MOV Failures - Page 1
Forum section: electronics / projects

author: SG-1
author_rank: Regular Contributor
timestamp: October 29, 2010, 09:05:34 pm
content: I need some advice. I am having trouble with this product. We have been using it for years with no issues. The vendor says no changes have been made in the last 7 years. Look at the CTD-2 model.http://www.electromagnetic.biz/Portals/0/Docs/CDT/CTD1%20&%202%20UL.pdfThe MOV is failing in a few units, maybe 1 out of 50 or a 100. This is 20 or 30 units so far. We are experiencing failures on our test floor. Some fail when first energized, others function a few times, then the output goes to 20VDC or 30 VDC some down to 3VDC. The units were removed & bench tested. The output remained at 20 or 30, or 3 VDC. The unit is replaced & the second one works just fine. No external wiring defects. This device is a critical component of our product. No failures can be tolerated.I have some specs for the MOV & capacitor.MOV is a EPCOS / Type (untaped) SIOV- S14K150 / 200 VDC /4500 Imax (8/20 micro S) / 40.0 Wmax (2ms) / Pmax W .60Capacitor is electrolytic 1500 micro-F 250VDCThermister reads 20 ohms at room temperature.The vendor is offering to replace the MOV with a 175 volt model. Or any thing else we desire, for a cost, of course.What think ye ??Thanks in advance for your help.

author: migsantiago
author_rank: Frequent Contributor
timestamp: October 29, 2010, 09:18:44 pm
content: HelloWe've had problems with big capacitors. They were sent from Israel and when they arrived to Mexico City, they were leaking oil. I thought that the problem was that the pressure in Mexico City is different to the air pressure in Israel (or China, the original manufacturing place). The guys who sent them had no problems with them.Just my 2 cents, check if the pressure rating is good enough for your capacitors.

author: Feanor
author_rank: Regular Contributor
timestamp: October 30, 2010, 12:53:45 am
content: I am also guessing capacitors leaking current. Could be just about any element in this circuit though.MOV, capacitor, freewheel diode : - If anyone of those is allowing current to pass then your output voltage may drop.You really need to open one up, get a probe in there and see what all the voltage levels are. Then cut out the electrolytic cap and replace it with one you know is good.Test again.Cut out the MOV and test again. Usual debugging of problems just remove one element at a time till you find the problem.Obviously this will be connected to the mains so take due precautions. Good luck!

author: SG-1
author_rank: Regular Contributor
timestamp: October 30, 2010, 01:06:06 am
content: The problem child has been identified as the MOV. They are shorting out, cause unknown. cut one lead loose from the circuit board and the Cap Trip Device is back in business. The vendor is replacing them & then sending them back to us.

author: SG-1
author_rank: Regular Contributor
timestamp: October 30, 2010, 01:21:43 am
content: Quote from: Feanor on October 30, 2010, 12:53:45 amI do get your point, but I do not understand how a leaking cap will damage the MOV. We think the vendor got some bad MOVs. The vendor says we are doing something wrong. He has repaired about 20 or 30 of these so far by replacing the MOV. He wants to up the voltage on the MOV to 175VAC RMS to stop the unknown problem, that he believes is voltage spikes or transients.I suppose my question really is what is the highest value for the MOV so it can still protect the downstream componets ??

author: Feanor
author_rank: Regular Contributor
timestamp: October 30, 2010, 06:50:59 am
content: If the capacitor is "leaking" (drawing current to ground) the MOV will not be damaged you are right. It will mean a voltage drop across the thermistor and that will reduce your output voltage.As for is a 175V MOV enough protection or not? This is not my field so hopefully someone else also answers this.Your capacitor is rated at 250V so I am guessing that will be ok. Guessing again but the diodes are probably rated for well over 175V so they should be fine. That just leaves your solenoid, the device you are switching on and off.And of course all of this depends on the type of transient being dealt with. If it gets hit by lightning then probably the whole lot will go up in smoke anyway.

author: Simon
author_rank: Unknown
timestamp: October 30, 2010, 08:57:57 am
content: what mains voltage are you supplying this thing ? even with 120VAC RMS supply you are looking at 170V peaks, usually things like MOV's (I'm not wholly familiar with MOV's) will start conducting something more or less small at a little under the rated voltage, the rated voltage being the clamping voltage = the maximum voltage the mov will hold at. I think the MOV voltage is too low

author: Zero999
author_rank: Super Contributor
timestamp: October 30, 2010, 09:21:40 am
content: Check the datasheet, MOVs are normally rated way below their clamping voltage. Some also have their rating given in RMS not DC.

