# VFD electrical problem - MOV Varistor



## oliquir (Jan 13, 2011)

vfd is dead, probably had an overvoltage and some chips inside have blown. Just buy another one.


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## kostas (Sep 15, 2014)

oliquir said:


> vfd is dead, probably had an overvoltage and some chips inside have blown. Just buy another one.


I am not sure if it is dead since, it keeps working even with this blown varistor.
What if I use a ups with stable voltage?


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## triden (Jun 13, 2012)

It'll work without the varistor, bit the next surge will take out your whole PCB. Do not run the drive with a blown MOV.


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## JRaef (Mar 23, 2009)

That drive is one of the worst POS designs on the market, it's no surprise that an MOV failed. The next failure is forthcoming, regardless of whether or not you replace that MOV. 

Most likely if it is still running, it's because that is one of the MOVs used to protect the line side converter components from spikes and faults on the incoming AC line. If I had to guess, I'd say that you connected to an AC input that was not referenced to ground or has a high resistance ground, so your MOVs were supposed to have their ground reference removed, but the crap manual did not explain that to you in an understandable way, or was ignored because the Chinese have no clue as to ungrounded systems in North America. The first ground fault ANYWHERE on that line then attempts to find ground through those MOVs, they do their job, but only once because it fries them. Every subsequent spike or ground fault is causing incremental damage to the rest of the components in the entire drive. If you are I distant on continuing to use this, any MOV rated for 2.5x your line voltage will work.


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## Jhellwig (Jun 18, 2014)

If it shoots sparks it is done for.

Even a high dollar Allen Bradley inverter is a throw away when they die that hard.


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## John Valdes (May 17, 2007)

Jhellwig said:


> If it shoots sparks it is done for.
> Even a high dollar Allen Bradley inverter is a throw away when they die that hard.


I am curious as to your name. Are you into DC motors or do you work for Hellwig?


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## Jabberwoky (Sep 2, 2012)

Jhellwig said:


> If it shoots sparks it is done for.
> 
> Even a high dollar Allen Bradley inverter is a throw away when they die that hard.


I would say that is not always the case. I have done complete restorations of drives with engulfing cabinet fires. I would get some quotes before throwing away any high value drives. Any legitimate repair facility can usually tell you in a few hours if it will be cost effective.


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## kostas (Sep 15, 2014)

JRaef said:


> That drive is one of the worst POS designs on the market, it's no surprise that an MOV failed. The next failure is forthcoming, regardless of whether or not you replace that MOV.
> 
> Most likely if it is still running, it's because that is one of the MOVs used to protect the line side converter components from spikes and faults on the incoming AC line. If I had to guess, I'd say that you connected to an AC input that was not referenced to ground or has a high resistance ground, so your MOVs were supposed to have their ground reference removed, but the crap manual did not explain that to you in an understandable way, or was ignored because the Chinese have no clue as to ungrounded systems in North America. The first ground fault ANYWHERE on that line then attempts to find ground through those MOVs, they do their job, but only once because it fries them. Every subsequent spike or ground fault is causing incremental damage to the rest of the components in the entire drive. If you are I distant on continuing to use this, any MOV rated for 2.5x your line voltage will work.


Ok, please let me explain the wiring from vfd and spindle. Please ignore the red letters on the attached image.

I wired the line plug to the R,T and the line ground to the ground terminal (which is next to W terminal).The U,V and W have been wired to the 3 of the 4 pins of my 2.2kw, spindle, while the 4th pin is unpluged. Now, I am not sure if the grounding is ok, but I need to inform you that when I am doing the Z touching probe to find the Z of the material, I attach the first probe to the pcb that is on the material and the other probe is attached to the spindle mount bracket that holds the spindle. This way I can get a closed circuit when my end mill bit touches the pcb. Is this an indication of a bad grounding from vfd and spindle?

Thanks.


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## Jhellwig (Jun 18, 2014)

Jabberwoky said:


> I would say that is not always the case. I have done complete restorations of drives with engulfing cabinet fires. I would get some quotes before throwing away any high value drives. Any legitimate repair facility can usually tell you in a few hours if it will be cost effective.


Allen Bradley had a slug of badly made powerflex 700s that we were getting. It was cheaper to junk them than have almost everything replaced in them. It wasn't all the drives fault but the toshiba drives were holding up way better. I had several times where I would change 3 to 4 drives a day.

