Electronics > Projects, Designs, and Technical Stuff
Surge Protector and MOVs
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bostonman:
I've used MOVs once, and watched a tutorial (through the company I got them from) on 'calculating' a proper MOV. If I remember correctly, it suggested three (hot to neutral, hot to Earth, and neutral to Earth), so that's what I used.

It didn't make sense to me at the time, and didn't really care if it added an extra $0.50 to the cost of my design because it was a one off. Ideally though I would like to learn the proper way to include such protection, however, as it was mentioned, modeling a surge is complicated. The power supply I designed was very simple, but I was practicing with proper design techniques without making it too complicated.

From what I just learned, I had good intensions, but it had lots of flaws. I was watching a YouTube video yesterday on spark gaps and didn't know anything about them. It went on to explain those blue capacitors, etc... Also, I need to research what X-rated and Y-rated capacitors are. hahaha  I guess lots more knowledge is needed before I design another power supply.

Kjelt:
That is pretty much how i did it,
However i put a fuse just before the mov from fase to neutral, in case the mov breaks down damage is restricted.
Then on the earth line from the two movs i put a sparkgap in series to protect for lightning.
T3sl4co1l:

--- Quote from: bostonman on May 03, 2019, 01:43:03 pm ---This being said, is using one with a common-mode choke worth it? My opinion: each additional component adds a greater risk of failure/fire. So personally I'd rather keep (in this case) a surge suppressor simple.

--- End quote ---

Right, it probably doesn't matter, at least as long as the attached equipment is FCC/CE compliant in the first place.

It could even make things worse, i.e., power line communication anything.

Inductors are a not-uncommon sight in surge suppressors because of the added impedance, particularly air-core or rod-core types (which retain reasonable inductance at high peak currents).  More of the surge is dropped harmlessly across the inductor, reducing peak current and energy dissipated by the MOV(s).  Common mode chokes may or may not be useful in this regard; I would expect normal mode (i.e., independent inductors on each line) to be most useful.  Therefore the CMC could probably be removed if filtering isn't so important.

Tim
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