Len,

MOV's will help protect you from *large* spikes (like spikes from
lighting hitting the grid nearby, large transformers arcing, etc.) but
will not do anything for surges, sags, or common mode problems typically
seen from poor generation. For that, you need something like a UPS, or
a ferroresonant transformer backed by MOV's for major-spike protection.

If you use a varistor with a sufficiently low clamping voltage to
protect you from surges, you'll fry it pretty quick. Varistors protect
by providing a short circuit at high voltages, and if that short lasts
very long...poof.

Using a ferro as an isolation transformer will isolate you from the
generation plant, provide transient protection, carry you through
voltage sags (depending on duration of course), and dampen surges. The
biggest downside is that they are inefficient, especially under light
loads, and that translates into heat. They are also fairly intolerant
of frequency variation.

The link below has all the info about varistors you could want:

http://www.littelfuse.com/data/Appli...tes/an9767.pdf

Keith Hughes

Len wrote:
On 14 Jan 2006 17:18:24 -0800, "w_tom" wrote:


Len wrote:

But what do you think of the varistor/fuse setup? I also want to use
it in the incoming shore connection. Some shore connections are
generator powered. That means there is a risk of the null hanging a
bit loose what may cause v-spikes also. Would this setup protect my
combined inverter charger in your opinion?

Destructive transients are done in microseconds. Fuses take tens or
hundreds of milliseconds just to consider tripping. Varistor life
expectancy is defined by a parameter called joules. And then you must
define the type of transient - longitudinal or transverse. The most
damning part of your theory is no numbers. With numbers, you have far
more to consider. Properly noted is that electronics already have
internal protection. So your only question means you must first define
how bad that generator really is. Again, get numbers - specifications.
Without first defining what you are protecting from, then no one can
provide anything but wild speculation - Rush Limbaugh type response.


Wow, of course, thats it, get numbers and specs.... Why didn't I think
of that????