24 volt open power relay

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phillapointe

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I'm having a challenge with a 24 volt dc open power relay SPDT that controls a block heater on a generator. When the thermal switch opens it removes the dc voltage from the relay to transition it and turn the heater on, the problem is 4 volts remain and the relay will not transition. Any help will be appreciated.
 
phillapointe said:
I'm having a challenge with a 24 volt dc open power relay SPDT that controls a block heater on a generator. When the thermal switch opens it removes the dc voltage from the relay to transition it and turn the heater on, the problem is 4 volts remain and the relay will not transition. Any help will be appreciated.
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You probably need to call a technician of the genset mfgr. and have him look into it. Can't beat a man at his own trade.
 
150217-1335 EST

phillapointe:

Quite obviously there is a shunt path around the thermal sensor, or the thermal sensor does not completely open, or there is another source of current to the relay coil.

Remove the wire from the thermal sensor to the relay coil. What is the voltage from that wire to the wire that is still connected to the other side of the relay coil? Probably about 24 V or whatever the actual source voltage is. If this is the result then investagate the problem with the thermal sensor and its associated circuitry.

You might also verify that application and removal of 24 V to the relay coil causes the relay to function correctly.

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You might place some resistance in parallel to your relay coil. Sometimes the leakage voltage that holds a coil carries such a limited current an increased load will bleed it off,
 
phillapointe said:
I'm having a challenge with a 24 volt dc open power relay SPDT that controls a block heater on a generator. When the thermal switch opens it removes the dc voltage from the relay to transition it and turn the heater on, the problem is 4 volts remain and the relay will not transition. Any help will be appreciated.
Click to expand...
Can you take the wire off the relay coil and see what happens?
 
phillapointe said:
yes when I remove the wire the relay transitions, and I was wondering if some resistance in parallel would do it, will try that. thanks guys for all the help.
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It might but you shouldn't need to with a 24Vdc relay. We use an awful lot of them, mostly Omron, and have been doing so for decades and have never, to my knowledge, had to do that.
I think you have a couple of possible faults.
As was suggested earlier, the thermal switch isn't operating correctly i.e. not breaking the circuit cleanly. Can you replace it?
Or the wiring isn't just simply the thermal switch in series with the relay coil and there is a "sneak" feed from elsewhere.
 
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