# VFD post mortem



## gpop (May 14, 2018)

Most likely its been surged many times over the years or possibly had a motor crap out which has lead to a component failure. As its lasted 8 years past the point where the caps were rated to fail i wouldn't be looking to deep. 

I would test the motor before replacing the drive as a dead short could cause the new drive to instantly smoke. Looks fairly clean inside (no rust on screws) so i wouldn't expect moisture to be the cause.


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## micromind (Aug 11, 2007)

gpop said:


> I would test the motor before replacing the drive as a dead short could cause the new drive to instantly smoke. Looks fairly clean inside (no rust on screws) so i wouldn't expect moisture to be the cause.


I'll second this........no way would I install a new drive without testing the motor and its conductors first.


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## joe-nwt (Mar 28, 2019)

Motor was tested and new drive installed and running. Just looking for opinions on the damage. Thanks for the replies!


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## joe-nwt (Mar 28, 2019)

gpop said:


> Most likely its been surged many times over the years or possibly had a motor crap out which has lead to a component failure. *As its lasted 8 years past the point where the caps were rated to fail* i wouldn't be looking to deep.


While I was eating supper I was thinking about this. Is this a known thing? Is there a set interval where caps should be replaced? Is it based on starts, run hours or strictly age? 

If you have some info I'd sure like to hear it. That same customer has at least 7 more of the same drives all the same vintage. One other drive was replaced by me in 2011 but the rest are still running.


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## Navyguy (Mar 15, 2010)

I would suspect the clear spot on the board is where the failure happened and the melted solder joints are the failed component. Why it failed, can't tell for sure if it was a short on the solder side or a failure on the component side. I agree it looks pretty clean on the inside compared to many I have seen.

If there was a extreme small amount of some carbon dust, you have had some tracking... not sure the environment.

Cheers
John


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## varmit (Apr 19, 2009)

15 to 16 years is a great life span for a VFD. I usually figure about an 8 year life span. Sometimes they last longer,sometimes less.


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## EJPHI (May 7, 2008)

Some good advice here. When semiconductors blow up, you can suspect arcing, over-voltage, load misbehavior, logic/control malfunction, condensation, or heat. The effect of these stresses can cumulate until boom! Seems like 8 years is a good long time before failure. Was the drive operating 24/7? That would be almost 70k hours. Most electronic components have a very long life and failure rates are, of course, low. But if you put a whole bunch of these parts in a box statistically, the reliability drops quite a bit until you get something like 8-10 years of life for the whole assembly.

You say there are several of this same drive in the facility. Do they share any of the same supply wiring? 

Electrolytic capacitors are a special case. They dry out as they age and a good rule of thumb is to halve their MTBF for each 10C rise in temperature. The 2000 hour 85C rated capacitors are expected to fail after only 16000 hours at 55C. In my business, I see electrolytic capacitor failures after 10-20 years in instrumentation and like to put in 105-125C 5000 hour rated replacements. When these capacitors fail, their internal resistance goes up and they leak corrosive juices onto the circuit board. I'll probably do the same as I age out.


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## joe-nwt (Mar 28, 2019)

Navyguy said:


> I would suspect the clear spot on the board is where the failure happened and the melted solder joints are the failed component. Why it failed, can't tell for sure if it was a short on the solder side or a failure on the component side. I agree it looks pretty clean on the inside compared to many I have seen.
> 
> If there was a extreme small amount of some carbon dust, you have had some tracking... not sure the environment.
> 
> ...



The clear spot on the board had me looking as well. I found out after the fact there was an initial failure and a breaker was found tripped and then reset was attempted with another bang. I was wondering if the scorching and resultant carbon from the initial pop, and if the clear spot/melting wasn't from the second energizing. 

Also funny you mention fine carbon dust. This drive was in a containerized bio-mass boiler. There is fine carbon-ash inside the building, but the drive was in a control cabinet with filtered air system. There is still fine dust however, it's noticeable in places inside the cabinet.


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## joe-nwt (Mar 28, 2019)

EJPHI said:


> Some good advice here. When semiconductors blow up, you can suspect arcing, over-voltage, load misbehavior, logic/control malfunction, condensation, or heat. The effect of these stresses can cumulate until boom! Seems like 8 years is a good long time before failure. Was the drive operating 24/7? That would be almost 70k hours. Most electronic components have a very long life and failure rates are, of course, low. But if you put a whole bunch of these parts in a box statistically, the reliability drops quite a bit until you get something like 8-10 years of life for the whole assembly.
> 
> You say there are several of this same drive in the facility. Do they share any of the same supply wiring?
> 
> Electrolytic capacitors are a special case. They dry out as they age and a good rule of thumb is to halve their MTBF for each 10C rise in temperature. The 2000 hour 85C rated capacitors are expected to fail after only 16000 hours at 55C. In my business, I see electrolytic capacitor failures after 10-20 years in instrumentation and like to put in 105-125C 5000 hour rated replacements. When these capacitors fail, their internal resistance goes up and they leak corrosive juices onto the circuit board. I'll probably do the same as I age out.



