Using a Varistor to protect ceiling fan electronics

Old 04-24-11, 07:13 AM
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Using a Varistor to protect ceiling fan electronics

I have a Casablanca ceiling fan with Intelli-Touch that I'm installing and I saw an application note from Casablanca recommending the installation of a Metal Oxide Varistor across the AC line to protect the electronics from high voltage spikes. I'm wondering if this is really needed and if anyone knows of specific MOVs to use for this? Casablanca has their own part number for this, but I'd like to know the generic part number. Thanks.
Larrylee13 voted this post useful.
Old 04-24-11, 11:13 AM
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Sounds like Casablanca is being sneaky, shifting the liability to the home owner instead of them. It has been a long time, but as I remember a simple MOV is the bottom of the line for protection. There are better ways, but more expensive. Somebody can correct me if I'm wrong, but the method of protection for a MOV is to short out high voltage spikes. Over time they degrade and eventually just short out. If not placed where they can take out a fuse they become a fire hazard. Low risk of that happening, but obviously, enough so this manufacturer doesn't want to install one.

Installing one you select instead of the one they recommend makes you more responsible. If they say to use one and you install the one they sell, then hopefully they will not have an issue.

It is pretty much your call as to does your area experience a lot of spikes. It used to be the old magnetic ballasts on florescent lights would generate 10,000 volt spikes at times. Today, especially with the electronic ballasts, I don't thing the problem is that severe. However, even the electronic ballasts get knocked out from time to time.

If you choose to add one, I recommend you use the one they suggest.

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Old 06-09-14, 02:20 PM
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MOV usage in home circuits

I just saw this thread in searching for info for my ceiling fan application. I sometimes hear a little "clunk" when switching the fan off from the wall (cheap) switch. This is probably due to interrupting the voltage when the fan current is max, leading to an inductive "kick". One way of limiting the generated back emf is to use an MOV, but there are considerations as indicated in this thread. I am including an link to an application note explaining the issues. The major issue is if the device is subjected to abnormally high voltage, high energy spikes and the neutral is opened to the load. I have attached the link.

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Old 06-09-14, 04:15 PM
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Sort of an old thread but I wanted to clear the air and add some important information to this thread.

When you turn the fan off you are probably hearing a relay release.

In that Littlefuse release they were not talking about the neutral to the device, like the fan, being lost...... they were talking about a loss of neutral as in a multiwire branch circuit or a loss of neutral at the panel. That type of loss of neutral would result in upwards of 240vac across 120vac circuits. Any time you have that loss of neutral anything connected to the circuit is at risk for meltdown.

That aside.... my opinion is that surge suppression should be built into a device, like that fan, which carries a UL rating..... not added to it.

If you are set on adding an additional varistor in the circuit with your appliance/device then a fuse must be installed before the MOV to eliminate it's self destruction and the possibility of fire.

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