author: SG-1
author_rank: Regular Contributor
timestamp: October 30, 2010, 09:44:13 pm
content: Quote from: Feanor on October 30, 2010, 06:50:59 amYou are correct, the thermister is choking off the output voltage. The MOV mode of failure is a short or very low resistance. The solonoid ( actually a clapper ) is very robust. It is only activated to open a large circuit breaker. It is energized for 34 milli-seconds & then de-energized again. Of course there can be some very nasty things happening during that time on the medium voltage side.

author: SG-1
author_rank: Regular Contributor
timestamp: October 30, 2010, 09:59:10 pm
content: Quote from: Simon on October 30, 2010, 08:57:57 amThe normal supply voltage is 120VAC RMS.The MOV voltage rating of 150V is given in RMS. I see I missed that in my OP.

author: Simon
author_rank: Unknown
timestamp: October 30, 2010, 10:23:10 pm
content: maybe you need to remove a mov and test it separately, if it's faulty/incorrect you need to ask your supplier some serious questions

author: SG-1
author_rank: Regular Contributor
timestamp: October 31, 2010, 05:10:09 am
content: Quote from: Simon on October 30, 2010, 10:23:10 pmThe MOV has all the right numbers printed on them. I like your suggestion, then send it back to him for replacement, either way. We have been beating on him pretty good. My boss just keeps telling him that he is not the only supplier. I wanted him to test the unit at 150VAC RMS for a few seconds. The inital reply was that any more than 130 would damage something ( unspecified something ). He then asked if our spec had changed. I then clobbered him with his own spec from his own website. Clearly states the device can withstand 140VAC RMS continously. They will now raise the test voltage to 145 VAC RMS. Will they have any in-house failures ? Would they tell me if they did ?? They seem willing to work with us. I think they may have been testing at 120 volts...I found a 14 volt MOV here at the house & ran an experiment of my own to see where the clipping starts.The circuit consists of the MOV in series with a 10K resistor.VINPUTVMOV14.0 14.015.0 15.118.0 17.425.0 19.992.5 24.6 resistor smoking, smells bad in here155 25.4 need new resistor155 volts is the top of that power supply. I think I can get more out of the Rotek. Plenty of resistors in-house. Actually for that last shot I wrapped the resistor in some C130 rubber splicing tape, nice thick tape. Then added a wrap of Permecil, 600 volt tape that is super tough. The resistor still smelled bad after the pop.

author: Time
author_rank: Frequent Contributor
timestamp: October 31, 2010, 05:14:35 am
content: The obvious answer is to test the MOVs by themselves. I do not know why this thread made it this far without actually doing so!

author: Simon
author_rank: Unknown
timestamp: October 31, 2010, 08:39:24 am
content: you needed a proper QC inspector to point you on you way

author: Zero999
author_rank: Super Contributor
timestamp: October 31, 2010, 09:38:07 am
content: Your tests reveal that the MOV starts clipping around 17V which is approximately the rated voltage plus 20%; this confirms what I initially thought so if the MOV is rated to 130VAC, it shouldn't clip until 156VAC or 221VDC.Did the MOV get hot?What power rating was the resistor? Let me guess 0.25W?No wonder 130V (1.7W) killed it, next time use 9 resistors, three paralleled stings of three in series. Resistors may be cheap enough to be disposable but operating them above their maximum ratings can change their value causing the current to be unpredictable.

author: SG-1
author_rank: Regular Contributor
timestamp: October 31, 2010, 10:47:10 pm
content: Quote from: Time on October 31, 2010, 05:14:35 amThe vendor says he can do this, but it will result in a substantial price increase. I think if he uses the correct test voltage for the finished product that would suffice.

author: SG-1
author_rank: Regular Contributor
timestamp: October 31, 2010, 11:14:00 pm
content: Quote from: Hero999 on October 31, 2010, 09:38:07 amThe MOV stayed at room temperature. I was checking it with an IR therometer. The MOV is good for 1 watt.You guess good, 1/4 watt. It survived the 130V. The 155V finished it off. It reads 9.7 Mega-ohms now.I have a 130V MOV to play with also. I need to calculate the watts this time for sure. First I am going to see if I can generate some switching transients and try to see the difference with & without the 14V MOV. Maybe a light switch & capacitor ? At the the 14V level.It will be Tuesday before I can do this. Going to the mountains tomorrrow for the day. Looking for fall folage.Thanks !

