#1777

[@pvc988]

There is often a hole in the board where these once were.

[@lmamakos]

Good board layout tip!

[@JaenEngineering]

The problem with thinking of these in terms of diodes is when they breakdown, they don't maintain a voltage across them like diodes would, they actually breakdown and become a short so they're more like a solid state version of a gas discharge tube.

[@tripplefives1402]

They also tend to not reset if they get hot when shorted. They are used in surge strips for example and typically will no longer work after the first time being activated. In fact, the surge strips tend to melt to the floor.

[@KNfLrPn]

Why didn't the curve tracer show that?

[@Peter_S_]

@@KNfLrPn The dead short effects are felt at higher currents. You'll very commonly see MOVs inline with a thermal fuse in power strips. Many power strips also include a "protection active" light which is just a indicator wired across the MOV, but still in series with the thermal fuse. I remember an old GE datasheet saying MOVs can explode upon repeated application of surges, but they used more corporate compatible wording.

[@WhiteBream]

They don't, unless worn out due to too many absorbed surges, in which case their leakage current will increase. Until popping due to dissipation. A TVS diode becomes a short too when overloaded. Once triggered, a GDT drops to ~20V or thereabout and remains there until the current drops below the hold current. That's why so see varistors on mains power supplies and no GDT's.

[@WestCoastMole]

Mark can you furnish us with the URL for the Tech Note you cite ?

[@Peter_S_]

MOVs were employed as variable capacitors in the stereo vibrato circuit of the Magnatone 280 guitar amplifier used by Buddy Holly. Fender included a more basic tremolo function in their amplifiers and called it vibrato, but the true vibrato of the Magnatones has cemented their place in history. It should also be noted that MOVs degrade as they absorb spikes are thus limited lifetime components. My favorite GE MOV datasheet read, "Upon repeated application of surges, the MOV may expel its internal components in both solid and gaseous form."

[@goodun2974]

One type of early varistor was made with copper oxide; Magnatone used them for the patented pitch-shifting true electronic Vibrato circuit in their guitar amplifiers (other amplifiers claiming to incorporate "vibrato" are merely tremolo circuits, only a few of which generate sufficient phase shift to sound somewhat like pitch-shifting vibrato.) I believe the Magnatone varistors were a custom mde device and are no longer available.

[@bobbauvian7700]

thank you, perfect explanation. this is the first time I got what these things do and now I know how to use my probe around them.

[@tedivester4947]

The company I worked for out of college manufactured a "safety analyzer" that tested for current leakage on DUTs in the medical environment. On the top of this device was a 120VAC receptacle that the DUT would plug into. One test required the polarity of the test receptacle to reverse. This was done with a push of a button. When a high inductive device was plugged in and the button was pushed, there was sometimes violent a "Ka-Boom". There were 2 MOVs across the test receptacle and they would blow up in a spectacular fashion, causing the poor technician hours of work cleaning up. I remember MOVs.

[@davebleamwa2bxy799]

I used your tester for 12 years. Ours had a fault detector breaker that would kick the load off and re-set the tester, so no explosions and foreign matter in the OR.

[@tedivester4947]

That would have been an interesting feature. If I remember right, the model was a Neurodyne Dempsey 431. I worked there for 3 years and moved on to work in a hospital in Sacramento using the same equipment. Retired around 35 years later in a small hospital in NE Oregon.@@davebleamwa2bxy799

[@jms019]

Problem is doing their job knackers them and it’s impossible to tell how knackered they are. I love your diode explanation as had never thought of them this way.

[@simontay4851]

What is the difference between a MOV and a TVS diode. Please can you look at some TVS diodes on the curve tracer.

[@tripplefives1402]

Typically a TVS diode is like back to back zeners.

[@BjornV78]

@@tripplefives1402 , only a Bi-directional TVS diode acts like a back to back Zener. A uni-directional TVS diode acts like a normal single Zener.

[@bigjd2k]

You can get an MOV and fuse combined in one device. Says it all really!

[@inductr]

Insulation tester is handy to test MOV, just with a multimeter reading DC across it. The tester is limiting the current and the reading is the voltage drop.This is a quick & effective test.

[@inductr]

ps also found this useful "Transisitor withstand voltage tester" (120-2700V and 0.2-3.8mA) which I also use for zeners etc

[@rahulkushwaha9500]

can you put a TVS diode on your curve tracer, please :)

[@Blackened-h7n]

Super interesting analysis and explanation of how do those things work! And of course, your curve-tracing of different electronic parts is excellent! Thanks a lot!

