Testing a contactor coil

[Dave0098]

ive been working on a contactor at work, found the old 1 had welded it self together, giving an incorrect signal to the running lamp back in the control room as the auxilary contactors werent disengaging completly.ive since changed the contactor and i think ive installed a duff contactor unit as the coil wont pull in the contactor, i wont to check the coil to make sure its nackerd, im just wandering what sort of resistance i should get across the coil which would indicate either a bad or good value. ive double checked all my connection and they are all good and correct, you can actually here the contactor trying to pull in but it just wont which makes me think the coil is duff.

the contactor is 3 phase, 415v, 110Amp. and the coil is 110v,

thanks for any help.

cheers Dave

 

[carnanee4]

Dave
The first step would be to establish that the replacement coil is indeed 110V, I assume that it is AC fed and therefore you are likely to just be able to verify continuity with an ohmmeter, The measured resistance could well be in the order of a few ohms which tells you very little as it is the impedance that determines the coil current. You could measure the applied voltage in situ and see that it is 110 or perhaps you could remove the contactor to the bench, feed it with a proven 110V and check that it can pull in.Some times the coil laminations can come adrift and impede closure

 

[Dave0098]

the coil is deffinetly 110v, i know that normally you take a feed off 1 of the phases to power the coil through the control circuit, but this coil is deffinetly fed from 110vsupply.

testing insitu is not really possible as the contactor is hard up against the cubicle side which doesnt really allow for test probes.

i might give it ago on the bench and see if it is working that way.

cheers Dave