The place that was rebuilding them was doing a crappy job also. It was a 50/50 chance if a rebuilt drive would work. Add that to the cost of rebuilding and it was better that most if them got junked.

I do realize though that that plant was not a typical place and a lot of it was the environment and management practices. These cheapie drives nowadays are getting to be a throw away design.


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## Jhellwig (Jun 18, 2014)

John Valdes said:


> I am curious as to your name. Are you into DC motors or do you work for Hellwig?


My last name is Hellwig. No relation to any company though.


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## sparkywannabee (Jan 29, 2013)

Jhellwig said:


> Allen Bradley had a slug of badly made powerflex 700s that we were getting. It was cheaper to junk them than have almost everything replaced in them. It wasn't all the drives fault but the toshiba drives were holding up way better. I had several times where I would change 3 to 4 drives a day.
> 
> The place that was rebuilding them was doing a crappy job also. It was a 50/50 chance if a rebuilt drive would work. Add that to the cost of rebuilding and it was better that most if them got junked.
> 
> I do realize though that that plant was not a typical place and a lot of it was the environment and management practices. These cheapie drives nowadays are getting to be a throw away design.


This issue must have been isolated to powerflex drives, in my experience AB is the only way to go, accept no substitute. Last place i worked at for 21 yrs, we had a couple of 1336 vectorless run 24/7 for 15 yrs, no issues. Also had 150hp-250p 1395 DC drives run 24/7 for over a decade, no issues. Upgraded to Controllogix from Automax in 08, no issues. I think there was a micrologix 1500 I had to load the program couple of times over the years. Siemens drives I had to get in so much that I had damn parameters memorized.BTW, it was a bad environment, lots of paper dust, ink mist etc.


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## Zana (Jul 25, 2014)

I wouldn't run a drive with a bad MOV Varistor. Might as well junk it and replace it, because it's going to junk itself eventually.


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## sulfur (Mar 2, 2015)

*Exploding Powerflex 753's*

Our plant has had seven PF753's explode in the last year. Powerflex 400's in same environment have done fine. Anyone else seen these drives explode randomly? One even exploded while it was not running, just powered on. All have been 50-60HP range. Ethernet cards are showing corrosion on gold plated copper connectors, but that does not seem to be the source of them exploding, same type of connectors on main board, do not show corrosion, oddly enough. Explosion blows the cover right off. I can post pictures of not sure where to put them, site does not seem to allow upload?






JRaef said:


> That drive is one of the worst POS designs on the market, it's no surprise that an MOV failed. The next failure is forthcoming, regardless of whether or not you replace that MOV.
> 
> Most likely if it is still running, it's because that is one of the MOVs used to protect the line side converter components from spikes and faults on the incoming AC line. If I had to guess, I'd say that you connected to an AC input that was not referenced to ground or has a high resistance ground, so your MOVs were supposed to have their ground reference removed, but the crap manual did not explain that to you in an understandable way, or was ignored because the Chinese have no clue as to ungrounded systems in North America. The first ground fault ANYWHERE on that line then attempts to find ground through those MOVs, they do their job, but only once because it fries them. Every subsequent spike or ground fault is causing incremental damage to the rest of the components in the entire drive. If you are I distant on continuing to use this, any MOV rated for 2.5x your line voltage will work.


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## JRaef (Mar 23, 2009)

sulfur said:


> Our plant has had seven PF753's explode in the last year. Powerflex 400's in same environment have done fine. Anyone else seen these drives explode randomly? One even exploded while it was not running, just powered on. All have been 50-60HP range. Ethernet cards are showing corrosion on gold plated copper connectors, but that does not seem to be the source of them exploding, same type of connectors on main board, do not show corrosion, oddly enough. Explosion blows the cover right off. I can post pictures of not sure where to put them, site does not seem to allow upload?


The only thing inside of the drive capable of creating enough force to "blow the covers off" is if the capacitors are exploding. That is usually caused by one of two things: Excessive voltage on the caps or freezing. Being that it's winter, any chance the VFDs were exposed to extreme cold?

By the way re; pictures. You cannot post directly into the thread here, but you can post your pics to another picture hosing site, like Photobucket.com (they're free), then you will be able to copy a link to that photo and paste the link into the "Insert image" option in a posting here. The software for this forum will go fetch the image and display it in your response.