Drive are in use for 24/7 for 6 months out of the year, off completely for the rest. Some drive in another facility, some in the same facility and some do share the same supply wiring. 

Although they are in the same container as the boiler, typically cold winter air is also coming into the container as combustion air so on average I don't think the ambient temperature would go much above say 30C, so I don't think this is a big factor in this particular case. 

Tomorrow I'm going to pry that heat sink off and see what was damaged underneath. If I see anything interesting I'll post a pic.

Thanks all.


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## gpop (May 14, 2018)

joe-nwt said:


> While I was eating supper I was thinking about this. Is this a known thing? Is there a set interval where caps should be replaced? Is it based on starts, run hours or strictly age?
> 
> If you have some info I'd sure like to hear it. That same customer has at least 7 more of the same drives all the same vintage. One other drive was replaced by me in 2011 but the rest are still running.



It was normal to replace the caps in the days when vfd were designed to be repaired and serviced on-site. Now most are disposable so you just run them to failure. 

While the drive is up the caps are in use so its based on time. Shutting the drive off to extend its life tends not to work as the pre-charge board seems to fails after hundreds of cycles.
( If you have a new drive that has not been powered up for a few years the caps may fail instantly or after a short period of time.) 
Each drive manufacturer will have a expected life cycle of so many hour in the manual but its ball park especially based on where the drive is mounted. Some of the drive i have worked on in cold room are over 25 years old and i believe the manual stated 90k hrs. Modern caps may have a longer life then the older caps and some of the newer drives can handle temperatures that would have killed a old style drive with in months. To be honest i don't bother reading a lot of the technical stuff in the manual any more as its going to be run to failure.

On some old drives you will start to see the affects of the caps failing before they die so you end up changing the drive before it totally fails because it gets annoying having them trip out on a sudden load change. 

I have seen at least 80 drives fail and a few of them completely blow up.(we had over 300 on-site). Yours is a minor pop as it seems to have contained the arc in the casing. I was not being condescending when i said you needed to test the motor as i have been on many a call out where the first drive blew then the second and on one call it was the forth (motor megged good shame he didn't test the wiring that was phase to phase). Places that use remote reset of drive (including turning it off and on) also like to nuke them as there to lazy to read the fault code.(ground fault reset to gamble on running or detonation, reset, reset, reset, boom) The operator will tell you how they have had to reset that drive every shift for weeks after its blow up. 

Power spikes also have a tendency to kill vfd's so make sure they have at least a main surge-suppressor in the mcc. One night a company next door had a lightning strike with no surge suppression and 7 vfd's split there caps and had oil running out of the buckets (they remote reset one and it went with a huge bang before they called for assistance)


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## gpop (May 14, 2018)

joe-nwt said:


> The clear spot on the board had me looking as well. I found out after the fact there was an initial failure and a breaker was found tripped and then reset was attempted with another bang. I was wondering if the scorching and resultant carbon from the initial pop, and if the clear spot/melting wasn't from the second energizing.


I have seen a 7.5 hp drive take out a 15amp, 200 amp, and the 800 main breaker and little bits of vfd flew all over the MCC. I tend to be a bit more paranoid now and insist on fuses before the drive. If i have to test a drive with a tripped breaker/blow fuses (more than one) i use 1-3 amp fuses as that's all that's required to get the drive up so i can see the fault log.


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## EJPHI (May 7, 2008)

joe-nwt said:


> Drive are in use for 24/7 for 6 months out of the year, off completely for the rest. Some drive in another facility, some in the same facility and some do share the same supply wiring.
> 
> Although they are in the same container as the boiler, typically cold winter air is also coming into the container as combustion air so on average I don't think the ambient temperature would go much above say 30C, so I don't think this is a big factor in this particular case.
> 
> ...


Please send pictures in any case. I forgot to mention that thermal stress (rapid hot cold cycling) is also a failure mechanism.
Cheers


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## joe-nwt (Mar 28, 2019)

So I used the oscillating tool to slice of the heat sink.










