Would this work to confirm a solenoid valve is not burned out?

ndzied1 · Jul 18, 2014

I had a request to try to add something to a system that would check if the solenoid on a valve is burned out. I suppose one way would be to add a current sensor to the line with a discrete output and monitor that.

Another thought I had was what is in the attached image. Any thoughts on whether this would work or not? I know the coil is 22watts cold so that takes about 1.9Amps. If I put a small relay in there, will it get burned up by this much current?

kamenges · Jul 18, 2014

Unless the coil of your relay is basically resistance matched to the coil of the valve you will have issues, either one way or the other. If you want to try this type of detection you are probably better off putting a power resistor matched to the coil resistance after the valve solenoid and wire the joint between the valve and resistor into an input point.

Keith

danatomega · Jul 18, 2014

Just because the solenoid draws 1.9A doesn't mean that that circuit would also - in fact, it will be likely much less. The current would be limited to your supply voltage divided by the sum of the resistances :
24 / (R-solenoid + R-relay)

James Mcquade · Jul 18, 2014

ndzied1,

sorry, but this will not work.
you have a series circuit and thus divided the voltage between the two components. the dc current will also go down.
this is based voltage and current rules.

regards,
james

osmanmom · Jul 18, 2014

Ohm Sol + Ohm CR = Total Ohm

ndzied1 · Jul 18, 2014

Thanks guys. Current sensing switch it is

Sometimes my mechanical engineering educated brain takes over and prevents me from seeing the obvious.

diat150 · Jul 18, 2014

why dont you monitor the valve position or the output of the solenoid instead?

jrwb4gbm · Jul 18, 2014

Snip....
I had a request to try to add something to a system that would check if the solenoid on a valve is burned out. I suppose one way would be to add a current sensor to the line with a discrete output and monitor that.

Your idea highlighted in red from the original post seems like a good method.

shooter · Jul 18, 2014

1.9 Amps is very much for a solenoid (i do use them but they are proportional valves. and same for the PLC output.
you can mount a small reedcontact on top of the solenoidcoil.
or use the same contact with some wire wound around it.

Lancie1 · Jul 18, 2014

Thanks guys. Current sensing switch it is

A current sensor will tell you that the solenoid coil is using normal current, or not. It will not tell you if the solenoid can or will operate the valve when it is energized.

The only way to know that it will operate is to give it a short "ON time" and see if the valve operates. Where a valve can be switched Off/On or On/Off for a short time (and the valve has position switches), then that is the best test you could perform.

Vic · Jul 18, 2014

A relay and resistor would work

Norm

You could use a 12 volt relay with a resistor in parallel with it to sense the current. The resistor value should be chosen so that the relay and parallel resistor combination is the same resistance as the solenoid coil. You will need about a 25 watt resistor, depending on the relay coil resistance.

As others have stated, this will only confirm the solenoid coil is drawing current, not that it is functioning correctly.

Saffa · Jul 18, 2014

Vic said:
Norm

You could use a 12 volt relay with a resistor in parallel with it to sense the current. The resistor value should be chosen so that the relay and parallel resistor combination is the same resistance as the solenoid coil. You will need about a 25 watt resistor, depending on the relay coil resistance.

As others have stated, this will only confirm the solenoid coil is drawing current, not that it is functioning correctly.

This will not work. As others have Also stated above, if you add extra resistance into the circuit then the solenoid will no longer receive the full 24V across its terminals and you'll basically end up with a voltage divider with a portion of 24V across the solenoid and the rest across the resistor.

Personally, I would look at monitoring a flow switch on the actual Process that this valve is controlling. Monitoring the current just to the solenoid won't tell you if the valve fails to close, or if the solenoid itself has been separated from the valve body and is now lying on the floor!

Gil47 · Jul 18, 2014

Try clamping a reed switch to the side of the solenoid coil.
this will tell if you are producing a magnetic field,
which I feel confirms it is not burnt out

Vic · Jul 18, 2014

This will not work. As others have Also stated above, if you add extra resistance into the circuit then the solenoid will no longer receive the full 24V across its terminals and you'll basically end up with a voltage divider with a portion of 24V across the solenoid and the rest across the resistor.

If you took the time to carefully read the original post, you would have noticed that Norm was proposing using a 12 volt solenoid and a 12 volt relay with a 24 volt supply.

kamenges · Jul 18, 2014

Originally posted by Saffa:

This will not work.

Norm's original post indicates that he is driving the series combination of a 12V valve and a 12V relay with a 24V source. In that case he needs to get the voltage across the coil of the valve down to 12V anyway. An "easy" way to do this is to put a resistance in series with the valve that is equal to the valve resistance. That will split the source voltage equally across both devices, achieving the desired 12V across the coil.

You can very easily argue that this is not a good way to perform the detection function or that it is overly complicated or inefficient. But you cannot argue that it wouldn't work.

Keith

Would this work to confirm a solenoid valve is not burned out?

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