Talk:Varistor

message: There are two significant differences between the Varistor and a silicon Transient Voltage Suppressor(TVS).  Varistors are typically an order of magnitude more leakier, ie they will drain a battery 10X faster.  Also they degrade over time.  This shows up after repeated transient events.   Mike
:Incorporated. Mike: you could have done that yourself. -- Tim Starling 03:22, Oct 24, 2003 (UTC)
:What about the other figures of merit? Capacitance, max. energy, etc.?-- Tim Starling 03:26, Oct 24, 2003 (UTC)
I think the comparison is incomplete/misleading, at best.  Because MOVs are a bulk-effect device, they tend to be able to absorb more surge energy (joules) for a given size package.  A diode-derived design puts all the action at a junction, an inherently thin slice of the device, concentrating the energy/heat that needs to be dissapated, so a diode of a given size is likely to be less able to handle as much energy as a MOV.  (Also, can someone supply some links/references so that we can check the details on leakage etc.?)
This source says that the leakage current is similar:
http://www.lightningtalks.com/LightningProtection.htm
detailed Comparison of Surge Suppression devices
 Metal-oxide varistor (MOV)
 + Up to 70 000 Amps surge
 + Lifetime @ 100 Amps, 8x20 uS pulse shape: 1000 surges
 - Shunt capacitance >500 pF
 - Leakage approximately 10 micro amps
 Avalanche diode
 + Lifetime @ 50 Amps, 8x20 uS pulse shape: infinite
 + Shunt capacitance: 50 pF
 - Low surge capability: 50 Amps @ 8x20 uS pulse shape
 - Leakage approximately 10 micro amps
69.87.203.165 14:11, 9 November 2006 (UTC)
thread_title: Varistor vs. TVS

message: The lede of the article currently contains the following statement:
:and is not a resistor but in fact a capacitor.
This is horsepucky. While many MOVs usually look like capacitors (in the form of flat disks) and have some parasitic capacitance (which can be measured when you're below their threshold voltage), they are most definitely not capacitors in the sense that an Electrical Engineer would typically mean it. Once you're above their threshold voltage, they are primarily resistive, not capacitive. They are non-linear resistors.
If no one objects, I'll (eventually) re-write this part of the lede.
Atlant 11:40, 25 May 2005 (UTC)
replies: text: Of course they're not capacitors. I rewrote the intro. --Heron 16:47, 25 May 2005 (UTC)
replies: text: Thanks! Atlant 23:31, 25 May 2005 (UTC)
thread_title: A capacitor? Hardly!

message: I dont think the varistor acts as a spark gap, but as a non linear resistor as it says in the first line. Under high applied voltage, it does not breakdown like a gap, but merely goes low resistance, maybe the author was thinking of a miniature gas discharge tube (spark gap). Would anyone like to comment before I alter??Light current 18:57, 9 August 2005 (UTC)
replies: text: The "spark gap" line is so rubbish that I can't wait for you to delete it - it's gone. --Heron 20:58, 9 August 2005 (UTC)
thread_title:  Action of Varistors 

message: Can someone add an electrical symbol to the article?
--PeterMarkSmith 08:18, 17 January 2006 (UTC)
replies: text: I would second this motion. --Matejhowell 22:26, 22 February 2006 (UTC)
replies: text:  Should the 'Traditional varistor schematic symbol' shown top right be different from that for a DIAC ? - Rod57 (talk) 18:15, 25 April 2017 (UTC)
thread_title:  Electrical Symbol 

message: I thought that if a Varistor protects a circuit from excessive voltage spikes, etc, then surely the resistance would have to INCREASE with an increase in voltage, not the other way around, as is stated towards the middle of the article. I'm still learning this stuff, so can someone please help? —This unsigned comment was added by 203.87.68.209 (talk • contribs) .
:Varistors are usually hooked up shunting (in parallel with) a load to be protected. If an over-voltage condition occurs, they decrease rapidly in resistance, shorting out most of the energy of the overvoltage (at least until the point where the energy dissipated within the varistor heats the varistor to the point of destruction). The energy of the transient is dissipated in varistor and the source impedance of the voltage rail.
:By the way, you can sign your posts on "talk" pages by including four tildes (~~~~) at the end of your post. When you press "Save page", this will be converted into your username or ip address in a handy Wikilinked format. A timestamp will also be included.
:Atlant 12:32, 28 March 2006 (UTC)
thread_title:  Varistors in shunt or series? 

message: When encountering a surge, I have read that MOVs will sacrifice themselves to protect loaded equipment. If this is true, I think it should be included in the article. Chris 13:06, 30 October 2006 (UTC)
replies: text: I know! I know! It's w_tom.  Lemme do the next one.  —Preceding unsigned comment added by 69.95.190.147 (talk) 15:45, 1 October 2007 (UTC)
thread_title:  Sacrifice? 