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## macmikeman (Jan 23, 2007)

JRaef said:


> By the way re; pictures. You cannot post directly into the thread here, but you can post your pics to another picture hosing site, like Photobucket.com (they're free), then you will be able to copy a link to that photo and paste the link into the "Insert image" option in a posting here. The software for this forum will go fetch the image and display it in your response.



Psssst, Secret..... This place is a photo hosting site. Just make a dozen or two photo albums in your user control panel, like how I do, and then copy the link to them. That way you don't have to join any other site and give them your info, Cause they bad, and Cricket good......


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## KennyW (Aug 31, 2013)

Jhellwig said:


> Allen Bradley had a slug of badly made powerflex 700s that we were getting. It was cheaper to junk them than have almost everything replaced in them. It wasn't all the drives fault but the toshiba drives were holding up way better. I had several times where I would change 3 to 4 drives a day.
> 
> The place that was rebuilding them was doing a crappy job also. It was a 50/50 chance if a rebuilt drive would work. Add that to the cost of rebuilding and it was better that most if them got junked.
> 
> I do realize though that that plant was not a typical place and a lot of it was the environment and management practices. These cheapie drives nowadays are getting to be a throw away design.


Rockwells approach to input movs and common mode capacitors has never made any sense to me. Like all rockwell guys I have seen so many blown up drives becuase of this its not funny. 

They will maintain that they "need" to sell them that way, but then make the default setting for the retention of thermal overload memory set to "off" even though retaining thermal on power off is a code requirement. 

Strange an inconsistent engineering decisions. Well, unless you call the fact that in both cases the default setting is the one most likely to result in equipment damage consistent...


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## Jhellwig (Jun 18, 2014)

Allen Bradley have a ground jumper to the movs. It has to be removed on anything other than a solidly grounded wye system otherwise when a surge occurs the inverter is the ground reference and it will blow up the drive. That is examined right in the instructions.

Another thing I know of with the Allen Bradley powerflex 700s is the electronics do not have a conformal coating to protect them from corrosion. It got made into a option after corrosion was eating them up. I don't know if it is standard on the newer series of drives or not.


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## JRaef (Mar 23, 2009)

Jhellwig said:


> Allen Bradley have a ground jumper to the movs. It has to be removed on anything other than a solidly grounded wye system otherwise when a surge occurs the inverter is the ground reference and it will blow up the drive. That is examined right in the instructions.
> 
> Another thing I know of with the Allen Bradley powerflex 700s is the electronics do not have a conformal coating to protect them from corrosion. It got made into a option after corrosion was eating them up. I don't know if it is standard on the newer series of drives or not.


It did used to be an option, it is now standard on all drives, old or new series alike. they implemented that decision in 2011.


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## KennyW (Aug 31, 2013)

Yes there used to be an "EMC Option". If you selected that option it meant there was a 50% chance they'd remember to leave the jumpers out. :jester:

My point was more that it's silly that they ship them with emc compliance by default yet the default parameter for overload retention doesn't even meet the NEC. 

I know items are documented but the default options seems backwards. 

It should say "if you need emc compliance, jumpers must be installed. WARNING do not install jumpers on resistance grounded or ungrounded networks". 

At least that way the worst case if you drive makes noise you will probably never notice, and if you do notice, you'll search for the tech note and put the jumpers in. The way it is now, you search for the tech note after the drive EXPLODES. Lame. 

Same for overload retention. It should say "Drive thermal overload memory is retained when the drive is de-energized as is require per NEC. If the ability to reset thermal memory via a power cycle is required for emergency service you must alter parameter xxx". 

Just kinda bizarre yet easily remedied. When I start up an ACS800 I enter motor nameplate and a couple other things.

When I start up a PF7xx I go through a zillion parameters based on if it has an output filter, etc etc. that need to be set up otherwise you never know what might happen.


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## JRaef (Mar 23, 2009)

KennyW said:


> Rockwells approach to input movs and common mode capacitors has never made any sense to me. Like all rockwell guys I have seen so many blown up drives becuase of this its not funny.
> 
> They will maintain that they "need" to sell them that way, but then make the default setting for the retention of thermal overload memory set to "off" even though retaining thermal on power off is a code requirement.
> 
> Strange an inconsistent engineering decisions. Well, unless you call the fact that in both cases the default setting is the one most likely to result in equipment damage consistent...


