MOVs and surge protection/transient absorption

[WBear2GCR]

Thought I'd mention that I've read that MOVs will not provide protection after an initial "hit"! Apparently they change characteristics once they are "hit", moving the threshold voltage substantially or making them not work properly at all.

The information I've read says that in practice a large inductor and suitable shunt capacitors will provide superior performance compared to a MOV - it's just that the inductor is way bigger, so it is not a popular method.

For whole shack protection, it seems to me that the inductor method is a pretty good idea...

Seems to me that it is possible that a large iso transformer would likely be sufficient,  due to the large self inductance, although I'm not certain of that. The resources I've read have indicated series inductors on both sides of the line work better than 99% of all other transient suppresion devices and methods.

So, FYI, don't count on those MOVs to provide long term protection, since once they take a good "hit" apparently they go south - and there is no external indication that the performance has been degraded.

           _-_-WBear2GCR

[WA1GFZ]

I have a box full of dead Cubic R3030 power supplies and a number of them have failed due to MOVs. When one of them fails the bridge rectifiier gets fried and sometimes takes out the circuit board.

[K1DEU]

I do not suggest using a MOV for Power Transformer protection. 

With the Transorb and MOV in parallel the slow MOV only keeps the transorb from shorting in a good blow. Therefore we do not have to unsolder the transorb that shorted in a picosecond or faster and saved the transformer magnet wire!

Yes we do have to reset the circuit breaker or change the fuse towards the Mains.

These two devices in parallel have been proven many times!

Reference my recent post  http://amfone.net/Amforum/index.php?topic=12685.msg98426#msg98426

John K1DEU

[WBear2GCR]

yeah John, but my point is that after even one hit the MOV is basically useless and there is no way to tell if it still is working without removing and testing its parameters. That's the problem with them... it's unclear to me if the MOV ever gets to do anything if the Transorb fires first? Since both are voltage threshold devices, if the Transorb fires, it pulls the voltage down before the MOV gets to "see" sufficient voltage to fire. Which does make the MOV a sort of back-up I guess. 

And, if it for your shack, then the inductor solution on the mains obviates all that stuff...

            _-_-bear

[WQ9E]

There is some useful information on ICE's webpage:  http://www.iceradioproducts.com/10.html

By the way, since installing ICE suppression devices at the service entrances for my house, barn, and garages I have had no damage to anything in over 10 years.  Prior to that I had several "incidents" in my rural and lightning prone location and lost on separate occasions a well pump, several security lights, phones and computers.  The only negative issue is a bit more flickering during thunderstorms and you can also hear the suppressor box humming a bit from the high pressure sodium lights and also when the backup generator is in operation, probably the noise is from the inductor in the RFI network.

Rodger WQ9E

[WBear2GCR]

Sorry, but I don't think their method of gas discharge tube and MOV is really going to do the job. Re: Their number #30A...

This is a better idea: patent #7184252
It is a commercial product from a company called ZeroSurge.

Very clever, imho.

You can use any one of the free patent to pdf download sites to read it...
He has a number of patents, I think this one describes the basic idea.
Make sure you get as far as figure 4.

His site shows some graphs of performance as well...

Not sure if there are any other methods that work as well or better than this one.

                 _-_-bear

[k4kyv]

MOV's still let a lot of overvoltage through.  I seem to recall that a surge protector for 110 volts allows something like 600 volts maximum slip through before it self-sacrifices.  I don't consider that to be much protection, anyway. I think an isolation transformer would do just as well, since the core would saturate and limit the amplitude of the surge in the secondary winding beyond some point.  From my experience trying to use available transformers when I didn't have a correct one, once you get past about 150% rated voltage, the transformer begins to show signs of core saturation, with additional voltage causing the primary to grunt and draw excessive current without a corresponding increase in secondary voltage.  So I would assume a large peak would be clipped by core saturation, and hope that the transformer would self-destruct prior to the equipment connected to it.

The best surge protection is to completely disconnect everything when there is a theat of thunderstorm activity.  The lightning storm map and internet WX sites are a big help these days.

[K1DEU]

Randall; The transorb doesn't allow the MOV to be damaged    and   if  it did allow the transorb to be damaged all that would happen with a good hit is that the bi-lateral transorb would be shorted     still with no equipment damage.  My Universe engineered method has been copied many times over around the planet. Please 0bserve the component values for 220 and 440 VAC.  This is not speculation  73  John

[WBear2GCR]

John, then what is the purpose of the MOV?

For the MOV to fire it has to receive an overvoltage of sufficient level (that level depending on the particular MOV's specs), so if the Transorb kills the voltage spike, what does the MOV have to do??

Clearly, if the Transorb shorts, then other than blowing up or blowing a fuse there is no chance for an overvoltage... 

        signed,

             confused

PS. anyone look at the patent?

[WA1GFZ]

isolation transformer works great. High voltage the thing just saturates. Good cmmrr
i don't think you can use MOVs in aircraft equipment.

[W3SLK]

Why not use something like a Sola power conditioner and CVT and be done with it?

[N3DRB The Derb]

http://members.cox.net/pc-usa/station/ground0.htm

I like what this guy has to say on the subject. I'm following his advice on setting up the new station.