[@tiagoferreira086]

These are really useful devices, however they have a BIG drawback, they wear out with the number (energy dependent) off peaks they absorb, and they can get to a point when they keep conducting a significant amount of current enough to start a fire due to heating, I've often seen them physically coupled (heatshrink, metal spring, epoxy glued) with a thermal fuse. IF i'm not mistaken there are some laws/standards that obligate manufacturers to use MOV in parallel with the main's input with a series fuse.

[@Indiskret1]

My biggest Belkin surge protectors with around 2700 Joule protection have several MOV-packs (with 4-6 MOV each) with a thermal fuse in between the MOV's, just like you say. One blew up one day after starting a microwave I had connected to it, so I took it apart and checked it out. Probably already on its way out as we have massive thunderstorms in the summers, so it already probably had taken some shock. They have diodes to indicate if the protection is still working or not.

[@tiagoferreira086]

@@Indiskret1 seems like they did their intended job :)

[@BjornV78]

MOV's are Firestarters, in severe overvoltage events they can explode and cause fire. During there lifetime they slowly degrade with each short spike that occurs on the powerline. Therefore i never use MOV's, but use Bi-directional TVS diodes instead. A TVS diode doesn't degrade after each event, and the responsetime of a TVS is in the Nanosecond range, so it will react much quicker. Also, TVS diodes are available from arround 3.6V up to 600V, so not only for low voltage like many sites on the net say.

[@mikesradiorepair]

If your worried about fire hazard then use TMOV / TPMOV which are thermally protected MOV's. They disconnect when they reach a set temperature. All the big MOV manufacturers like Eaton and Littlefuse make them.

[@tripplefives1402]

The problem with diodes is that ones large enough to contain a surge on mains without just blowing up immediately are pretty expensive. Diodes typically blow so fast that a fuse or circuit breaker won't trip fast enough and they usually fail shorted so its still going to burn some wires or traces. For use on mains you probably want 10W rated diodes or higher.

[@BjornV78]

@@tripplefives1402, even a TVS diode in SMD package can withstand up to 600V and peak surge of 1.5Kw. Take a look at the 1.5SMC300CA from Littelfuse. This type can handle 300V at 1.5Kw surge and cost arround $1.

[@Peter_S_]

@@mikesradiorepair Better to just toss the MOVs in the bin and use Vishay TransZorbs instead. TransZorb Transient Voltage Suppressors are superior in every way.

[@mikesradiorepair]

@@Peter_S_ TVS diodes are not suitable for mains protection due to their much lower joule rating. Also, TVS diodes tend to fail instantly in a dead short when they fail and they do not make a automatic disconnect TVS diode. Modern MOV's like I mentioned and currently use do disconnect once they reach their thermal limit. I do use TVS diodes but where suitable, secondary power supply circuits.

[@Tyler-Swift]

I discovered these recently when I wanted to build a rotator cable surge protector for ham radio. Cheap, easy, and quick to build.

[@tripplefives1402]

Make sure you fuse it, because if they get hot while working they melt shorted and burn everything up.

[@fjs1111]

Very interesting indeed!! Isn't this a simplified crowbar circuit when they short and blow the fuse?

[@AdmiralQuality]

I see there's very low voltage ones, down to 3.2V on Digikey. I wonder if any guitar distortion pedals use these instead of diodes for their clipping.

[@pault6533]

Thanks for showing and explaining these! I am smarter watching your frequent posts. I have to figure out how to turn my little handheld oscilloscope into a curve tracer....

[@IMSAIGuy]

diy curve tracer: kzbin.info/www/bejne/pXerhYKHia6caZIsi=fadcMbbHTO1ngGBA

[@SeanBZA]

