate the relay on a lower current, you can loop the wire a few turns through the sensing portion to achieve this. Of the two 120V AC devices that I need to sense current draw on, one of them has a 70 ma. draw and the other has 1.3 amps draw. In order to sense these lower currents which are less than the 4 amps, I had to loop the wire a few times to get the 70 ma draw device to energize the motor control relay and as a result the increased sensitivity is such that external 120V AC line spikes can cause the motor relay to chatter. (false trigger) This false triggering usually occurs when other larger motors on the same 120V AC line are powered on or off. In my searching for an alternate current sensing relay with higher contacts rating, which I could then control the motor directly and a time delay circuit built in, which could be used to minimize the spikes issue, the best I have found so far has a trigger current range of 100 ma. to 1000 ma. The down side of this type of current sensing relay is they are expensive and the 70 ma device would not trigger it.
I would appreciate any suggestions with a way to stop the false triggering. Thank you.

Ken
 

Looks as though the current sensing relay is picking up glitches straight from its power lines. Have you tried to feed its power via a mains filter? The other bit of it, the magnetic circuit which is meant for your current conductor is very sensitive, perhaps its picking up the magnetic field from one of the other relays?
Frank
 

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