Let's say a nearby strike imposes 4000v on the utility pole wires (above or below ground) heading toward your house wiring. At your AC service panel, ground is bonded to neutral (this is code). Most Common-Mode  (Line-to-Ground and Neutral-to-Ground) transient voltage stops right there by virtue of this bond. You could put a powerful MOV arrestor there, before the electric panel. Your electric utility may sell these, or you can have them installed (with utility permission).
 As few homes go this expensive route,  we will assume that 4,000v wave is still riding on the hot wire (Line), with the differential being to neutral, as it always will be inside your home. Non-degrading silicone avalanching diodes *  in "normal-mode" suppressors will reference this over-voltage back to the neutral line in < 5 nanoseconds.  You will see later that at the radio station, referencing surges only to back to neutral makes all the difference in the world! This normal mode transient voltage suppression protects against not only lightning, but against all surges that typically happen in the house or station. Standard MOV power-strips are dangerous here, taking between 5 and 20 microseconds to begin to act, and then shunting surges very few times before they can short and burn.  Also, you will get a lesson in why bonding is important the first time your MOV-power-strip shunts 4,000v across an unbonded piece of "AC grounded" equipment. It can also be incredibly destructive when it short circuits high ground potential up into your house wiring from your own ground system!

MOV-type "surge" power strips are deficient and we were all misled by big names in the industry for decades.  MOV's are dirt cheap (pennies) to make and that's one reason they are so popular. They are not safe indoors! They may self-ignite when the MOV's eventually fail-shorted. Never use these in a home that employs lightning protection for communications equipment. It is possible to design a total system that uses only MOV type suppressors and this should be done by professionals only.  Never mix normal and common-mode surge suppression on the same branch circuit.

[WA1GFZ]

CVT will work but it makes a lot of distortion on the output and needs a good filter to get it back to a sine wave if it is an issue. Not a good idea to hang a switcher power supply off a CVT.

[W3SLK]

Frank said:

CVT will work but it makes a lot of distortion on the output and needs a good filter to get it back to a sine wave if it is an issue. Not a good idea to hang a switcher power supply off a CVT.

That's why I said about a 'power conditioner'. I just took one of these to the Vortex and it is making me think about it. Not only does it have the CVT but the smoothing caps/filter required to make clean AC.

[WA1GFZ]

That should work great. Usually a CVT has kind of a square wave output and inductive source.

[Steve - WB3HUZ]

Motor-generator.

[k4kyv]

Motor-generator.

...with the motor and generator at least 2 feet apart, coupled together with insulated shaft.  Internet connection via fibre optic cable.

[KB2WIG]

Ya really need the motor driving a flywheel to do it rite...............  klc

[nq5t]

John, then what is the purpose of the MOV?

Start a fire. 

I've become leary of the things in general after one of several high quality name-brand surge protectors I once used on my computer systems, ham radio gear and other things came close to burning the house down.  It's just a good thing I was home and smelled the smoke and could hear the sizzle.  At least it was in a mostly metal case and not plastic ....

Grant/NQ5T

[w3jn]

When I was posted overseas we had a brilliant idiot recommend that all computers be protected with surge protectors.  The city power being 220V, the computers were all connected to step down autotransformers.  The MOVs in the surge protector were connected each leg to ground and designed for 120V.  If you consider the connections in an autotransformer layout you could very well end up with 220V to ground on one leg of the power.  So MOVs were blowing at random and starting fires here and there.  We ended up throwing out all of those expensive surge protectors but never lost a computer to so-called "surges", even with the third-world power.

Those things are a complete waste of money and time, and are dangerous IMHO.  Never use 'em on any of my computers at work or home, and have never lost a PS in one either.

[k4kyv]

Granted, an isolation transformer may offer some protection against surges, but what about the pole transformer feeding your house?  Isn't it basically a step-down isolation transformer?  If a huge lightning surge comes down the 7.2 or 11 KV line, the pole pig should saturate and limit the voltage induced onto the 120-0-120 v secondary.  The pole transformer may be designed to handle many more KVA's than you normally draw off the mains, but voltage spikes should still drive the core to saturation and limit the secondary voltage.

I can't believe that the high amplitude surges that sometimes occur during lightning  storms are induced only from the drop line between pole transformer and utility entrance. 

But then, the destructive spikes may be common-mode, coupled from the HV line via the capacitance between transformer windings, and the neutral side of the primary and secondary lines, which are all tied together and grounded to the case of the pole transformer.  Lightning surges are of such short duration that they act more like RF than 60~ or DC.  Just like getting RF out of your shack, surge elimination may appear to violate all mortal logic.  Even the heavy ground wire coming directly down the utility pole may offer little or no protection, just as a heavy conductor running from an upstairs transmitter to a ground rod/radial system may be hot as a firecracker with rf at the transmitter end.

Imagine what will happen if BPL is universally deployed and the power company bypasses every pole transformer for all frequencies between 1.7 and 80 mHz.  That means the transformer will also be bypassed for lightning surges, and the customer will lose what protection the transformer did offer.

[Bacon, WA3WDR]

I know that the Joselyn gas-gap surge protectors for telephone control lines that I think GE used back in the 80s helped solid-state phone line equipment survive lightning strikes.  As for power lines, I have used MOVs with apparent success, or at least no fires, but a situation of autotransformers and unknown line-to-ground voltages is not really kosher.  I remember in the 70s having rectifier failure in TV cameras at a nuclear generating plant, where the camera was under the 300KV lines and you would thow a 1" spark when you touched anything in the cherry-picker while accessing it.  Those cameras did not have any MOV or other line protection, and in retrospect I am sure that is how the diodes failed.

I think that there should be fuse protection such that a conducting MOV will blow a fuse rather than cause a fire.  This would have to involve fusing both sides of the line to protect in a non-standard autotransformer arrangement situation.  And it could result in a fuse failure in a surge condition that did not kill the MOV.

[Steve - WB3HUZ]

I can't believe that the high amplitude surges that sometimes occur during lightning  storms are induced only from the drop line between pole transformer and utility entrance.

Probably not Don. More likely differential "grounds."

[w5kcm]

Years ago my Ham Shack burned up due to the MOV. 
Be very careful using anything with the MOV. I learned that many times they fail with spewing holt molten metal. My fire came from one of those little cube surge protectors that had a MOV inside.
Randy