All drives have the same issue, Rockwell just does a better job of making it clear and easy to deal with. Some drives get really complicated and don't make it clear for US customers. Here's an example of how ABB words it:



> Unsymmetrically grounded networks are defined in the following table.... In such networks, the internal connection provided by the EM3 screw (on frame sizes R1…R4 only) must be disconnected by removing EM3. If the grounding configuration of the network is unknown, remove EM3.
> Note: ACH550-UH drives are shipped with the screw removed (but included in the conduit box).
> 
> For floating networks (also known as IT, ungrounded, or impedance/resistance grounded networks):
> ...


When I worked for ABB, I would say that 99.9% of customers had no idea what this was saying, "Unsymmetrically grounded networks" or "IT network" means nothing to us here in North America, and the word "network" makes electricians immediately think this has to do with communications, so it doesn't apply. 

Siemens was even worse, at least ABB gave you simple screws to remove. Siemens makes you disassemble the front-end of the drive, find and clip a ground strap, then cap it, then reassemble the front-end. 

Most Asian drives make no mention of it at all, other than to say, somewhere in the bowells of their tech support system, that "These drives are designed for use in T-N networks..." (words from Yaskawa, but the others are similar), with no mention of it being UNsuitable for ungrounded systems or what to do about it. Again, what does "T-N network" mean to us here? So most people never pay attention, the drives fry and they think it was their fault.



> ...even though retaining thermal on power off is a code requirement.


You must be referring to 430.126. The tricky part of that is that the requirement for retentive thermal memory is only related to having a system that tracks motor temperature AND SPEED together. You can ALSO just supply a motor thermal overload protector meeting the requirements of 430.32. Since 2005, all VFDs that are UL listed must now ALSO be listed as a thermal OL relay at the bare minimum, i.e. 430.32. So yes, you CAN enable the retentive thermal tracking system and use it, but if you do not, then it STILL provides basic thermal overload protection satisfying 430.32 as a minimum, which is one of the options in 430.126. Funky? Yes. But remember, it wasn't a requirement until 2005, so all existing systems up to that point didn't have it, and making a unilateral change in default programming can cause massive headaches. So they left it as optional, with the default being just the basic OL protection.


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## KennyW (Aug 31, 2013)

JRaef said:


> All drives have the same issue, Rockwell just does a better job of making it clear and easy to deal with. Some drives get really complicated and don't make it clear for US customers. Here's an example of how ABB words it:


You did not quite get my meaning. I realize that any drive shipped with EMC filtering will have the same problem. What I don't agree with is the policy of shipping drives with that filtering as a default. I also know this practice is not limited to Rockwell. That said, this policy is also not universal, and IMO companies that only apply emc filtering as an option code are doing a good thing. If a person is smart enough to determine they need it (and also the description of the option code usually states solidly grounded right in it), chances are they won't accidentally misapply it. 





> You must be referring to 430.126. The tricky part of that is that the requirement for retentive thermal memory is only related to having a system that tracks motor temperature AND SPEED together. You can ALSO just supply a motor thermal overload protector meeting the requirements of 430.32. Since 2005, all VFDs that are UL listed must now ALSO be listed as a thermal OL relay at the bare minimum, i.e. 430.32. So yes, you CAN enable the retentive thermal tracking system and use it, but if you do not, then it STILL provides basic thermal overload protection satisfying 430.32 as a minimum, which is one of the options in 430.126. Funky? Yes. But remember, it wasn't a requirement until 2005, so all existing systems up to that point didn't have it, and making a unilateral change in default programming can cause massive headaches. So they left it as optional, with the default being just the basic OL protection.


A couple points then: 

1) Unilateral changes in default programming are common place, by Rockwell and by all manufacturers. Plenty of major revision releases have gone out with much more drastic changes than that. Yay for release notes, right? What do you propose would have happened if this default had been changed when the 2005 NEC came out? 

2) This is also default on PF75x drives, which I am pretty sure are post 2005? 

3) When an impatient electrician gets a drive fault that won't reset (like an overload that is waiting for the thermal to count back down), and operations is on his back to reset the fault and get production running, guess what he does? 

He cycles the power to the drive. 

This is the normal state of affairs on site and normal human nature. Yes you can say that electrician should have training and know better. Fine, I won't argue, but my personal design philosophy does not agree, taking human nature into account is important. So again not saying they are wrong, but just like the above, in my opinion as a default setting, not retaining it is a poor choice. And again I know rockwell is not the only one (Schneider for sure work this way as well). Sorry I didn't mean to particularly single Rockwell out. 