Those are not zinc oxide, as the zinc oxide ones tend to be pretty resistive, so the slope with current rises quite high. Likely other metal oxides blended, and sintered. I have had a few NOS GE Zinc oxide varistors that I got as a pack, and used a few over the years. Red dipped epoxy on them. They will all eventually fail when used on the mains, simply because the constant spikes degrade them, so for mains use it is always recommended to use the ones with 3 wires, which have a single shot thermal fuse integrated into the epoxy dip, so that when they cook themselves to a short the fuse disconnects the MOV element from the supply. I have had, in that pack of NOS, one that developed a blister sitting in the pack, and on testing it turned out to be short circuit completely. The ones in service also do need regular replacing, they give themselves up to protect against surges, and then either blow open completely, for the small devices, that get way too much energy in (though they are great if used after a resistor in a capacitive dropper, or with a small transformer after inrush limiter resistor to provide protection, using a fusible resistor) or, for the larger ones, they simply go short circuit when the silver layer diffuses through the device. I use them a lot on LED lamps, it does help with taming surges, though I also had a photocell with built in MOV protection that landed up on 350VAC mains, and that one failed, blowing up, and blasting the plastic cover of the photocell up high, and shattering it in the process as well. Fun thing is that all street light photocells have a massive MOV in them, both in the fixture itself, and also in the photocell, even the shorting cells have one built in.480V operation, so they are there for lightning surge protection, as they will not trip if the neutral fails, and the one set of lights ends up sitting across phases. A lot of those electronic ballasts will survive operating on 400VAC, even though they are only rated to run from 120VAC to 277VAC. Magnetic ones do not care at all, they are designed to not fail with shorted bulb and 400VAC across them, though they will eventually fail from long term use, but a few days till fixed no problem.

[@goodun2974]

Some early varistors were made with copper oxide composition, and one type that might have been a custom part was used by Magnatone for the patented, unique pitch shifting true vibrato circuit built into some of their amplifiers. Virtually all other amplifier brands incorporated tremolo and not true vibrato.

[@egeotomasyon]

MOV Metal Oxide Varistor

[@kwazar6725]

I was gonna say that. I ran across them doing smps and when back emf from brushless motors needed clamping

[@IMSAIGuy]

yes varistor

[@wjniemi]

I used a lot of these to protect electronic control equipment in factory settings. It seems as if there was some finite number of hits these can take before they stop protecting. (Permanently open?) Some of them were big honkin' plastic trapezoid shaped devices rated in thousands of joules.

[@AIJenkins]

Thanks for sharing this with us. I’m going to experiment with these now. 😊

[@guytech7310]

Try same test using a GDT (Gas discharge Tube) & a TVS Diode. I would be curious to see the graph for a GDT on your meter.

[@IMSAIGuy]

it will be similar to this: kzbin.info/www/bejne/p5fJgYNuZbd9oNksi=EbN4VoQycscwCFyA

[@JimmyBagOfDonuts]

I ❤ Chip of the Day

[@qutube100]

Love the "will it curve trace" series, awesome!

[@bobbauvian7700]

I have a question. in CA where power keeps going out during windy seasons for the last several years now. I see many clients electronics going bad. there was one time where 6 power supply went out in a lab of 20. what do you suggest to protect against that, a power line conditioner or an inline power surge protector like a power strip? I think there were power strips with surge protectors there, but they did not help.

[@Matsuiiiiii]

Hi. Like your chip of the day series. Would love to hear some insight on solid state relays/opto's like the LH1516 and LH1056. Very useful and cheap cuties.

[@Centar1964]

I wonder how these would perform in an RF application, for example variable capacitor flashover protection...

[@MrPeplonski]

What are the advantages over TVS-Diodes? I was designing replacement electronic for a device that needed to switch an inductive load. The original electronic implemented a varistor as a snubber just like you mentioned. I was wondering if I could get away with a TVS Diode instead for cost reasons. But decided to go with a mov like the original

[@Savan_Triveda]

Very interesting. Thank you.

[@chrisscott1547]

"Back to back zener diodes" (Parallel ?) I think you meant to say series-connected zeners as they will readily forward conduct at low voltages ... A $3 Mov is often the only device in cheap "surge protector" outlet strips. They work pretty well, but their massive capacitance can limit clamping speed. They will explode with too much energy.

[@xXsch3ricXx]

Can someone please explain why the safety breaker doesnt trigger when the mov is in active state / looking like a short across the mains ?

[@billdegener8105]

What about overpowering a smaller one with a series bulb and capture the destruct?

[@EJEuth]

Very interesting. Could you share the link for that printed info you have shown? Thank you for the video!

[@IMSAIGuy]

components101.com/articles/metal-oxide-varistor-mov-overview

[@y_x2]

MOV are rated in Energy (in joule) not in power dissipation. Energy = Power x time

[@jp040759]

I don't have access to a curve tracer but was wondering if i could use an Insulation tester to confirm the breakdown voltage of an MOV. The are supposed to only deliver 1 milliamp of current when they breakdown. SO I would think that would not destroy the MOV once it hits breakdown. The tester displays breakdown voltage. I could reverse the polarity to test in the opposite direction. I don't know of a simpler way to generate up 1000 to 1200 volts for testing MOVs, diodes, (1N4007) or TVS breakdown voltages. Thoughts anyone???

