MOV protection (not tube related)

2/22/2014 3:46:35 PMJ-F

Hi,

I have 2 power supplies protected with MOV (MDC Z151). They are all burned. Look to be difficult to find (eBay, Digikey...). The power supplies are working well. Do I have to replaced them?? Can I find a replacement?

Thank you

2/22/2014 7:25:23 PMEdd

Sir Jayyy - Efff . . . . . .

" They are all burned."

I "wunna" if those units are having the sandy type of black conformal coating which I occasionally see on some brands of units, or using the more common pale "yaller" coatings?

The uninitiated might suspicion the former black units as being "burnt".

If your power units are working, the MOV's are probably are fine, we at least know that it is not shorted.

They only come into their functional use in clipping AC line spikes coming into the power unit primary.

Or, in their worst case, REALLY coming into play if you have a HIGH voltage coming in from the AC line from a CLOSE lightning bolt hit.

I becomes apparent in their appearance then !

If you actually DO need replacements :

The universal replacement line by NTE has them being offered as their :

NTE1V150

The Mouse House . . .aka . . . Mouser Electronics . . . has them offered as

Littelfuse # V150LA1P

or their

Littelfuse # V150LA20AP version

which additionally has a shunting suppressive 1600 pf capacitance.

OR even your neighborhood Rat Shack has the more common MOV130, which tons of consumer electronics have been using for 30+ years.

Scavenging old 'puter power supplies will have them . . . . as is being seen here as one of the yellow units . . . . inside the clear temflex:

Your potential parts Sources:

The Mouse House:

http://www.mouser.com/Passive-Components/Varistors/_/N-6g7mv?P=1z0x8hp

The Rat Shack:

http://www.radioshack.com/product/index.jsp?productId=12645215

If you want to test a unit, get yourself a test voltage minimally of ~125 RMS VAC from the secondary of an isolation transformer, or old Radio - TV power transformers secondary and place the MOV in series with a 1 meg resistor and then measure across the MOV to see if it is clamping near your 150V spec.

Then move metering on over to the other side of the 1 meg to see what real peak voltage it was clamping down from.

For a REAL evaluation, use a scope to see the resultant compressed sine node tip and then an eventual slanted flat topping of the waveform under even higher test voltage.

Thasssit . . . .

73's de Edd

Ya' knows whuts ? . . . . I am a nobody . . . . . nobody is perfect . . . . therefore I am perfect ?

:Hi,
:
:I have 2 power supplies protected with MOV (MDC Z151). They are all burned. Look to be difficult to find (eBay, Digikey...). The power supplies are working well. Do I have to replaced them?? Can I find a replacement?
:
:Thank you
:

2/23/2014 11:02:45 AMRich, W3HWJ

:To replace an MOV, one would need to know its voltage rating. The post below assumes the MOV is on the incoming power line, but there are low voltage MOVs as well. MOVs come in red, black, etc. depending on manufacturer. The fact that the power supply works could mean that the MOV is open. Sometimes they crack from too much energy. An open MOV provides no protection.
NTE sells them all the way down to 12 volts.
http://www.nteinc.com/specs/10to99/pdf/movs.pdf

I do not buy NTE as they are a distributor (Re-marker) and don't make anything.

Rich

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:

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:
:
:
:
:
:
:
:
:Sir Jayyy - Efff . . . . . .
:
:
:
:" They are all burned."
:
:
:
:
:I "wunna" if those units are having the sandy type of black conformal coating which I occasionally see on some brands of units, or using the more common pale "yaller" coatings?
:
:
:The uninitiated might suspicion the former black units as being "burnt".
:
:
:If your power units are working, the MOV's are probably are fine, we at least know that it is not shorted.
:
:
:They only come into their functional use in clipping AC line spikes coming into the power unit primary.
:
:
:Or, in their worst case, REALLY coming into play if you have a HIGH voltage coming in from the AC line from a CLOSE lightning bolt hit.
:
:
:I becomes apparent in their appearance then !
:
:
:If you actually DO need replacements :
:
:
:The universal replacement line by NTE has them being offered as their :
:
:
:NTE1V150
:
:
:OR
:
:
:The Mouse House . . .aka . . . Mouser Electronics . . . has them offered as
:
:
:Littelfuse # V150LA1P
:
:
:or their
:
:
:Littelfuse # V150LA20AP version
:
:
:which additionally has a shunting suppressive 1600 pf capacitance.
:
:
:OR even your neighborhood Rat Shack has the more common MOV130, which tons of consumer electronics have been using for 30+ years.
:
:
: Scavenging old 'puter power supplies will have them . . . . as is being seen here as one of the yellow units . . . . inside the clear temflex:
:
:
:
:
:
:
:Your potential parts Sources:
:
:
:
:
:
:The Mouse House:
:
:
:http://www.mouser.com/Passive-Components/Varistors/_/N-6g7mv?P=1z0x8hp
:
:
:
:
:The Rat Shack:
:
:
:http://www.radioshack.com/product/index.jsp?productId=12645215
:
:
:
:If you want to test a unit, get yourself a test voltage minimally of ~125 RMS VAC from the secondary of an isolation transformer, or old Radio - TV power transformers secondary and place the MOV in series with a 1 meg resistor and then measure across the MOV to see if it is clamping near your 150V spec.
:
:
:Then move metering on over to the other side of the 1 meg to see what real peak voltage it was clamping down from.
:
:
:For a REAL evaluation, use a scope to see the resultant compressed sine node tip and then an eventual slanted flat topping of the waveform under even higher test voltage.
:
:
:
:
:
:
:
:
:
:
:
:
:Thasssit . . . .
:
:
:
:
:
:
:
:
:73's de Edd
:
:
:

:
:
:
:
:
:
:Ya' knows whuts ? . . . . I am a nobody . . . . . nobody is perfect . . . . therefore I am perfect ?
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:

:
:
:
::Hi,
::
::I have 2 power supplies protected with MOV (MDC Z151). They are all burned. Look to be difficult to find (eBay, Digikey...). The power supplies are working well. Do I have to replaced them?? Can I find a replacement?
::
::Thank you
::
:
: