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Discussion Starter · #1 ·
We installed some fans for a customer with a speed control for them, all worked fine. The customer then asked for them to be put on a timer so they could be set to run for a few hours and then shut off. We installed a 30A clapper relay before the speed controllers that was controlled by a simple timer. All works well till you slow the fans down to about 1/3 speed and then the relay starts to chatter. What would make the relay chatter when it is before the speed controls? Has anyone else seen this and if so what was the fix?

The fans are 220V and pull about 8A per. There are 2 on each circuit and have their own speed control and relay. The timer controls just the relay coil and is on a different circuit than the fans. Voltage to the coil is 120VAC and when chattering it is still 120VAC that is coming to the coil.
 

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Do you know the technical jargon for "clapper" relay? I've never heard that term before.


Sent from my iPhone using Tapatalk
 

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Discussion Starter · #9 ·
Welcome aboard @unitedgreg!

One question, what was the reasoning in this choice of relay over a standard contactor?
Relay or contractor, it is still the same concept of a coil that pulls in some type of mechanical contact to close the circuit (or am I missing something there). I am guessing that a contractor will do the same thing, as I am assuming that it is some type of harmonic issue that is causing this problem when the speed control is turned down.
 

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Old Grumpy Bastard
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Relay or contractor, it is still the same concept of a coil that pulls in some type of mechanical contact to close the circuit (or am I missing something there). I am guessing that a contractor will do the same thing, as I am assuming that it is some type of harmonic issue that is causing this problem when the speed control is turned down.
I was just curious as to why and thinking the current required to pull in the contacts may factor into the problem.

If the relays are taking out the power to the speed controls I fail to see how it could be a harmonics issue even if it does sounds like a logical conclusion.
 

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Discussion Starter · #11 ·
I was just curious as to why and thinking the current required to pull in the contacts may factor into the problem.

If the relays are taking out the power to the speed controls I fail to see how it could be a harmonics issue even if it does sounds like a logical conclusion.
My first thought it was on the load side of the speed controller and it was a harmonics thing but they assure me that it is on the line side which makes no sense to me at all why it would only do it when the speed controller is turned down. I am told that it does it more or less depending on how far down the speed knob is turned. :001_unsure:
 

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Old Grumpy Bastard
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My first thought it was on the load side of the speed controller and it was a harmonics thing but they assure me that it is on the line side which makes no sense to me at all why it would only do it when the speed controller is turned down. I am told that it does it more or less depending on how far down the speed knob is turned. :001_unsure:
One would really need to see a diagram of exactly how the wiring is done to draw any real conclusions.

I get the feeling only one side of the 220v is getting broken.
 
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I can not quite connect the dots but i wonder if the speed control is using PWM it may backfeed and somehow open that clapper.
 

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From what my guys told me, they have the relay on the line side and before the speed controllers.
My first thought it was on the load side of the speed controller and it was a harmonics thing but they assure me that it is on the line side which makes no sense to me at all why it would only do it when the speed controller is turned down. I am told that it does it more or less depending on how far down the speed knob is turned. :001_unsure:
Ok so, you're not even there, and going by what you are told by someone else, and you're trying to diagnose this over the internet.

Go to the job, draw what you have, take pictures, include part#s, show us, and I bet we solve your problem.
 

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Box of donuts says the speed controller is in the control circuit.

Make sure your measuring voltage with a good RMS meter and also check frequency.

I suppose it's possible that there are enough harmonics that it's screwing up a truly independent control circuit, but that's a long shot.

If you determine it truly is independent, put a 60W lightbulb in parallel with the coil temporarily and see if that attenuates the chattering.
 

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Still haven't seen the diagram, but the timer and the "clapper" wiring both just need to be in the control circuit. No contacts of these should be needed in the power wiring out to the motors.

This is just from envisioning it in my head and I've had a few cocktails tonight (Ok, ok, not really cocktails, just whisky on the rocks).
 
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