author: Simon
author_rank: Unknown
timestamp: November 01, 2010, 09:10:38 am
content: to make spikes turn a large fan on and off or other inductive load, i got 400V spikes out of a 24V system once. The vendor should not be charging you extra for testing, if his products have suddenly gone bad that is his problem not yours

author: TechGuy
author_rank: Regular Contributor
timestamp: November 02, 2010, 01:16:44 am
content: I would recommend checking the devices with failed MOVs for high voltage spikes (without the MOVs connected). If your device has a coil in it (inductor, motor, smps transformer) it could be causing excessive voltage spikes. The MOV will suppress the spikes for a period, but MOVs are perishable devices. Every time a MOV clamps a voltage spike it will degrade, to the point it completely fails. MOVs are nothing more than a Zinc Oxide semiconductor that transistions from a high impediance state to a low impledance state when encounters a high voltage pulse. Over time the zinc oxide will break down, usually in a state of low impediance. If this is indeed the case, then you will need to alter the device to including snubbers to attenuate the voltage spikes so that they don't trip the MOVs. You may wish to to include a small snubber in your design to clamp small line spikes in your device to extend the life of your MOVs. a small RC snubber will cull all of the lower power spikes so the MOVs don't have to trigger everytime something with a motor turns on (ie refig, HVAC, etc).QuoteRemember that 120 VAC is RMS voltage not peak voltage. 120VAC real peak voltage is 170V! (1.414*120V = 170V) A 130V MOV will burn out if you connecting to AC mains. A proper voltage rating for an AC Mains MOV is 180V.QuoteNot a lot of room to handle a moderate spike. You need at some kind of current choke such as an air core inductor to slew the spike, otherwise your MOV is a Wiley E Coyote with a lit stick of dynamite. I would recommend using a more robust MOV something in the 100J to 200 J range.FWIW, I recommend avoid using MOVs in high reliable devices since they are perishable devices. TVS diodes in the correct places provide a reliable way to clamp TVS events since the do not degrade.A TVS diode and a PTC fuse makes a good combo. The TVS diode clamps the spike the current inrush forces the PTC fuse into a high-impediance state attentuating the current flow to protect the TVS diode. For high power application I use a set of Air core Inductors, TVS diodes coupled with a Cap. A secondary Crowbar circuit with a higher TVS clamping voltage provides secondary defense. The first line of defense is the TVS diode Cap combo, which clamps small to moderate spikes.The Air core inductor serves as a choke to slow the change of current flow to avoid blowing the TVS diode. An air core inductor is more desirable because it will not saturate and you don't need a very large inductance. If the cap becomes fully charged, the input voltage will rise and trip the secondary crowbar circuit to clamp any all voltage. However when the crowbar trips, it usually blows the fuse as an SCR used in a crowbar circuit will not shut off until the voltage drops to zero. So its undesirable to make the crowbar circuit as your first line of defense.

author: SG-1
author_rank: Regular Contributor
timestamp: November 02, 2010, 05:49:16 am
content: Quote from: TechGuy on November 02, 2010, 01:16:44 amHere is the device. The MOV is supposed to protect two diodes & a capacitor.http://www.electromagnetic.biz/Portals/0/Docs/CDT/CTD1%20&%202%20UL.pdfHere is the data sheet for the 130V MOV. The maxium continous voltage is given in RMS. Or am I reading this incorrectly ??http://www.alliedelec.com/Images/Products/Datasheets/BM/LITTELFUSE/846-0244.PDFThe manufacturer is using a .6 watt (continuous )I have sent an e-mail to the manufacturer asking, why not a transil ??I will pass along your recomendation for not using the MOV in a high reliability devices, that they degrade every time they clamp.Thanks

author: SG-1
author_rank: Regular Contributor
timestamp: November 02, 2010, 05:55:26 am
content: Quote from: Simon on November 01, 2010, 09:10:38 amI agree with your premise, but if his device goes bad in our product, the customer will blame us. We will pay the warrenty cost to replace each unit. This is like the switch in your car that controls the window going up & down. The car manufacturer did not make the switch, but if it dies under warrenty he replaces it at his expence.

author: Simon
author_rank: Unknown
timestamp: November 02, 2010, 09:00:03 am
content: you should be passing onto your supplier any costs you incur in fixing the issue, if they sell you faulty gear and it causes £££ of damage that is theirs to pay for

author: FreeThinker
author_rank: Frequent Contributor
timestamp: November 02, 2010, 12:08:28 pm
content: Just my 2 cents but have you checked the mains supply?.High voltage harmonics may be a possible cause.

