Smokin' rocket MOV

[KellyBass]

I fired up my rocket for the first time late last night and the MOV was doin some serious smokin'!...even using my light bulb gizmo. I'm not too sure about this MOV...It came out of a bin at my local antique electronics store and the bin was marked 130v-30amp. Shouldn't this be enough?

Of course, I shut everything down immediately and it was too late to pursue it further. Maybe it's just underated or marked wrong. What else could be contributing to this condition?

[passfan]

Shame on me...I don't even use one Cut it loose and rock on.

[passfan]

Shame on me...I don't even use one Cut it loose and rock on.

On second thought, how did the light react when you flipped the switch? Did it go bright and then slowly dim back down some? If not then you have a short. Check your line side wiring and if ok perhaps it's a bad device.

And I still don't use them

[KellyBass]

The bulb lit up real bright and didn't dim...until I cut off the MOV...and turned it back on! I was curious...

then the bulb lit up and dimmed like normal and everything seemed okay. All the heaters lit up and measured 6.5 and that's where I left it. Promise!

[passfan]

The bulb lit up real bright and didn't dim...until I cut off the MOV...and turned it back on! I was curious...

then the bulb lit up and dimmed like normal and everything seemed okay. All the heaters lit up and measured 6.5 and that's where I left it. Promise!

Sounds like the mov was either bad or wired wrong. We'll call it bad and from what it sounds like I would continue along with my startup procedures and aquire a replacement for later if you so choose.
Of course I always push on until something catastrophic happens and then scratch my head.

[Structo]

I seem to remember reading that the MOV component is basically ruined after a large spike.
Or perhaps it is after a series of voltage spikes.

But many computer surge protector outlet strips use those don't they?
So how do you know if the MOV or varistor is bad?

[passfan]

I seem to remember reading that the MOV component is basically ruined after a large spike.
Or perhaps it is after a series of voltage spikes.

But many computer surge protector outlet strips use those don't they?
So how do you know if the MOV or varistor is bad?

They smell after they eat a spike. I used to sell a lot of line conditioners to the guys that played the cruise ships and the receptacles on them had mov's across the line. They burned them up all the time. Something to do with the generators on the ships.

[marcoloco961]

Make sure you have the mov that has a operating voltage of 130, not a clamping voltage of 130. The clamping voltage should be up in the 170 range or higher. The MOV"s with the 130 clamping voltage only have an operating voltage of 40 - 50 volts. I made this mistake on my first build. Kept frying the MOV. Same symptoms. Light wouldn't dim with the MOV in place, but dimmed as soon as I removed it. Sounds like you grabbed one with a clamping voltage of 130.

[Structo]

Interesting.

Make note to self, working voltage of 130v clamping voltage of 170v.

[marcoloco961]

Interesting.

Make note to self, working voltage of 130v clamping voltage of 170v.

I probably ought to retract the first statement.
Here are two mouser part numbers for the MOV's

594-2381-594-51316 130 v operating 340 volts clamping


594-2381-595-54006 130 clamping 40v operating.

Quite a bit higher clamping voltage than I remembered. My mind is not what it used to be. But you get the idea. Only 40v operating on a 130v clamping MOV.

[Firestorm]

Has anybody ever tried transient voltage suppression diodes as made by Littelfuse, Microsemi and others? It looks like they are available in appropriate ratings and supposedly don't degrade with the number of surges like the MOVs do.

[KellyBass]

Make sure you have the mov that has a operating voltage of 130, not a clamping voltage of 130. The clamping voltage should be up in the 170 range or higher. The MOV"s with the 130 clamping voltage only have an operating voltage of 40 - 50 volts. I made this mistake on my first build. Kept frying the MOV. Same symptoms. Light wouldn't dim with the MOV in place, but dimmed as soon as I removed it. Sounds like you grabbed one with a clamping voltage of 130.

Aha!! It think this might be it! I grabbed the MOV during my lunch hour and didn't pay very close attention to how the bin was marked...but that makes perfect sense.

Thanks!!