All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > General Electronics Chat

Notices

General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 11-30-2010, 01:15 AM
TheLaw TheLaw is offline
Senior Member
 
Join Date: Sep 2010
Posts: 228
Default Choosing a MOV for a AC transient/surge filter?

Hey guys,

I have a question regarding MOVs...

So I want to put a transient filter on my power supply, but I don't know how to choose a MOV because their ratings don't make sense to me.

I think a transient filter (surge suppressor), should look something like this:



RV1 is the varistor (MOV). It doesn't make sense because by nature I thought the voltage rating should be around say 200V and the clamping voltage around 135V (US 120V Power).

But it turns out that if I wanted a MOV with a clamping voltage of 135V, then it would only be rated for about 40V continuous....

I'm utterly confused. What should the value(s) of RV1 be?

Thanks.
Reply With Quote
  #2  
Old 11-30-2010, 01:52 AM
retched's Avatar
retched retched is offline
Senior Member
 
Join Date: Dec 2009
Location: Baltimore, MD
Posts: 5,198
Blog Entries: 14
Default

Maybe this will help clear some things up for you:
http://www.galco.com/circuit/TechTips-MOV.htm
__________________
-rm-
Reply With Quote
  #3  
Old 11-30-2010, 02:46 AM
TheLaw TheLaw is offline
Senior Member
 
Join Date: Sep 2010
Posts: 228
Default

That's an excellent link but I'm still confused. Google isn't helping me too much. I can't find too many good results...hmm...
Reply With Quote
  #4  
Old 11-30-2010, 02:58 AM
TheLaw TheLaw is offline
Senior Member
 
Join Date: Sep 2010
Posts: 228
Default

Okay so I guess I figured it out. The AC value shouldnt be like 130, it should be closer to 170V which is the peak AC you can get from the wall.

The clamping volting would be more around 400-600V not like 175V.
Reply With Quote
  #5  
Old 11-30-2010, 06:45 AM
timrobbins's Avatar
timrobbins timrobbins is offline
Senior Member
 
Join Date: Aug 2009
Location: Melbourne, Australia
Posts: 318
Default

Wiring anything to the mains without fully understanding the operation and the consequences with respect to safety and damage and protection is not a good idea.

That said, why do you want to add a filter/supressor?
Reply With Quote
  #6  
Old 11-30-2010, 02:09 PM
TheLaw TheLaw is offline
Senior Member
 
Join Date: Sep 2010
Posts: 228
Default

Well if I follow the wiring diagrams for the transformer and use components with the proper ratings...what could go wrong, in theory?

I want to add a surge supressor, just to have means of protection and to add something to it.
Reply With Quote
  #7  
Old 11-30-2010, 07:17 PM
timrobbins's Avatar
timrobbins timrobbins is offline
Senior Member
 
Join Date: Aug 2009
Location: Melbourne, Australia
Posts: 318
Default

A design would normally come with specified parts, to work with a defined input supply and load. Were you planning to use common-mode chokes and line to earth caps, and do you have their specs?

Is your mains supply prone to any particular disturbance, and is it well regulated, and is it deep in a domestic wiring environment or sitting at the incoming distribution? Do you have a special bit of equipment you want to protect, or is just to give you a good feeling? Are you going to regularly check that the MOV is still functioning, or will it be tucked away out of site only to looked at after you hear a bang or smell something burnt, or open it up in 20 years time? Are you worried about earth potential rise stresses? These are some typical issues affecting the choice of MOV.

Ciao, Tim
Reply With Quote
  #8  
Old 11-30-2010, 09:18 PM
TheLaw TheLaw is offline
Senior Member
 
Join Date: Sep 2010
Posts: 228
Default

Alright, that was fairly discouraging. But in a good way. I barely put any thought into any of those questions. But a question I do have is.. if I can use a wall transformer brick and then wire a power supply to it?

That would hopefully eliminate or reduce the chance for catastrophic disaster.

The power supply is intended to put out maybe 1-2A of power. Nothing big.
Reply With Quote
  #9  
Old 11-30-2010, 11:18 PM
TheLaw TheLaw is offline
Senior Member
 
Join Date: Sep 2010
Posts: 228
Default

Now that I reread your post, I'm not thinking that wiring up a mains power supply could be that hard/dangerous. I suppose if I put a fork into the outlet while plugging it in, I could potentially do some damage, but I am trying to think, "What could really happen?"

The input protection that I want to put on the supply is really for no good reason, other than to have it. Is it crucial? Not at all. I just want it to power some of my own small projects. It's not going to be powering anything more than a board with a Atmel or Microchip MCU on it.

Checking the varistor and all the other things...Again, its not a very important supply. If something goes wrong, no one's life will be on the line (as of now).

So, yeah....maybe I'll re-think this.
Reply With Quote
  #10  
Old 12-01-2010, 07:35 AM
timrobbins's Avatar
timrobbins timrobbins is offline
Senior Member
 
Join Date: Aug 2009
Location: Melbourne, Australia
Posts: 318
Default

Sorry - I didn't mean to be discouraging - but rather to make you think through the topic and hone in what you really need. Forums are good to then zero in on a particular issue. For example, if your concern was an expensive uP circuit, or small projects powered from DC, which you didn't want to go over-voltage, then it's a good idea to firstly focus on the power supply that generates your DC and appreciate how it could go over-voltage, and what level of voltage could cause failure. It's a great topic, and makes you appreciate the energy in transients and how transients may or may not lead to a failure.
Reply With Quote
Reply   Post New Thread

Tags
, , ,


Related Site Pages
Section Title
Worksheet Clipper and clamper circuits


Similar Threads
Thread Thread Starter Forum Replies Last Post
Digital code lock using lcd and keypad naspek The Projects Forum 0 08-22-2010 03:52 AM
seven segment display electronicslover The Projects Forum 29 04-24-2010 10:37 AM
Traffic Control System - 8051 hira287 Embedded Systems and Microcontrollers 0 05-08-2009 12:44 PM
microcontroller programming in asm priya_rm Embedded Systems and Microcontrollers 10 06-22-2008 08:20 AM
I need a help in Assembly language samara Programmer's Corner 12 06-06-2008 10:55 PM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 09:25 AM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.