author: PetrosA
author_rank: Frequent Contributor
timestamp: November 02, 2010, 12:21:08 pm
content: I'm with FreeThinker on this. I think some power quality analysis is in order at point of use on one or more of the customer sites who have had your product fail. At minimum, I would want to see some data logs for voltage, even better, a fuller analysis with harmonics shown. At the least, this will show whether the component is being exposed to conditions outside its rating or not and if not, will go far in proving that it's a problem with the component itself.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: November 02, 2010, 12:39:49 pm
content: <snip from wikipeadia>While a MOV is designed to conduct significant power for very short durations (? 8/20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. Under normal utility voltage conditions, this is not a problem. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system.<snip>The neutral conductor in modern times cannot be relied on to remain at 0 volts WRT earth.This can cause significant voltage fluctuations for short periods of time causing havoc with voltage sensitive devices, and it's getting worse! see thread in this forumhttps://www.eevblog.com/forum/index.php?topic=1561.0

author: TechGuy
author_rank: Regular Contributor
timestamp: November 02, 2010, 08:10:51 pm
content: Quote from: SG-1 on November 02, 2010, 05:49:16 amOK Looks like its the correct MOV for AC power, I just wasn't sure from your earlier posts. A lot of folks forget to factor in the RMS voltage issue so I thought it was prudent to bring up.Is there a line filter in front of the surge suppressor (CTD-1 module)? A line filter includes a small RC filter to snub small spikes and to filter out common-mode noise.What is the device your protecting? Note from the CTD-1 module data sheet the intended application:QuoteThis device is using a half wave rectifier, and not a full bridge rectifer used in most devices. a half wave recifier will have issues with high current applications.Also note, this is a single channel shunt mode protector. It will not prevent damage from common mode surges, or other surge protectors that use three way surge protection. Consider if there is a common mode surge where line and neutral experience a common mode spike (ie both line and neutral have a 400V spike at the same time). Since the device has a earth ground, the MOV will do nothing and permit a high voltage differential between L-N and ground. The device will like pass the surge through it using the ground line.Consider that other devices at the customer premises might include a three way shutmode suppresion circuit that diverts the surge to ground. Now the high side of the surge is the Earth ground and use Line-Neutral and return blowing your device from the ground. Consider that the average household\commerical ground line has about 6 ohms resistance, providing ample room for destruction.Three way MOV surge protection:

author: SG-1
author_rank: Regular Contributor
timestamp: November 03, 2010, 02:28:10 am
content: Quote from: Simon on November 02, 2010, 09:00:03 amIn a corporation there is always a lot of politics & you have to watch out that somebodys relative is not involved. The decision to stay with this vendor will come from several layers up from me. Trying to collect would be difficult, because the cause of the failures will probably never be known. We say it's them, they say it is us. In the end the lawyers get it all anyway.

author: SG-1
author_rank: Regular Contributor
timestamp: November 03, 2010, 02:44:09 am
content: Quote from: FreeThinker on November 02, 2010, 12:08:28 pmThis is always a possibility. In which case the replacements will fail too. There is always a lot of other electronic devices present. The big dollar items are the protective relays. They can cost tens of thousands of dollars each. Usually customers do not place harmonic generating loads on the transformer for the switchgear control power. Most of these MOVs have failed inside the factory & in different ways. Some died on power up, others worked for a while. ( I remember one site with bad harmonics, they were burning up 3-Phase 75KVA CPTs. )

author: SG-1
author_rank: Regular Contributor
timestamp: November 03, 2010, 03:13:16 am
content: Quote from: FreeThinker on November 02, 2010, 12:39:49 pmIf this were the case a lot of more expensive equipment would be smoking on the primary & secondary side. This device is designed to operate continuously at 140VAC. The failures inside the factory have occured with multiple testers at different test stations. If other devices were failing for unknown reasons power quality could be examined. Much of the gear we supply has power quality instruments built in. You do bring up a good point and that is a great thread.