[@davidv1289]

Everyone loves Chip of the Day. Thank you for an interesting video, I had not seen one on a curve tracer. As others have asked, how about a TVS? Regards, David

[@robinbrowne5419]

A cool and interesting video. It is amazing what these chemicals/compounds can do 👍 But I find it a bit strange that the manufacturer shows a diagram with no fuse (at 2:08). Is this a disaster waiting to happen?

[@charlesdorval394]

Quite interesting, Thank you!

[@kenchorney2724]

MOV's seem to change their characteristics when they absorb energy. Small spikes over the years seem to lower their resistance and they can become heaters. Some fire departments in the US have tried to generate awareness of the fire hazard they can present when used in cheap "surge protected" power bars (likely they are too small in energy absorbing capacity and/or not adequately fused).

[@mikesradiorepair]

If your worried about fire hazard then use TMOV / TPMOV which are thermally protected MOV's. They disconnect when they reach a set temperature. All the big MOV manufacturers like Eaton and Littlefuse make them.

[@tripplefives1402]

Even expensive ones have typically just a MOV soldered directly to the mains and will start a fire if not fused or if the surge comes from the load side, like lightning. Also if a large enough surge hits them they'll start a fire even in the short time it takes the fuse to burn.

[@mikesradiorepair]

You don't have that problem with TMOV/TPMOV's. Different versions use different mechanisms to disconnect but they are thermally operated. Once it opens it's open for life. The Littlefuse versions can be gotten in 2 and 3 lead versions. The 3 lead version allows the monitoring of the TMOV. If it opens the third lead is used to monitor that and alert. @@tripplefives1402

[@pauldery7875]

Thank you so much, I would have never know, how these work. My complements to the chef. Lol

[@bobdoritique7347]

Merci for this video.

[@PuchMaxi]

I have seens MOVs used in place of a fuse, it seemed a bit odd to me?

[@IMSAIGuy]

you are thinking of these: kzbin.info/www/bejne/m5bEoqx6aL-MoKssi=F42kCw0R8BmbgWJr

[@PuchMaxi]

@@IMSAIGuy Thanks! You are right, they are PTCs.

[@orion310591RS]

If you use this component, put heatshrink on it. It can explode and act like fireworks, search for videos of it being destroyed.

[@byronwatkins2565]

ZnO is a wide gap semiconductor, so 3-4 V each instead of 0.7 V...

[@Linguae_Music]

If they make low voltage varistors, then these could be really cool for some waveshaping in an audio circuit!!! I don't know if they do but i am about to google it!

[@Linguae_Music]

Welll.... They make low voltage ones..... but not low enough lmao So i guess not xD I guess i can just use diodes like a normal person lmaoooo (I'm not smart yet, dont judge me lol)

[@goodun2974]

Magnetone guitar amps of the 1950s and 60s used a special copper oxide (perhaps custom made) for their patented, unique electronic pitch shifting vibrato circuit in their amps. Nearly all other guitarr amps that claim "vibrato" are merely using a tremelo circuit and only a very few have sufficient phase shift that they start to sound like there is a vibrato effect happening as well. You can find plenty of information online about the Magnatone vibrato circuit and the orginal patent belonging to Dan Bonham. As far as I know, the original devices have not been manufactured for years and I don't know of any substitutes, but fortunately they almost never fail even in a 60-year-old amplifier. The Magnatone name has been bought by another company who is building amplifiers with that logo, but I don't know anything about the dedign and I'm betting that they're not using the original patented circuit....

[@surgingcircuits6955]

Good Stuff

[@John-pp2jr]

Varactor?

[@IMSAIGuy]

varistor

[@dennisfahey2379]

Great explanation! I've seen these for years and honestly never even gave their chemistry a second thought. Shame on me. Question - do you know of any orgs or meetups for retired engineers who want to take their wealth of experience and do projects for the public good? Seems like a waste of collective brilliance and passion.

[@keithking1985]

I thought they were called varistors. And i thought a varactor was diode wit a capacitor built in. Am i wrong.??? Oh 😮😢 SORRY I HEARD YOU WRONG AT THE BEGINING... 😅

[@IMSAIGuy]

varistor

[@666sajad]

😍😍😍😍😍😍😍🥰🥰🥰🥰🥰🥰

[@davebleamwa2bxy799]

I used your