# Electrical question (RE: Varistors) **URL:** \ **Category:** Factual Questions\ **Created:** [August 12, 2008, 11:07pm UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787 "2008-08-12T23:07:48Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [August 12, 2008, 11:07pm UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/1 "2008-08-12T23:07:48Z")
There is a varistor on the main power (110v AC) to my pinball machine. It went bad. Can’t find one local\* and don’t expect much luck getting quantity _one_ online. The search will continue, however. The varistor is “upstream” of the fuse, so there is protection to the expensive bits provided. Assuming the extream unlikelyhood of lighting strikes/voltage spikes (the machine is plugged into a surge protector anyway) can I just bypass this thing? Either temporaraly or permenantly? Is this a bad idea? I’ve been reading on the net that this thing doesn’t do to much under normal circumstances. I turn the maching off when not playing (the varistor is between the switch and the fuse). What do ya all think, those of you who are more learned on the subject? \*Could start a Pit thread on this, I tell ya! ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 12, 2008, 11:23pm UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/2 "2008-08-12T23:23:51Z")
If the machine doesn’t work without the “varistor” it probably isn’t one. Surge suppressors are installed in parallel with the supply voltage, and the machine will work without them installed. It sounds like you have a bad inrush-current limiter like [these](http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=656273;keywords=inrush%20current). Does this make sense? What machine is this? I have schematics for Williams machines of 1980s vintage. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 12, 2008, 11:25pm UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/3 "2008-08-12T23:25:20Z")
Why not just replace it? They’re cheap enough. But, if you must, sure, you can just remove it entirely and the device (assuming no other problems–which may be a stretch; varistors just don’t “go bad” normally unless excessive surge energy has killed them) should function normally, albeit, with no surge protection. To compensate for that, you could just plug the pinball machine into a dedicated surge supressor–probably not a bad long-term solution, either. ---
**Author:** ![HongKongFooey](https://avatars.discourse-cdn.com/v4/letter/h/c4cdca/32.png) [@HongKongFooey](https://boards.straightdope.com/u/HongKongFooey)\ **Post date:** [August 12, 2008, 11:25pm UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/4 "2008-08-12T23:25:38Z")
My question would be why did the varistor fail? If it’s an old machine maybe it just degraded but usually when a varistor goes bad it’s because it has been overheated due to sustained current through it, at least that’s been my experience. Is it connected across the line and failed closed? If that’s the case you can just remove it to bypass it, but I would at least look for another one just in case it failed because it was absorbing transient volatges. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [August 13, 2008, 12:16am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/5 "2008-08-13T00:16:14Z")
[QUOTE=beowulff] If the machine doesn’t work without the “varistor” it probably isn’t one. What machine is this? I have schematics for Williams machines of 1980s vintage. [/QUOTE] The varistor is actually broken, so the connection is lost. It did work, intermittingly (sp) till I discovered what the problem was. It is a Williams Dracula, however, the parts in question appear to be a retrofit from a European 220v changeover back to 110. I’m not smart enough to understand the info on your link. ☹ ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [August 13, 2008, 12:20am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/6 "2008-08-13T00:20:11Z")
[QUOTE=Q.E.D.] Why not just replace it? They’re cheap enough. [/QUOTE] If you can find one! Thats the problem. I live in the middle of nowhere. No one has one locally, and I doubt I can buy \*quantity one \* online even when I do find one. Yeah. I can afford hundreds. Thats probably what I’ll have to buy, too. I’m looking to avoid that. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 13, 2008, 12:20am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/7 "2008-08-13T00:20:53Z")
[QUOTE=Gatopescado] The varistor is actually broken, so the connection is lost. It did work, intermittingly (sp) till I discovered what the problem was. [/QUOTE] Then it’s not a varistor. A varistor is connected in parallel with the device under power and provides a shunt path for excess voltage–it works by being a **var** ying res **istor** with a resistance inversely proportional to the applied voltage. Removing it makes no difference in the operation of the device under load, except to the extent that it’s no longer protected from voltage spikes and surges. Can you provide a photo of the component in question? ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [August 13, 2008, 12:25am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/8 "2008-08-13T00:25:20Z")
[QUOTE=HongKongFooey] My question would be why did the varistor fail? [/QUOTE] My kid was playing with the switch, flipping it rapidly on and off. The little disk has a black spot and the lead has come away from the disc. It works intermittently till the slightest bump, the the machine goes dead, and usually comes right back on. Doesn’t make for very good play to say the least. I think I’m just gonna by-pass it and see what happens. Hopefully the fuse will protect me. :eek: If not, the machine is only worth about 3k. :smack: Thank you all for the responses! ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 13, 2008, 12:26am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/9 "2008-08-13T00:26:54Z")
