Interference from humidifier

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  #1  
Old 02-09-06, 11:51 AM
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Question Interference from humidifier

Hi All,
This is more of an electrical question than about appliances, so I posted it here...
I have a tabletop humidifier that has a humidistat. When the proper room humidity level has been reached, the humidistat "chatters" for 5 to 10 seconds, causing ungodly interference to the TV and wireless phone. I have been unable to adjust the humidistat for a cleaner "break", so I am contemplating adding a capacitor across the switch to help lessen the arcing.

Is this a good plan? What value in microfarads would be appropriate? Yes, I could just buy a new humidifier, but this one works fine otherwise, and I don't want to add more to the landfill.
Thanks
 
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Old 02-09-06, 12:14 PM
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Originally Posted by Andrew
This is more of an electrical question than about appliances
Sounds like an appliance question.


I have a tabletop humidifier that has a humidistat. When the proper room humidity level has been reached, the humidistat "chatters" for 5 to 10 seconds, causing ungodly interference to the TV and wireless phone. I have been unable to adjust the humidistat for a cleaner "break", so I am contemplating adding a capacitor across the switch to help lessen the arcing (rapid cycling).
I believe a capacitor on an A/C circuit won't help.

(If you mean between hot and neutral rather than across the switched to the unswitched hot, again for AC, no help; but for DC it would help.)


Is this a good plan?
I don't believe so. It would surely violate the UL listing. Could you explain why you think this could help?


I don't want to add more to the landfill.
I agree with you there! How about replacing just the ailing humidistat component? Perhaps a relay?
 
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Old 02-09-06, 05:45 PM
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Originally Posted by bolide
Sounds like an appliance question.
Actually, this situation could be present in any electrical device, from a lighting contactor to a small relay, or even a thermostat, so I believe it applies as an electrical question.


I believe a capacitor on an A/C circuit won't help.

(If you mean between hot and neutral rather than across the switched to the unswitched hot, again for AC, no help; but for DC it would help.)
Nope. Capacitors are used for this purpose on AC systems all the time. I just need the correct value in microfarads.

I don't believe so. It would surely violate the UL listing. Could you explain why you think this could help?
A correctly sized capacitor will charge & discharge during each cycle of the AC power, absorbing much if not all of the energy creating the noise. I am not an electrical engineer, so I can't explain further

I agree with you there! How about replacing just the ailing humidistat component? Perhaps a relay?
I would replace the humidistat if one were available, but so far I haven't found one
 
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Old 02-09-06, 05:51 PM
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Bolide's right - a capacitor across the AC won't help with anything but RF noise redirection - not your issue. Yes, your problem is likely the humidstat switching - might be a mechanical relay (sounds like it) - might be solid state - either way, it's not working right. You can't get around it - you have to fix it, or replace it.
 
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Old 02-09-06, 07:43 PM
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inductance, capacitance, reactance

Originally Posted by Andrew
Actually, this situation could be present in any electrical device, from a lighting contactor to a small relay, or even a thermostat, so I believe it applies as an electrical question.
Perhaps as an electronics question. Your question certainly is not typical for this board.


Capacitors are used for this purpose on AC systems all the time. I just need the correct value in microfarads.
A capacitor could kill some RFI from an active circuit.
But what you have by your own description in arcing.
No capacitor of any size will stop the arcing or kill the noise it generates.

Besides, the chattering contactor is very hard on its relay and the motor.


A correctly sized capacitor will charge & discharge during each cycle of the AC power, absorbing much if not all of the energy creating the noise.
That is simply untrue. If that worked, we wouldn't have RFI to the extent that we do. Every manufacturer would simply add a correctly-sized, cheap capacitor each piece of equipment.

From where do you propose this energy is coming to create the noise?


You have a chattering contactor. The control circuit apparently is having trouble determining whether it should be open or closed. Maybe it is getting a signal feedback from somewhere, the flyback from the relay coil, the motor, or something like that. That's the problem to solve.

Adding a capacitor across the switch can't do a thing.
If half the time it stores energy, then half the time it will contribute energy.
Your net improvement is zero.

If you want to do something constructive, add a supervisory delay to it so the once the relay opens it has to remain open for at least ten minutes.
That is the essence of the problem.
 
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Old 02-10-06, 09:17 AM
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Thank you all for your answers.
 
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