author: SG-1
author_rank: Regular Contributor
timestamp: November 03, 2010, 04:15:19 am
content: Is there a line filter in front of the surge suppressor (CTD-1 module)? A line filter includes a small RC filter to snub small spikes and to filter out common-mode noise.What is the device your protecting? Note from the CTD-1 module data sheet the intended application:QuoteThis device is using a half wave rectifier, and not a full bridge rectifer used in most devices. a half wave recifier will have issues with high current applications.Also note, this is a single channel shunt mode protector. It will not prevent damage from common mode surges, or other surge protectors that use three way surge protection. Consider if there is a common mode surge where line and neutral experience a common mode spike (ie both line and neutral have a 400V spike at the same time). Since the device has a earth ground, the MOV will do nothing and permit a high voltage differential between L-N and ground. The device will like pass the surge through it using the ground line.Consider that other devices at the customer premises might include a three way shutmode suppresion circuit that diverts the surge to ground. Now the high side of the surge is the Earth ground and use Line-Neutral and return blowing your device from the ground. Consider that the average household\commerical ground line has about 6 ohms resistance, providing ample room for destruction.Three way MOV surge protection:There is no line filter ahead of this or any other device on the AC supply. The AC supply typically consists of a stepdown Control Power Transformer. It's primary side is connected to the switchgear's medium voltage bus ( 2400-38000 volts ), usually Line to Line. The secondary side is wired for 240/120. The gear is a giant steel box with a .25x2 inch ground bus traveling through. The ground references are attached to the ground bus. Resistance would be very low. There are other devices present that are much more sophisticated, the protective relays like the SEL brand. The CTD-2 does not have a ground reference. The relays do. Some relays have a chassis ground, safety ground, & a filter ground.The device we are protecting varies greatly. Medium Voltage Switchgear is used as service entrance equipment for hospitals, large industral plants, etc.The devices all utilize the primary voltage, say 13800. Lets say the load is a 12,000 HP air compressor. That section of gear would provide a protective relay ( customer's choice ) for the motor. The protective relay senses a problem has developed, maybe high temperature on a set of bearings. The relay then closes a normally open contact. This completes a trip circuit for the medium voltage circuit breaker, the CTD-2 supplies the DC voltage. Customers that are too cheep to maintain a battery rack use a capacitor trip device. Maybe they just think it is more "green". The trip current is 6 amperes peak. The shunt trip coil is energized for 34 milli-seconds. With the AC control off, the CTD-2 capacitor is discharged from 179VDC to 80VDC.What do you consider a high current application ? For our switchgear that would be about 4000 amperes.

author: PetrosA
author_rank: Frequent Contributor
timestamp: November 03, 2010, 05:52:15 am
content: I think that last post put things into scale for me. I can see how having a 12,000 HP motor shutting off unnecessarily would be a problem. I also see that recommending you look for answers over on mikeholt would be useless(I thought your nick looked familiar...) Good luck with getting a solution!

author: TechGuy
author_rank: Regular Contributor
timestamp: November 03, 2010, 04:51:11 pm
content: QuoteSounds like the CTD-2 is being used for its intended application as a power source for a trip breaker. I though perhaps the CTD-2 was being used for to supply rectified DC power for an applicance.Based upon your information, I suspect the problem may be line noise caused by the AC motors, or even the switchgear. I would ask the vendor of the CTD-2 if they have problems with there device at sites that have industrial equipement creating a lot of spikes caused by large AC Motors (induction leakage spikes). Ask them if including a line filter or an RC snubber to attenuate the spikes would solve the problem or if they have a better solution. I suspect the line filter would correct the problem but I can't guarentee it. An AC line monitor test would required to make sure the Line filter was properly attenuating the noise.That said, I wonder if the MOV is really necessary, since if I understand the application, the CTD-2 is a reserve power supply to trip a relay or breaker during a power loss. Relays and breakers are not senstitive to power surges, unless they contain semicondutors. Most relays and breakers contain no semiconductors.

author: SG-1
author_rank: Regular Contributor
timestamp: November 04, 2010, 12:10:04 am
content: Quote from: PetrosA on November 03, 2010, 05:52:15 amIn this instance it would not be able to shut down for any reason, by the time somebody used their finger to open the breaker all the magic smoke would be out of the million dollar+ motor. Fire Dept in route. Lawers right behind. All because of a MOV failure. Now imagine this is a main breaker for a hospital.See you over at Mikes. Don't tell them I have been whoreing around !!I have been communicating with GAR.