[QUOTE=Gatopescado] I think I’m just gonna by-pass it and see what happens. [/QUOTE] I would absolutely NOT do that. Not until I know what it is. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [August 13, 2008, 12:34am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/10 "2008-08-13T00:34:45Z")
[QUOTE=Q.E.D.] Then it’s not a varistor. Can you provide a photo of the component in question? [/QUOTE] Thats what the “Oh So Helpful” people at the electronics store told my wife it was, but they are the same people who didn’t have one, couldn’t/wouldn’t order one, offered no alternatives or advice where to find one, either. :rolleyes: I’ll try to shoot you a photo later tonight. Thanks for the help so far… ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 13, 2008, 12:41am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/11 "2008-08-13T00:41:05Z")
Based on [this](http://www.ipdb.org/files/3072/Williams_1993_Bram_Stoker_s_Dracula_Parts_List.txt), it’s an in-rush current limiter, like I suspected. It’s pretty unclear what the correct value is (other than the current, which is obviously 8A, but [this](http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=KC003L-ND) would be my guess (8A, 2.5Ω at room temperature). There’s a little discussion of it [here](http://newsgroups.derkeiler.com/Archive/Rec/rec.games.pinball/2008-01/msg18580.html). ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [August 13, 2008, 12:50am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/12 "2008-08-13T00:50:11Z")
[QUOTE=Gatopescado] If you can find one! Thats the problem. I live in the middle of nowhere. No one has one locally, and I doubt I can buy \*quantity one \* online even when I do find one. [/QUOTE] Once you determine the specs you may need, try Ebay for your parts. You might have to search a bit and drop $5-15 but you’ll get a handful and it is still cheaper than the larger online suppliers with higher minimum orders. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 13, 2008, 12:53am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/13 "2008-08-13T00:53:19Z")
[QUOTE=beowulff] Based on [this](http://www.ipdb.org/files/3072/Williams_1993_Bram_Stoker_s_Dracula_Parts_List.txt), it’s an in-rush current limiter, like I suspected. [/QUOTE] I think so, too. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [August 13, 2008, 3:42am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/14 "2008-08-13T03:42:17Z")
[QUOTE=beowulff] Based on [this](http://www.ipdb.org/files/3072/Williams_1993_Bram_Stoker_s_Dracula_Parts_List.txt), it’s an in-rush current limiter, like I suspected. It’s pretty unclear what the correct value is (other than the current, which is obviously 8A, but [this](http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=KC003L-ND) would be my guess (8A, 2.5Ω at room temperature). There’s a little discussion of it [here](http://newsgroups.derkeiler.com/Archive/Rec/rec.games.pinball/2008-01/msg18580.html). [/QUOTE] Wow! It is 2.5 Ohm. Its a little silver round disk with this on it: PH NTC 2.5 Ohm (symbol) What number part on that link am I looking for? I went out and looked closer at the assembly. The power cord comes in, black and white go to a switch. Common/green goes to the top of a “UMI Filter”. Black and white go to filter. Black comes out, this “thingy” is in-line, and goes up to fuse. The white splits, with two wires coming out. One jumps over to black with a green “thingy” (looks pretty much like a varistor or whatever were talking about, but is green with a poly-coating. I’ll try to get photos, but with dial-up, even if I get them, you probably won’t. Thanks so far! Edit: Stupid question, again! Can I by-pass this temporarly till I find the part? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [August 13, 2008, 4:01am UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/15 "2008-08-13T04:01:22Z")
[QUOTE=Gatopescado] Wow! It is 2.5 Ohm. Its a little silver round disk with this on it: PH NTC 2.5 Ohm (symbol) What number part on that link am I looking for? I went out and looked closer at the assembly. The power cord comes in, black and white go to a switch. Common/green goes to the top of a “UMI Filter”. Black and white go to filter. Black comes out, this “thingy” is in-line, and goes up to fuse. The white splits, with two wires coming out. One jumps over to black with a green “thingy” (looks pretty much like a varistor or whatever were talking about, but is green with a poly-coating. I’ll try to get photos, but with dial-up, even if I get them, you probably won’t. Thanks so far! Edit: Stupid question, again! Can I by-pass this temporarly till I find the part? [/QUOTE] It’s a 2.5Ω (at room temperature) NTC (Negative Temperature Coefficient) Thermistor. [This](http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=KC003L-ND) should work. I wouldn’t bypass it - you are likely to blow your fuse Buying a single item from Digi-Key is going to be expensive - you might want to check with a local electronics store. Ask for an 8 Amp 2.5Ω @ 25°C inrush current limiter. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [August 13, 2008, 3:04pm UTC](https://boards.straightdope.com/t/electrical-question-re-varistors/459787/16 "2008-08-13T15:04:29Z")
You guys rock, Thank you.