Rf relay controlling 100a contactor. Chatter over time.

BenPeirce · May 2, 2017

Hi there. I'll explain the setup first.

25mm 2 cable single phase tncs Into 3ph 100a contactor. Only switching line. Out of contactor into supply side of a consumer unit.
Coil Is controlled by separate 6a circuit with a lightwave inline Rf relay.

I've changed the contactor as upon switching on the relay chattering occurred. Seemed to do the trick, no more chatter.
However same problem is gradually ( as in over a week) becoming apparent again. Contactor is from lewden. Rf. Inline relay is from lightwave.

SparkyChick · May 2, 2017

If the coil of the contactor is driven with AC, you will get some noise, however... that 'relay'. Is it a relay proper (i.e. electromechanical) or an electronic switch (e.g. a triac)? I'm just wondering if it's say a thyristor drive and the coil is only seeing have wave AC, which would result in a lower frequency buzz I believe.

That said, what kind of frequency is the chatter? Is it resulting in contact bounce?

Curious about what this is being used for as well

BenPeirce · May 2, 2017

Hi there. Thanks for your interest. I have a client who is apparently sensitive to emf. I won't get started on they one.

Relay
LightwaveRF 500W Iinline relay, inline switching, power control, JSJSLW825 UK - https://www.directtradesupplies.co.uk/product.php/16934/lightwaverf-500w-inline-relay--white--?gclid=CjwKEAjw3KDIBRCz0KvZlJ7k4TgSJABDqOK7NCa3ufj1RvoMyXRWbs64EHozFklfK18rbllVVbSCzRoCLtLw_wcB

Noise is non existent at first however 50hz buzz can be heard at times when turning on and chatter and contact bounce occurs after weeks.

Thanks

Andy-1960 · May 2, 2017

Have you checked the ratings of the relay contacts in the Lightwave unit. They are probably rated for a resistive load and you are switching an inductive load.
Inductive ratings are significantly lower than resistive ones, for example a relay rated at 10A resistive may only be 2A inductive. A 100A contactor will have quite a hefty inrush current which has probably damaged the contacts in the lightwave unit.
I have no idea why the problem went away for a short while, but I think it would be worthwhile fitting a small interposing relay to switch the larger contactor.

PS I have just looked at the spec of the unit and the max load rating is 500w resistive... think that what I have suggested may well be your problem.