At first I thought well I'll be damned, maybe it didn't start here. Then I popped the plastic cover off.










I don't know what that gel is, even after 15 years it still has the consistency of fresh snot. Moving some of the snot out of the way showed this:










I'm fairly confident that's where it started, some little bit either let go or the snot failed. Anybody know what the snot actually is? I assume some kind of insulator.....


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## EJPHI (May 7, 2008)

joe-nwt said:


> So I used the oscillating tool to slice of the heat sink.
> 
> View attachment 152984
> 
> ...


The snot is silicon gel which is thermally very conductive but yet a goos electrical insulator. It is used all the time in high powered circuit modules like this. I see some oxidation on the board which may also have contributed.


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## Forge Boyz (Nov 7, 2014)

It looks like there is a JJN fuse soldered fast to the board. At least I assume it is a fuse.

Sent from my SM-G970U using Tapatalk


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## gpop (May 14, 2018)

Forge Boyz said:


> It looks like there is a JJN fuse soldered fast to the board. At least I assume it is a fuse.
> 
> Sent from my SM-G970U using Tapatalk


Dc buss fuss


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## gpop (May 14, 2018)

Pic of a drive that has moisture damage. (rusty and corroded to the point that some of the fans have seized)









This is one of 3 drive we are planning to changing out due to moisture damage (equipment in the room that caused the moisture problem was removed before i started at this company so 3-4 years ago). These are still running as we had to wait on the new drives and they have run like this for at least 3 years.
We are going to have to bench test / pre-program the new drives as we are changing to Ethernet controls and have a max window of 3hrs to replace the drives, breakers, fuses and to remove the old controls. Programmer has a additional hour to set and test the drives so its going to be a fun day.


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## joe-nwt (Mar 28, 2019)

Forge Boyz said:


> It looks like there is a JJN fuse soldered fast to the board. At least I assume it is a fuse.
> 
> Sent from my SM-G970U using Tapatalk


It's actually bolted on on the other side. Mounts are soldered.


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## JRaef (Mar 23, 2009)

That's an IGBT failure. Could be a voltage spike on the output wires (i.e. someone connected line voltage to the motor while the drive was still connected), but more likely it was secondary to a DC bus capacitor failure, because they have a typical 7-10 year lifespan. When the DC bus caps fail, you get high ripple on the DC bus and that over heats the transistors, causing them to fail shortly thereafter.


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## Flyingsod (Jul 11, 2013)

joe-nwt said:


> That same customer has at least 7 more of the same drives all the same vintage. One other drive was replaced by me in 2011 but the rest are still running.


If the system won’t run with one or two drives down have him get a standby replacement. Drives that old can’t really be considered reliable. My opinion on that sort of thing is that the rest of the lifespan is a total crap shoot. I used to tell customers “it’s unknowable, might last three more hours, three more days or three more years. I wouldn’t stand next to it while it’s running....”

In any case let the customer know you aren’t standing behind it. 


Sent from my iPhone using Tapatalk


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## SWDweller (Dec 9, 2020)

joe-nwt said:


> Omron 3G3MV driving a 10HP motor at 208V. Customer asked if there was any way to tell why the drive failed and if it could have been prevented. Wondered if dirt or moisture might have had anything to do with it failing. I suggested he got 15-16 years out of it, maybe that's to be expected but I'd take it apart and look.
> 
> View attachment 152954
> 
> ...


We had a bunch of Parametrics Drives, (Pre ABB) in a concrete vault 50' underground next to 6 1.5 million gallon concrete tanks used for thermal storage. Could not keep caps in them. We determined that the constant heating and cooling with lots of humidity was the culprit. We drove the warranty people bug eyed. Finally our boss told the partner and me to see if we could stop the problem. What we settled on was removing the caps putting them in a Hoffman 4x enclouser with a heater. Problem solved.
ABB came along and purchased Parametrics and solved all of our enviroment problems with coated boards. Costs a bit more but the enviroment does not effect the boards at all. 
The very first drive we got from CH 400hp 480v freestanding was rated at 40C. Stupid me since it was number one I sat down and read the manual. Found the 40 C and called the support number. Surely this is a mistake. No it is not. I explained it got a LOT hotter than that where we were going to install it. The guy laughed, told me not to put it outside. That is inside the building with the swamp coolers running. Well maybe a slight exaggeration but not much. We ducted air conditioning into the bottom and let the fans exhaust the heat and air out the top.
We discovered that in Phoenix Arizona ducting air conditioning into a drive was a good way to solve a lot of problems. That and never buy a drive without coated circuit boards.


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