Varistor to shield voltage spikes
 

Len wrote in
:

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



The more important number, in the middle of all this extensive research, is
"How many of this model welding machine was destroyed by power line
conditions in the past 5 years."

I bet the number is damned near zero making all this thread moot.

Varistor to shield voltage spikes
 

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????

Varistor to shield voltage spikes
 

Thanks Ken, useful info.
Your remark about the isolation transformer (which I have installed)
as well as your url.

Regards, Len.


On Sun, 15 Jan 2006 09:24:30 -0700, Keith Hughes
wrote:

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

Varistor to shield voltage spikes
 

On Sun, 15 Jan 2006 10:32:47 -0500, Larry wrote:

Len wrote in
:

I did. But I guess these pimplefaced youngsters that call themselves
full blown sales-people don't know anything usefull and therefor tend
to avoid any just ANY risk of being accountable.



It's called creating an "implied warranty of suitability for a particular
purpose".....
{...snip.......)
....The manufacturers have a buzzword to explain it all away.
\They call it "buyer's remorse", placing all the blame on the buyers.

My attorney disagreed....(c;

You said it all Larry... :-)

The thing that irritates me most about a vaste majority of these so
called "sales people" is their fatal combination of 1) an enormous
lack of product-knowledge and reasonable client-orientation and
2) this inexplicable attitude consisting of selfindulgment and some
utterly misplaced feeling of superiority. In other words:
Arrogant Ignorance summa cum laude...
When I've got the time I like to play around with them sarcastically
just to see their pimpled faces become pale...

Regards, Len.

Varistor to shield voltage spikes
 

Cut through and identify useless sales people quickly. First demand
spec numbers. Every so often, one will provide those numbers. He is
the only one to talk to. A sales person who cannot provide numerical
specs up front is useless for any answers.

What is the THD of that generator or a UPS in battery backup? If he
doesn't know, then he will never provide useful numbers for protecting
that arc welder. THD is only one important criteria. But demanding
that number alone will weed out so many - most all - useless salesmen.

Biggest concern about a generator is not transients. Some generators
do not recover well from load changes. But then electronics inside an
arc welder should make such voltage variations irrelevant. Neither
transient suppressors nor a ferroreasonant transformer will solve that
problem since one is for voltages much higher and the other is for
voltage variations much smaller.

Len wrote:
The thing that irritates me most about a vaste majority of these so
called "sales people" is their fatal combination of 1) an enormous
lack of product-knowledge and reasonable client-orientation and
2) this inexplicable attitude consisting of selfindulgment and some
utterly misplaced feeling of superiority. In other words:
Arrogant Ignorance summa cum laude...
When I've got the time I like to play around with them sarcastically
just to see their pimpled faces become pale...

Varistor to shield voltage spikes
 

"w_tom" wrote in news:1137400018.457647.150500
@g44g2000cwa.googlegroups.com:

A sales person who cannot provide numerical
specs up front is useless for any answers.



Whew! This is a TOUGH bunch...(c;

Glad I'm not a boat broker...

Varistor to shield voltage spikes
 

Len wrote:
Hi group,

I want to use a welding machine on board and power it with my onboard
6 kW generator. The welding machine is a AC/DC HF-TIG with a lot of
electronics inside. I have no documentation of my generator so I
wanted to deal with the possibility of voltage spikes fi directly
after stopping the welding-arc.

My ships chandler gave me the following advice:
In the power cord add an automatic fuse. Directlly after the fuse
connect the phase and the null using a 235v Varistor. Under 235 volts
it'll maintain high resistance and all will function normally. When
the voltage exceeds 235 it will short circuit and the fuse will break
the connection.

What do you think of this setup. Will it operate fast enough to really
prevent a voltage spike to reach my welding machine?

Regards, Len,
S/v Present

What kind of metal do you want to weld? Alu or steel or stainless steel?
Most power you wil need for ALU. For 10mm alu you wil need 500amp AC
high frequent.
So if you will weld at 80% of the max, I don't think you wil have a problem.


--
Geert Maene.