"MOVs"

[Flinx]

Hi,

Was wondering if anybody had a schematic or a project showing how to build/modify a Surge Protector using "MOV's".
MOV's are supposed to be inexpesive like 25Cents or a $1 so that you should be able make something good for cheap.

Apparently this is what's used in surge protecting power bars but the "Mov's" deteriorate after being stressed.

Any other kind of design for power filtering and surge protection?

The loving are the daring!

 

[folken]

Just get a UPS. They are getting fairly cheap now days and that would take care of your surge protection, power filtering, and more.

<A HREF="http://www.folken.net/myrig.htm" target="_new">My precious...</A>

 

[Flinx]

Inexpensive and Robust.

I could buy a cheap UPS but I was thinking of something good. And something good with filtering seems to cost $$$.
Surge protection ok ... maybe. And I wasn't thinking of batteries..I'm not running a server farm at home. I just want something to make sure the power is clean so components won't get blown away.

I was thinking that one could build something truely good and inexpensive if done properly. With MOV's you could replace etc. MOSFETs for filtering if the cost of them wouldn't be exhorbitant.. or some other technology that would or could come close.

I was hoping there was an inexpensive project. Something for $50 that would be cheaply renewable and provide some real protection and filtering.

Was hoping some electrically oriented people might know if something/project was available.


Thanks for the advice though.

The loving are the daring!

 

[jamarno]

You normally don't use MOSFETs for surge protection. Surge protection consists of devices in parallel (crowbars - MOVs, gas discharge tubes, arc gaps, transorbers, capacitors) and series (inductors - chokes) with the wiring. Chokes are normally used together with capacitors and are effective even at voltages too low to trigger the other devices. Don't build your own surge protector because the high voltage circuitry can be dangerous if made improperly. Also MOVs and transorbers should have a fuse in line in case of failure, and the capacitors must be rated for AC use, especially those connected between line and ground, where a capacitor failure combined with a ground failure can cause a shock hazard.

Most devices referred to as UPSes aren't real UPSes. A real one will continuously charge a battery and use the battery to supply power to a circuit that converts low voltage DC into 120V or 240V AC. But most normally pass the incoming 120/240VAC directly to the load and switch to battery power only during blackouts, after an interruption of about 5-15 milliseconds. This makes their surge protection inherently worse, although in practice they're equiped with very good surge protectors.

 

[Flinx]

Understand your concern about playing with high voltages and dangers.

Then is there no way one can get effective surge protection and power filtering on the cheap?

The loving are the daring!

 

[RichPLS]

I got a <A HREF="http://www.cyberpowersystems.com/1500AVR-HO.htm" target="_new"> Cyberpower 1500 </A> for $149 delivered at NewEgg.
It is the best I have ever used, cable surge, network surge, filtering and nealy an hour of battery backup protection!

<pre><font color=red>°¤o,¸¸¸,o¤°`°¤o \\// o¤°`°¤o,¸¸¸,o¤°
And the sign says "You got to have a membership card to get inside" Huh
So I got me a pen and paper And I made up my own little sign</pre><p></font color=red>

 

[jamarno]

If you know what you're doing, you can turn a cheap power strip into a surge protector by adding 3 MOVs, one across each pair of wires (left-center, right-center, right-left), and installing an EMI filter (see www.cor.com) will make it even better. Each MOV should be protected by a fuse (1 in series with the wire going to the left prongs, another with right prongs), and each MOV must be rated for enough voltage, 150Vrms for the ones going to the center prong, but in countries with 230VAC or higher voltage, the MOV connected between the left and right prongs should be rated for 300Vrms. Realize that RMS voltage is very different from clamping voltage, which is the peak-peak voltage, or almost triple the RMS voltage.

The best protection is offered by a whole house surge protector wired to the main breaker box because its earth ground connection is so much better than those of the household outlets.

 

[mozzartusm]

Send me a PM, I may be able to help you.

 

[Flinx]

Thanks for the lead "jamarro"

The loving are the daring!

 

[Flinx]

Interesting Product!!!

The loving are the daring!

 

[scalar]

So you think UPS's don't have MOVs? Hah, that is a laugh. They DO have MOVs like power strips, but usually just much larger so they can take a harder hit and still work.

Could a power strip have replaceable MOVs? Absolutely! There's not much to them... in a USA 120v strip, three MOVs connect in a triangle across the busbars. It would be a simple matter to make a power strip with a slide-in pluggable replaceable MOV module.

The main reason they don't do this is because the strips themselves are so cheap. When a power strip costs $7.99, the manufacturers likely would have to raise prices to cover the replacement module functionality. And having them built in is a way to spur you to spend another $7.99 again in a year or so. ;-)

 

[Flinx]

Thanks Scalar,

Considering the PSU has some I feel a bit better. With regard to the bars.. I wouldn't mind paying "another" $8. <b>How do I tell if the MOV's are bad and it's time to replace?</b>. Some bars are fairly expensive like $50 and that wouldn't be fun after having it for a month.

Also there are less well off people and countries who might appreciate the savings.. And those countries are also most likely the ones with power problems.

The loving are the daring!

 

[jamarno]

I don't think there's a way to tell when a MOV has gone bad unless it's visibly scorched or ruptured, but any time a fuse blows in surge protector or the indicator light goes out, all its MOVs should be replaced. Wear on a MOV is accumulative, and once the sum of the energy of each surge has equalled roughly the energy rating (joules) of the MOV, the MOV fails.