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'[EE] choosing a MOV value'
2006\08\08@120431 by alan smith

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Sorta a random question.....
 
 MOV ratings are by voltage...ok im running on 120VAC so choosing a 130Vrms device should be fine.  What about figuring out what  max peak current you should design to, and of course along with that the max energy it can handle.
 
 The application is on the off line power supply design, its going to plug into a wall socket.  The MOV is there to absorb transients on the AC lines, there are no large inductive loads so to speak on the system.  Safest is to choose the biggest baddest I suppose, but needing to conserve space...I need to choose the smallest/cheapest.
 
 Just looking for some guidelines.
 
 The devices im looking at are http://www.chemi-con.co.jp/english/catalog_e/top_varistor_e.html   and the C series SMT parts

               
---------------------------------
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2006\08\08@123912 by Bob Axtell

face picon face
alan smith wrote:
> Sorta a random question.....
>    
>   MOV ratings are by voltage...ok im running on 120VAC so choosing a 130Vrms device should be fine.  What about figuring out what  max peak current you should design to, and of course along with that the max energy it can handle.
>    
>   The application is on the off line power supply design, its going to plug into a wall socket.  The MOV is there to absorb transients on the AC lines, there are no large inductive loads so to speak on the system.  Safest is to choose the biggest baddest I suppose, but needing to conserve space...I need to choose the smallest/cheapest.
>    
>   Just looking for some guidelines.
>    
>   The devices im looking at are http://www.chemi-con.co.jp/english/catalog_e/top_varistor_e.html   and the C series SMT parts
>
>                  
> ---------------------------------
> Groups are talking. We´re listening. Check out the handy changes to Yahoo! Groups.
>  
Be careful. a USA/CANADA mains of 115VAC has peaks of 180VAC. Examine
the data sheet very carefully.

--Bob

2006\08\08@125510 by Bob Blick

face picon face


>   MOV ratings are by voltage...ok im running on 120VAC so choosing a
> 130Vrms device should be fine.

Not unless your uncle owns an MOV factory! Choose an MOV that will protect
your circuit, but make sure your circuit can tolerate a generous
overvoltage first. 130 RMS isn't even 185 peak - it'll be conducting under
normal conditions, and you don't want that.

Cheers,

Bob


2006\08\08@125532 by Peiserma

flavicon
face
piclist-bounces@mit.edu wrote:
> Sorta a random question.....
>
>   MOV ratings are by voltage...ok im running on 120VAC so
> choosing a 130Vrms device should be fine.  What about
> figuring out what  max peak current you should design to, and
> of course along with that the max energy it can handle.

<http://www.epcos.com> has some decent application notes, just buried somewhat
on their site. Go to Product Catalog, Nonlinear Resistors, then
Datasheets. Then scroll down to the bottom.

2006\08\08@160953 by alan smith

picon face
ahh..good point, I was thinking 120Vrms, so 130Vrms part...
 
 Another question, along the use of MOV's, I've seen where they are used in place of an RC snubber circuit. Any advantage or disadvantage of using them in that application?

Bob Blick <spam_OUTbblickTakeThisOuTspamsonic.net> wrote:
 

> MOV ratings are by voltage...ok im running on 120VAC so choosing a
> 130Vrms device should be fine.

Not unless your uncle owns an MOV factory! Choose an MOV that will protect
your circuit, but make sure your circuit can tolerate a generous
overvoltage first. 130 RMS isn't even 185 peak - it'll be conducting under
normal conditions, and you don't want that.

Cheers,

Bob


2006\08\08@162909 by Richard Prosser

picon face
On 09/08/06, alan smith <.....micro_eng2KILLspamspam@spam@yahoo.com> wrote:
> ahh..good point, I was thinking 120Vrms, so 130Vrms part...
>
>  Another question, along the use of MOV's, I've seen where they are used in place of an RC snubber circuit. Any advantage or disadvantage of using them in that application?
>
> Bob Blick <bblickspamKILLspamsonic.net> wrote:
>

Alan,
Movs do have a wearout mechanism so dependent on energy levels and
repetition rate you could run in trouble over a short time period. If
you're using a MOV as a snubber I'd be tempted to use one much larger
than otherwise indicated.

Re the voltage question - they can be rated for AC operation - so the
"130V" rating may be OK for 110V operation. We have used 275VAC MOVS
on 230V systems (& been caught out when the AC mains exceeded this
value - In China).



Richard P

2006\08\08@170920 by alan smith

picon face
My thought of using the MOV was because the cap for the snubber has to be AC rated, and they are rather large.I'm just out of room for that.

Richard Prosser <.....rhprosserKILLspamspam.....gmail.com> wrote:  On 09/08/06, alan smith wrote:
> ahh..good point, I was thinking 120Vrms, so 130Vrms part...
>
> Another question, along the use of MOV's, I've seen where they are used in place of an RC snubber circuit. Any advantage or disadvantage of using them in that application?
>
> Bob Blick wrote:
>

Alan,
Movs do have a wearout mechanism so dependent on energy levels and
repetition rate you could run in trouble over a short time period. If
you're using a MOV as a snubber I'd be tempted to use one much larger
than otherwise indicated.

Re the voltage question - they can be rated for AC operation - so the
"130V" rating may be OK for 110V operation. We have used 275VAC MOVS
on 230V systems (& been caught out when the AC mains exceeded this
value - In China).



Richard P

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