SOV silicon oxide varistor

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VictorPS

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When building a simple Lightning arrestor, prefer using MOV (Metal oxide varistor) or SOV (silicon oxide varistor), or GASTube?

When MOV is failure, it is open circuit.
How about SOV? also open circuit after failure?

How do I know the MOV or SOV is still in good conditon and protecting my equipment?

Thank you,
 
I believe only a tube of some gas connecting between the two power rails will protect from a lightning strike. THe lightning ionizes the gas and makes it conductive shunting the lightning to ground rather than through the devices connected to it. I don't think it protects from other things though since a lightning strike is huge and can actually ionize the gas. Something like static or power surges can't ionize the gas (wiki also says they are much slower reacting than varistors).

VictorPS said:
When MOV is failure, it is open circuit.
How about SOV? also open circuit after failure?
Click to expand...
I believe both are open circuit normally and short-circuit during the failure (like the tube of gas). THey are both varistors after all...just made differently.

VictorPS said:
How do I know the MOV or SOV is still in good conditon and protecting my equipment?
Click to expand...
I'm pretty sure you don't...
 
Last edited:
dknguyen said:
I believe both are open circuit normally and short-circuit during the failure (like the tube of gas)
Click to expand...
the failure I mean is the component is spoilt.
As I know for MOV, it become open circuit permanently after failure , for GASTube, it is permanent short circuit after failure.
But how about SOV? Is it same like MOV?

Some good design use both, MOV is fast response (first level protection), the GASTube is a bit slow turn on, but can handle huge transient current ,(2nd level protection).

For MOV we may not know if it survice from last lightning strike.
if Gastube is fail, it will blow fuse and we know it is dead and replace it.

Also, any advantage by using SOV compare with MOV?
 
WHat I have heard is that many surge protection devices fail in such a way that you cannot tell that they have failed (like things that go in between the power rails and parallel to the load fail open, so you can't tell that they've failed).

Browse www.littelfuse.com and you will find a big PDF file describing a bunch of different protection devices.
 
I have seen a varistor that was overloaded go short circuit. It still protected the circuit because it blew the fuse that fed it, but obviously the fuse and the varistor needed replacing before the equipment worked.
 
Diver300 said:
I have seen a varistor that was overloaded go short circuit. It still protected the circuit because it blew the fuse that fed it, but obviously the fuse and the varistor needed replacing before the equipment worked.
Click to expand...
Yeah, I was confused about that. My understanding was that most semi-conductorish devices failed short, but I also heard that many surge protector devices fail open which seems to contradict itself in certain cases.
 
I would also add a fuse which will blow when the MOV does it's job, then when you replace the fuse you also replace the MOV.
 
Years ago a company made a cheap surge arrestor with a single MOV in it.
You could see the blue MOV through a window. It was labelled, "If it turns black then send it back". We used some for customers' equipment and without lightning they all turned black.

The good surge arrestors we used had gas tubes and MOVs. But the electrical authority didn't certify them in Canada because they were too "heavy" and might fall out of a worn electrical jack.

My old telephone answering machines have small gas tubes and MOVs. The protection didn't work.
 
It's really difficult for items connected to the phone line - it would cost far too much to give decent lightning protection, so they only give a fairly minimal amount.

I see a LOT of lightning damaged equipment, and for a near (or actual) strike, it doesn't matter what's in there - it's going to die!!!.
 
JUST UNPLUG YOUR DEVICE FROM FROM OUTSIDE LIGHTENING ACCEPTABLE WIRING!! hell i never trusted a surge protector, i've lost 1 TV and 1 radio (not cable) just plugged into a rather expensive MOV surge protector, it blew them up, not the MOV. Usually it doesn't take much of a voltage increase to blow newer electronics(yep they're crappy just like cars now a days, they don't know how to make anything worth a sh**) especially PCs, I've found the ONLY way to prevent that much juice from blowing something up is just disconnect and isolate all connections, unless you're on a UPS or battery backup, then disconnect it from the power source anyways. Atleast in a UPS you have some sensitive electronics to fry before it fries whatever is connected to it.
 
Any advantage by using SOV compare with MOV? Will it be better?
What is the common failure symptom for both by your experience?
 


Hehe, yeah it's starting to sound like you cannot win in the war against the lightning gods...you can only offer a sacrifice.
 
"Aw. The lightning is still very far away."
Boom!

I smell ozone. My electronic equipment is fried. I nearly got fried.
 
Like in my thread, the varistor in my light blew up (literally ), and went short circuit, blowing the fuse. So they short circuit when overloaded.
 
audioguru said:
"Aw. The lightning is still very far away."
Boom!

I smell ozone. My electronic equipment is fried. I nearly got fried.
Click to expand...

My yonger brothers house was struck a year or two ago, it blew a big hole in the roof and vaporised a few rafters!.

Everything electrical was toast! - and he had a LOT of gear!.
 
Nigel Goodwin said:
My yonger brothers house was struck a year or two ago, it blew a big hole in the roof and vaporised a few rafters!.

Everything electrical was toast! - and he had a LOT of gear!.
Click to expand...
His little surge arrestor wasn't strong enough for the job.
Thousands of amps?
 
audioguru said:
His little surge arrestor wasn't strong enough for the job.
Thousands of amps?
Click to expand...

No idea if he had one or not?, I certainly don't, I don't see them as being of any value.
 
I think a surge arrestor will light up and smoke to show you the poor job it is doing if it has a pretty close lightning strike.
 
i have a question?

WHICH is better to get 40kA RATING FOR Imax ?
A)combination of 2 PARALLEL 20 kA MOVS
B)Use single 40kA MOV
c) Multi movs consist of many small type MOVS
d) Hybrid (combination of gdt and MOV)
 
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