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Author Topic: Testing MOV surge protectors Joules of energy absorption  (Read 2217 times)

Mike Sokol

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Testing MOV surge protectors Joules of energy absorption
« on: April 17, 2018, 02:01:39 pm »

I just had a manufacturer contact me about designing a test for their MOV based surge protectors. I need to build a test rig that will allow me to keep raising the voltage/joule spike I'm hitting it with until it fails or blows up or whatever. And of course I need to monitor the Joules of energy being absorbed. Sounds like my kind of gig.

I'm thinking this is very similar to how the original defibrillators worked with a pair of paddles and some big capacitors you can charge up with varying amounts of energy. Then you hit the big red button and shock the patient back to life. In this case I would keep raising the joules of energy until the circuit failed.

Anyone here have any experience with this sort of thing? I think I know how to do this in my head, but if there's a piece of gear in existence that I could hack to make it work for this application, so much the better.

I have too much fun with this, don't I? ;D
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Nathan Riddle

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #1 on: April 17, 2018, 02:35:54 pm »

Equipment in existence I don't know.

There's this thing: https://www.erico.com/part.asp?part=MGATESTER

But you could build a buckboost transformer and do the voltage calculation with capacitors. You have a very easy way to determine the current joules in the system. Run an o-scope on the leads to determine current & voltage. You can do all sorts of calculations from that :)

W= 1/2 * C * V^2
w = joules
C = capacitance
v = voltage

https://www.engineeringtoolbox.com/capacitors-energy-power-d_1389.html
« Last Edit: April 17, 2018, 02:43:03 pm by Nathan Riddle »
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Mike Sokol

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Re: Testing MOV surge protectors for Joules of energy absorption
« Reply #2 on: April 17, 2018, 02:41:26 pm »

I'm thinking one of each of these with a variable voltage charging circuit and a way to monitor the peak current/voltage. This will cost a few thousand dollars to build, but I might get a serious budget.

However, to get full power I would need a big capacitor with less voltage and more capacitance, or a big SCR with more voltage capability. I do need to get up above 2,000 Joules per spike, and even 5,000 Joules would be better. Probably need to build a scatter shield for this thing, eh?
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Mike Sokol
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Mike Sokol

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Re: Testing MOV surge protectors for Joules of energy absorption
« Reply #3 on: April 17, 2018, 02:51:32 pm »

Looks like I need one of these things designed for locomotive engine DC switching. http://www.power-thyristor.com/pulse-power-supply/

I'll have to work on my ghoulish laugh...  ::)

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Dave Garoutte

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Re: Testing MOV surge protectors for Joules of energy absorption
« Reply #4 on: April 17, 2018, 03:08:44 pm »

Looks like I need one of these things designed for locomotive engine DC switching. http://www.power-thyristor.com/pulse-power-supply/

I'll have to work on my ghoulish laugh...  ::)

We definitely need a MWah-ha-ha emoji.
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Nathan Riddle

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Re: Testing MOV surge protectors for Joules of energy absorption
« Reply #5 on: April 17, 2018, 03:13:10 pm »

I'm thinking one of each of these with a variable voltage charging circuit and a way to monitor the peak current/voltage. This will cost a few thousand dollars to build, but I might get a serious budget.

However, to get full power I would need a big capacitor with less voltage and more capacitance, or a big SCR with more voltage capability. I do need to get up above 2,000 Joules per spike, and even 5,000 Joules would be better.

Note that voltage is squared so it is non linear. To get more joules it is much better to double voltage than double capacitance.

Quote
Probably need to build a scatter shield for this thing, eh?
That's an emphatic YES!

By the way, i'm jelly about your project :) I've always wanted to build a coil gun or rail gun or something sciencey ;)
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Marc Sibilia

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Re: Testing MOV surge protectors for Joules of energy absorption
« Reply #6 on: April 17, 2018, 05:37:41 pm »

  Probably need to build a scatter shield for this thing, eh?

And be sure to make it from polycarbonate (Lexan), not acrylic (Plexiglas) which is brittle and sharp.  Almost lost a grad student I knew to that mistake in a combustion lab at school.

Marc
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Corey Scogin

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Re: Testing MOV surge protectors for Joules of energy absorption
« Reply #7 on: April 17, 2018, 05:38:45 pm »

This is very interesting. Keep us updated.

Knowing very little about how surge protectors are supposed to work, I have numerous questions:

At what point do the MOVs begin absorbing energy? At +10% of nominal voltage? +20%?
Can the energy absorption and the voltage peak be measured by separate tests? ie: Can you supply a steady 300V until the MOV is 'saturated' or are they not rated for continuous power absorption?
What is the determining criteria for when a MOV is worn out? ...when they are unable to maintain the rated voltage at the output?
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Stephen Swaffer

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #8 on: April 17, 2018, 05:54:16 pm »

Something like this?  Don't have time to calculate joules right now...

http://www.compwest.com/image/catalog/Datasheets/MegaPulse%201.2x50-8x20-12-2ohm.pdf

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Steve Swaffer

Stephen Kirby

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Re: Testing MOV surge protectors Joules of energy absorption
« Reply #9 on: April 17, 2018, 06:53:07 pm »

Something like this?  Don't have time to calculate joules right now...

http://www.compwest.com/image/catalog/Datasheets/MegaPulse%201.2x50-8x20-12-2ohm.pdf
I was thinking of all the hi-pot testers out there that can produce calibrated high voltages.  But a dedicated surge unit is exactly what the doctor ordered.

Something tells me that with the way MOVs degrage, that this would be a one shot test.  Work your way up with a fresh device each time until you start getting failures.  Then do enough around that voltage to get a statistical sampling.  Then you can decide where to rate on the curve from first failure to the mean.
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