Electronics > Projects, Designs, and Technical Stuff
Surge Protector and MOVs
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bostonman:
I've noticed electronics incorporate surge protection into their designs and I've done the same on a recent power supply.

Is it worth using surge protectors since the electronics already has them? Also, does a real difference exist between surge protector models?

TimNJ:
Not all mains powered products have built-in MOVs. It really depends on what standards the products were designed to meet, and the age of the product. Many products have them, but many others do not.

In general, I think it's worth using a surge protector if it's powering equipment you care about ($$$). I guess that goes without saying.

Yes, there are differences. Cheap surge suppressors might have only a few paralleled MOVs. After a few line surges, their clamping ability will degrade. On the other hand, a top-notch suppressor will have many more MOVs, allowing a longer life. They may also have a thermal protection circuit to keep your house from burning down. (MOVs have a nasty tendency to fail and catch fire.) They may also include line filtering components like common-mode chokes, X-caps, etc.

Tripp-Lite ISOBAR is probably the best surge suppressor on the market.
rsjsouza:

--- Quote from: TimNJ on May 01, 2019, 10:07:55 pm ---Tripp-Lite ISOBAR is probably the best surge suppressor on the market.

--- End quote ---
I haven't heard about this before. Interesting article:
https://www.tomshardware.com/picturestory/684-tripp-lite-isobar-tear-down.html
helius:
Is it worth using MOV surge suppressors when a device already has them? That depends on whether the clamp voltage is lower than the MOVs in the device. The MOV with the lowest clamp voltage will activate first and absorb the surge, while the others do nothing.

Because MOVs are sacrificial devices, the most effective and reliable surge suppression requires them to be very large, larger than would be installed in a device or even in a power strip. The first line of surge suppression should be at the distribution panel, with the lowest clamp voltage.
As a backup you can have additional, small MOVs in power strips as long as they have higher clamp voltages. As a last resort protection, the MOVs in the device should have the highest clamp voltage.

What is a reasonable clamp voltage for a 120 VAC line? You need to have a reasonable margin between normal power and the point where the MOV activates, or it will leak current, get hot, and burn out. The peak of a pure sine wave at 120 VAC is about 170 VDC, and it makes sense to leave 100% margin for noise that is superimposed on this wave (MOVs cannot filter noise). So 340 VDC clamping would be the minimum, and should be applied at the largest surge suppressor at the distribution panel. In practice, this value can be somewhat higher. The power strip MOVs should clamp higher, at perhaps 380V, and the equipment MOVs should be 400V. If they do not increase in clamp voltage as you get closer to the load, they don't serve a purpose.
coppercone2:
I use isobars because well, they are not built like shit. Its decently rugged metal construction and I am pretty sure the MOV bank is kapton wrapped.


The best surge protectors though, are the ones that power off with a contactor (meant for remote control with a relay or switch control. They have a seperate control transformer. They are meant for rack mount operation but there is no reason why you can't screw them to a plank of wood.

The best part? super spacious inside. You can put whatever kind of extra goodies for surge protection you want in one of those suckers. GDT, more movs, passives... roomy

Bad? It thunks hard when you turn it on because of the contactor. Sounds like someone hitting something with a hammer. Also, sometimes they power down when there is a brown out because the contactor slips. So it will thunk on you (unlike a mechanical switch). If you want the best of both worlds, put a power switch across the contactor, so you make the circuit with the contactor then short out the contactor with the mains switch to save the switch life. If you put it under a table it can sound a bit scary when it hits. You can also fit a arc supressor in there across the contactor to trick it out further.


Proper term: mains distribution unit (MDU)


How to make it work in the home under a table : use a saw (recommend band saw) to cut off the handles. Use a file to debur it and take it apart and drill holes in it to attach it to a plank of wood slightly bigger then the MDU to make a flange. Or make a real flange out of metal (be sure to ground it).
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