Solenoid coil operates normal for first few seconds. Then current drawn increase and voltage drop. Root cause?

Question

Solenoid coil was used in a refrigeration circuit and is exposed to marine environment. Current fuse eventually burnt, causing circuit to shut down. I have the solenoid coils in my possession to do a teardown analysis. Need advice on how to determine the root cause of failure and concrete evidence.

My solenoid is 24 VAC rated. I have a power transformer which converts 460 V to around 24 V. Power frequency is 50 or 60 Hz. I need to be very cautious with the teardown as every evidence is crucial to finding the root cause.

Answer 1

Usually... with selenoid coils..... There is a circuit that fires/activates the coil which gives full power to the coil for the fist second or two so it pulls the core in solidly. Then the circuit switches over to the holding current which if by far lower and will keep the core in easily. The holding current alone will not cause the iron core to be pulled in - it is too weak..... the raw DC power with the current limiting circuit bypassed will do it easily.

I suggest you check the diagram if you have one or trace the wire(s) if they go to another timed smaller relay or solid state delay "relay" which cuts the current for/in the holding mode. As I said - if that circuit fails and the selenoid gets the full current all the time, it will overheat rapidly and shorts out the windings.

If the coil overheated too much and the windings are shorted due to the laquer insulation of the transformer wire having burnt off - you then have to rewind the coil or get a new selenoid. Hate to tell you this - but I have gone through that scenario a few times.

Answer 2

Sounds as if the salt air has worked its way into the coil and caused a 'partial' short between the windings. When you tear it down, look for places that have been obviously hot.

Doug

Answer 3

Look like you go a leak current somewhere.
This will coz a short circuit when it heat up.
If you use a meter to measure all will look OK, but when you power up it will drain a very high current.
Try to use a Mega meter to measure it.

Answer 4

you may be able to up grade the system. check with the company in the repair section there might be an up date on what their techs should do when they encounter such an isue.

Answer 5

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