author: SG-1
author_rank: Regular Contributor
timestamp: November 04, 2010, 03:56:38 am
content: Quote from: TechGuy on November 03, 2010, 04:51:11 pmHad an engineer try to use a cap trip device for a power supply once, I was in warrenty then. Customer called said cap trip had failed. Air express a new unit, not the CTD-2. Six months later he calls back with the same complaint. The prints are pulled for his order & he get a real power supply this time. Engineer gets promotion.The vendor says we are the only customer having a problem.The power circuit breaker that would require a capacitor trip has a full wave bridge rectifier in it's closing circuit ( it is built into the breaker ). I think that recitifier is a 400 volt, 20A model. The closing coil & the trip coil only come in DC. The breakers weigh between 250 & 1900 pounds.http://www.eaton.com/EatonCom/Markets/Electrical/Products/CircuitProtection/MediumVoltagePowerBreakers/index.htmThe square ones are 36 inches wide.They have a universal type motor to charge the springs. Basically a drill motor. Potential spike generator. We have been using the CTD-2 for years with no problems, then last month... The vendor claims the MOV is there to protect the 250V capacitor as spikes will charge it above the usual 169 volts. If that is the case I think he has chosen the wrong device.The relays are protective relays, that run complex algorithims to analyze the wave forms from the current transformers & potential transformers. They serve as the brains where as the breaker is the brawn. I am sure their input protection is more soficsophisticated than the CTD-2. These devices sell for 10s of thousands of dollars.http://www.selinc.com/products/

author: SG-1
author_rank: Regular Contributor
timestamp: November 04, 2010, 04:10:04 am
content: 130V MOV ResultsAll readings are in Volts AC RMS.I changed the 10K 1/4 watt resistor to a 4K 12 watt wire wound resistor.The 1 watt MOV did get slightly warm to the touch. The voltage was only on long enough to capture the data.INPUT VOLTAGE MOV VOLTAGE129 129134 134139 139144 143154 150170 159180 164200 171225 177250 182

author: Zero999
author_rank: Super Contributor
timestamp: November 06, 2010, 08:14:40 pm
content: I assume you tested it with AC voltage?If so, did you use a true sine wave meter?If not the results could be distorted.An oscilloscope is the best way to test this but you'll need to run it off an isolation transformer for safety reasons.

author: SG-1
author_rank: Regular Contributor
timestamp: November 06, 2010, 09:46:48 pm
content: As stated the voltages are in AC RMS. I used a Fluke 196C. I am just too blonde to post the pictures. I have found additional options, browse, I selected a j-peg, the location appeared in the attach box. I do not see how to upload it. When I click on preview it does not appear in the preview only the text.

author: SG-1
author_rank: Regular Contributor
timestamp: November 07, 2010, 01:02:08 am
content: Lets try some more. Blue is the input voltage & red is the MOV voltage. This is the 130V MOV. I used a point & shoot camera to "capture" the screen.

author: SG-1
author_rank: Regular Contributor
timestamp: November 07, 2010, 01:10:11 am
content: The RMS values themselves are deceiving. The MOV is holding the peak to about 200 volts & the wave is getting flatter with each increase in voltage.

author: SG-1
author_rank: Regular Contributor
timestamp: November 07, 2010, 02:10:57 am
content: Some new numbers that make more sense. It also seems to make more sense that if you are trying to protect a device from transients, that you actually want to protect it from the peak value, because the RMS wave form may be distorted, as it clearly is here.

author: Zero999
author_rank: Super Contributor
timestamp: November 07, 2010, 08:49:51 am
content: Quote from: SG-1 on November 07, 2010, 01:10:11 amYes, that makes sense.As you can see, the RMS voltage will be equal to the input voltage, until it starts clipping, then the RMS voltage will rise towards the limit of the clipping voltage (200V) but will never actually reach it. The maximum AC voltage you can connect to the MOV is 141VAC but to avoid clipping during normal operating in the nominal maximum operating voltage should be around 10% under the clipping voltage so that's 127V.

author: SG-1
author_rank: Regular Contributor
timestamp: January 10, 2011, 03:16:27 am
content: UPDATE:First thanks to everyone who helped by replying.The manufacture has change the MOV from a 150 volt to a 175V model. They have also increased the test voltage from 120 to 150VAC for 6 hours of the 24 hour burn in. Other tests, such as the capacitor discharge time, are also performed. And like the man falling off the 100 story building & is passing the 50th floor, so far so good !

author: Zero999
author_rank: Super Contributor
timestamp: January 11, 2011, 07:04:22 pm
content: Well it looks like the voltage rating is the peak voltage which is odd for AC MOVs which are normally spevified at the RMS operating voltage,Anyway, I'm glad it seems to be working.

author: saturation
author_rank: Super Contributor
timestamp: January 11, 2011, 08:37:42 pm
content: Same here, and appreciate SG-1 for posting the photos.Quote from: Hero999 on January 11, 2011, 07:04:22 pm