I have seen several motors get nuked over the years thanks to this one (the conveyor has a mechanical issue, overload trips, and they keep resetting the drive and trying to start it, the drive is oversized and sized based on HD rating so the motor fries before the drive itself overheats). Now when I start up a drive I always make sure I set it. IMO it is a bit crazy that needs to be done. Same goes for the settings related to output filtering. 


Sorry I didn't mean to come across as anti-rockwell, they do a lot of things well.

Also I think maybe high resistance grounding on 480 and 600v transformers is more common in Canada than in the US, so the jumper thing affects us more?


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## ibew415 (Mar 23, 2014)

JRaef said:


> The only thing inside of the drive capable of creating enough force to "blow the covers off" is if the capacitors are exploding. That is usually caused by one of two things: Excessive voltage on the caps or freezing. Being that it's winter, any chance the VFDs were exposed to extreme cold?
> 
> By the way re; pictures. You cannot post directly into the thread here, but you can post your pics to another picture hosing site, like Photobucket.com (they're free), then you will be able to copy a link to that photo and paste the link into the "Insert image" option in a posting here. The software for this forum will go fetch the image and display it in your response.


Is this an issue with oil filled capacitors? film? 

I imagine all VFDs need to be kept from a freezing enviroment.
I have been telling the plant manager at the quarry i work at to get the heat fixed in the electrical rooms because the cold is not good for the drives.

They will run a VFD that is 5 degrees F...and not blink an eye.


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## JRaef (Mar 23, 2009)

ibew415 said:


> Is this an issue with oil filled capacitors? film?
> 
> I imagine all VFDs need to be kept from a freezing environment.
> I have been telling the plant manager at the quarry i work at to get the heat fixed in the electrical rooms because the cold is not good for the drives.
> ...


Not oil filled, but electrolytic capacitors will freeze. The electrolyte is typically a water based gel, but there are several different kinds used, so the freezing properties differ. The problem is, there is no way to tell which one you have and what the freezing temperature is for it.


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## NC Plc (Mar 24, 2014)

JRaef said:


> Not oil filled, but electrolytic capacitors will freeze. The electrolyte is typically a water based gel, but there are several different kinds used, so the freezing properties differ. The problem is, there is no way to tell which one you have and what the freezing temperature is for it.


Is this part of the reason as to why PLCs and other electrical devices stop working in the cold? I had to install three 550w space heaters to keep them running in the winter.

Another question is I am installing a small VFD and an electrical enclosure soon and I am wondering how cold is too cold for it. Do VFDs have issues when the temps get down to 20-30 degrees?


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## JRaef (Mar 23, 2009)

NC EET said:


> Is this part of the reason as to why PLCs and other electrical devices stop working in the cold? I had to install three 550w space heaters to keep them running in the winter.
> 
> Another question is I am installing a small VFD and an electrical enclosure soon and I am wondering how cold is too cold for it. Do VFDs have issues when the temps get down to 20-30 degrees?


The primary problem with cold is condensation. When you have electrical equipment, it's warm and when you turn it off, it cools down. When the warm metal surfaces, which are also the CONDUCTIVE surfaces in many cases, cool down to below the dew point, airborne water vapor condenses on it and starts shorting things out or causing corrosion.

30 degrees is probably OK, but 20 is getting down there. Most drives will have an OPERATING temperature limit of -10deg C, about 14deg F. At 20F, you are getting to the edge of acceptability of the surrounding air and if it stays there long enough with no power applied or dips below 20F for a lesser period, the caps can freeze.


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## NC Plc (Mar 24, 2014)

JRaef said:


> The primary problem with cold is condensation. When you have electrical equipment, it's warm and when you turn it off, it cools down. When the warm metal surfaces, which are also the CONDUCTIVE surfaces in many cases, cool down to below the dew point, airborne water vapor condenses on it and starts shorting things out or causing corrosion.
> 
> 30 degrees is probably OK, but 20 is getting down there. Most drives will have an OPERATING temperature limit of -10deg C, about 14deg F. At 20F, you are getting to the edge of acceptability of the surrounding air and if it stays there long enough with no power applied or dips below 20F for a lesser period, the caps can freeze.


So it might be worthwhile to put a space heater in there just to make sure it doesn't get too cold? A small little 550w one that will kick on if the temperature drops below say 35 or so.


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