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Old 12-14-2021, 01:15 AM   #1
Pentium4
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Default Replacing MOVs in surge protectors?

I know most people would just buy a new one at the store. But hey... this is Badcaps afterall, right?

For quite some time I've had the crazy and naive notion that surge protectors just worked, and lasted forever I have been occasionally buying new units because you can't really tell how many joules are left in the MOVs after a few power surges. Some units I have had for 10 years and surely their MOVs are toast by now. Instead of buying new ones and funneling money over to china, I thought about just replacing the MOVs in the existing ones I have. All of the plugs still work and it seems like a waste to just have a bunch of "power strips" lying around.

Has anyone had any experience doing this before? Is there some "size fits all" part on Digi-Key that I can order, or do I need to match the specs of every piece in every unit I have? Appreciate any insight.
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Old 12-14-2021, 02:05 AM   #2
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Default Re: Replacing MOVs in surge protectors?

Yes they wear out but if you have clean power, they can last a while. You should match with the original as well as other parts that burn out along with the MOV when it finally took its last spike. It depends on how they designed the protection. Usually you can go bigger however, just match voltage ratings.

One thing I noticed, some of my cheap surge protectors they have the MOV but the lamp indicating the surge protection are enabled is a lie, seems to just be hooked up to an LED and a resistor straight to power.
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Old 12-14-2021, 03:47 AM   #3
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Default Re: Replacing MOVs in surge protectors?

So I just checked the two that I was suspicious about. One was made January 4, 2005 and the other was made April, 2008 and have had heavy usage. I just opened the 2005 one and I'm having a hard time deciphering all of the stats for it. It has three MOVs and they read: CNR 18D201K and have a resistor in between each.

As far as I can tell, CNR is brand or the series, 18D is the diameter, 201 is AC voltage, and K is tolerance? If so, I cannot find a suitable replacement on Digi-Key.

Here is a picture. Definitely need to do some resoldering!
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Old 12-14-2021, 05:18 AM   #4
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Default Re: Replacing MOVs in surge protectors?

those resistors probably arent.
bad mov's get hot or short out so a lot of protectors include fuses or thermal fuses
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Old 12-14-2021, 05:43 AM   #5
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Default Re: Replacing MOVs in surge protectors?

Nothing looks popped or hot here. Are you saying that they're most likely still good?
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Old 12-14-2021, 08:34 AM   #6
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Default Re: Replacing MOVs in surge protectors?

no idea - meter them.
is that capton btw or some type of glue?
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Old 12-15-2021, 12:25 PM   #7
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Default Re: Replacing MOVs in surge protectors?

I like the TMOV series from Littlefuse, they have a built in fuse so they don't burn your house down by default when they are overloaded!
And there is also a version of it with a third lead for telling if the internal fuse has gone or not, perfect to connect to a LED on a surge protector so you know if it works or not.

https://www.mouser.se/c/circuit-prot...%20rating%20ac

https://www.littelfuse.com/products/...cted/tmov.aspx
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Old 12-15-2021, 02:01 PM   #8
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Default Re: Replacing MOVs in surge protectors?

It really depends on their surge history, is what I read. MOV's age everytime they see a surge.

Long ago maybe 20 years I put Epcos S20K130 MOV's in all my power bars. None of them failed but mains is around 122VAC now, and they are rated 130VAC 1mA (170VDC) , which made me uncomfortable using them. Their operating voltage real close to mains voltage and clamping that low means they work hard. All my power bars have a metal case though.
Pulled them out and measured current at 122VAC is 0.05mA so they are still fine.
But I am changing them out to TMOV 150VAC, but these are fatter as they have a big thermal fuse on the side.

OP's strip has thermal fuses and Kapton tape, MOV's look to be CNR18D201K rated 130VAC max. operating and 200VDC 1mA (185-225V). There is coverage if they cook and burn.

edit: The APC SurgeArrest power strip recalls 15 million of them, fires, it might not be due to MOV's, but instead bad spacings between parts and pc board it arced.

https://www.electrical-forensics.com...ppressors.html guy gave 240VAC to some well duh they burned up
http://www.kerrywong.com/2018/06/10/...rge-protector/

Last edited by redwire; 12-15-2021 at 02:11 PM..
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