MOV Question
MOV Question
(OP)
I am reading a manufacturer's spec's on an MOV. Part number is VA150L10a.
Chart says:
"Varistor voltage @ 1mA DC Test Current"
The directly under that are two columns as follows:
V-Nom Min. and V-Nom Max.
The rating under the MIN column for the MOV I am looking at is 212, and the rating for that same MOV in the MAX column is 268.
How do they arrive at those figures, what is the test procedure?
What do those figures mean?
My reason is simple. A competitor uses that MOV on all their products working on 115 VAC system. Their stuff blows up all the time, way too often with the MOVs burning out. We believe the clamp voltage is way too tight, they are catching normal common little spikes which are just too common to attempt dealing with at the MOV position, should be handled elsewhere.
Any insight would be helpful.
Chart says:
"Varistor voltage @ 1mA DC Test Current"
The directly under that are two columns as follows:
V-Nom Min. and V-Nom Max.
The rating under the MIN column for the MOV I am looking at is 212, and the rating for that same MOV in the MAX column is 268.
How do they arrive at those figures, what is the test procedure?
What do those figures mean?
My reason is simple. A competitor uses that MOV on all their products working on 115 VAC system. Their stuff blows up all the time, way too often with the MOVs burning out. We believe the clamp voltage is way too tight, they are catching normal common little spikes which are just too common to attempt dealing with at the MOV position, should be handled elsewhere.
Any insight would be helpful.
PUMPDESIGNER





RE: MOV Question
Varistors come in various different power ratings, specified for total pulse energy in Joules. You need to have some idea of the kind of transient you are trying to damp out to select the correct one. You may find that the combination of an R-C snubber circuit plus an MOV works better.
RE: MOV Question
RE: MOV Question
It's been a while since I've designed in a MOV, but I seem to remember that a MOV that is subjected to repeated spikes over time and age slowly develops a lower trip voltage as the zinc oxide grain sturcture degrades. The typicial, eventual failure mode of a MOV subjected to repeated transients is a short circuit. Early surge suppressor outlets used just a MOV. Later, in this application manufacturere began using a fuse in series with the MOV, possibly due to UL regs.
I suggest you search the literature from the different MOV manufacturers.
RE: MOV Question
Comcokid - You are correct about that GE book. D23 send me a scan of the relevent pages from that book.
Your comments were helpful.
PUMPDESIGNER
RE: MOV Question
RE: MOV Question
However there are very important differences. The impedance (slope) of the I vs V at avalanche is very large for a MOV. This is why the voltage max is so much larger that the min.
Unfortunately, each time an MOV avalances (protects) the PIV at rated current (say 1 ma) decreases. They will eventually short over time. (A small path is burned through the ZnO structure).
This is also why surge suppressors have a rated lifetime.
If you look at protection, you will see that a diode is sufficient for DC but an MOV (essentially two diodes back-to-back) is recommended for AC.
RE: MOV Question