message: How can you test your MOV/surge protectors to see if they have been degraded etc?
Ideally, you would first visually inspect the MOVs to see if they appear damaged.  But if they look OK or you cannot get access to them, you can test them electrically.
Ideally, you would do I-V curve tracing under various conditions.  (More information here: http://www.repairfaq.org/sam/semitest.htm )  And you would study the datasheets, such as the pdf here:  http://www.newark.com/NewarkWebCommerce/newark/en_US/endecaSearch/partDetail.jsp;?SKU=09F2091&CMP=KNC-G10000645 )
But if you are just trying to get by, the first thing to do would be to check the leakage current at the highest voltage you can easily and safely attain, perhaps just whatever your ohm-meter puts out.  Beyond that, you could use the power line as a voltage source (120VAC).  You could very carefully check the leakage current, ideally using a current limiting resistor in case the device you are testing is leaky or shorted.  With a rectifier and capacitor, you could generate a higher DC voltage, 170VDC.  With another rectifier and capacitor, you could double that to 340VDC.  Then with a current limiting resistor of about 200K ohms, you would be able to properly measure the nominal VDC of a MOV under a standard leakage current of about 1mA.  The big safety concerns are to make sure nothing has to dissipate too much power and gets too hot or burns up.  To not overload your DMM or other test instrument with over-voltage etc.  And most important, not to get a shock!
:69.87.193.213 00:23, 10 November 2006 (UTC)
thread_title:  MOV Testing 

message: There is no mention yet of the controversy over whether surge suppressors should be used for general household use. While they are often recommended (sales are profitable),
# computer psus already have better protection built in,
# surge suppressors' fire risk adds to destruction of life and property
# the article so far fails to even mention the difference between inductive surges, which is what such units are able to absorb, and near lightning strikes, which they normally have far too small an ability to deal with.
While they're useful for electronics running on portable generators, which do produce surges a MOV can do something about, on a standard low impedance mains supply they're really of little value.
Yes, controversy and argument... but I do think the article needs to acknowledge the real issues, and start by understanding what type of surge an MOV can dissipate, and what it can't. Lack of awareness seems to be most common on this point, and so far the article seems to perpetutate the popular sales line.
Tabby (talk) 15:41, 31 December 2007 (UTC)
thread_title:  Questionable products 

message: GE's MOV was new in 1972 and fortuitously I stumbled across an article by 4 General Electric R&D people that sets forth how you get from "metal oxide" to "polycrystalline diodes-in-bulk" better than anything I knew before.  The ref is: 
Metal-oxide varistor: a new way to suppress transients."
J.D. Harnden, Jr., F.D.Martzloff, W.G. Morris, and F.G. Golden (all
General Electric), Electronics, 9 Oct 1972, p91.
Paraphrasing the article's text:
"The MOV has an encapsulated polycrystalline ceramic body, with metal
contacts and wire leads.  The essential ingredients of the
polycrystalline ceramic are zinc oxide and bismuth oxide.  They are
mixed with proprietary powdered additives (typically cobalt and
manganese oxides) and pressed into disks for sintering at temperatures
over 1,200 deg C.  Because the bismuth oxide is molten above 825 deg C,
it greatly assists in the formation of a dense polycrystalline ceramic
through the process of liquid-phase sintering.  During cooling, the
liquid phase forms a rigid amorphous coating around each zinc
oxide grain, yielding a microstructure of zinc oxide grains that are
isolated from each other by a thin, yet continuous, intergranular phase.
It is this two-phase microstructure that creates innumerable diode
junctions and thus the device's nonlinear voltage-current
characteristics."
That is so pleasing!  I never understood it before.  Would one of you who have worked so hard to build the MOV entry put some of this text into the first main section after the intro, "Metal oxide varistor"?
Jerry-va (talk) 01:30, 8 August 2009 (UTC)
thread_title:  Better description of MOV polycrystalline structure & mfr 

message: This article is focussed almost entirely on MOVs, it seems like the authors did not appreciate the larger scope of the subject and the history that goes back to the 1920s. Kbrose (talk) 15:39, 13 September 2014 (UTC)
replies: text: The article coverage could indeed be expanded. If you have relevant information backed by WP:RS, please feel free to add it to the article. Reify-tech (talk) 21:04, 21 November 2016 (UTC)
thread_title: article scope

message: Two diodes in antiparallel (such as suggested by the circuit diagram) will form a varistor, but with a breakdown voltage that is no higher than the diode threshold voltage (0.2 for Ge, 0.7 for Si). I am pretty certain that should be antiseries. Grab your electronics kit and try for yourself.
This implies that the electrical diagram is just wrong, and that the "DIAC" symbol has a very good reason for not being used anymore.
This will probably influence the explanation of the working of the MOV a bit.
- Jurjen  — Preceding unsigned comment added by Jurjen B (talk • contribs) 19:48, 10 November 2019 (UTC)
replies: text: Are you assuming that a varistor should have a higher breakdown level than just a diode? The breakdown level is certainly a parameter of interest, but it can be changed by using multiple diodes in series for each direction.  For example, varistors used to be constructed with multiple CuO disks for each direction.  This seem quite analogous to the ZnO MOV, as the grains are randomly oriented, providing statistically the same number of "anti-parallel" grain orientations for each conduction direction. And this also provides the same number of "series" orientations, so that the overall breakdown level can be adjusted with the size of the device. Kbrose (talk) 19:07, 12 November 2019 (UTC)
thread_title:  Antiparallel? That should be antiseries! 

message: How do you pronounce "varistor"? It initially looks like 'VAIR - iss - ,tor but when one discovers that it means "variable resistor" one tries va - 'RISS - tor. Please can someone let us know which it is? Thank you. UBJ 43X (talk) 12:04, 8 November 2021 (UTC)
thread_title:  Pronunciation