# Pm 932 Capacitor Explosion



## Jay-z (Apr 22, 2016)

And I thought it was going to be a dull evening. Had a capacitor go bang on my PM 932 in the middle of a small project I was working on. Definitely got my attention, as if the smoke didn't. One second the motor sounded different and then it happened.


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## Iceman (Apr 22, 2016)

breakdown of the dielectric / overheating induced gas buildup?


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## Jay-z (Apr 22, 2016)

Iceman said:


> breakdown of the dielectric?


No idea, I'm not an electrician. I did check all of the connections and they were tight. Motor ended up screaming hot. Sounds like a phone call to Matt.

Jay


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## Iceman (Apr 22, 2016)

Time for a 3phase VFD upgrade?


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## rwm (Apr 22, 2016)

I had no idea those caps could explode! Crazy.
R


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## Iceman (Apr 22, 2016)

had a polarized dc cap blow after installing with the wrong polarity - like a shutgun going off.


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## Jay-z (Apr 22, 2016)

I'm letting everything cool off for a while before I get under the hood. 

Jay


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## Iceman (Apr 22, 2016)

Jay-z said:


> No idea, I'm not an electrician. I did check all of the connections and they were tight. Motor ended up screaming hot. Sounds like a phone call to Matt.
> 
> Jay



Does sound like an overheating induced failure - it is my understanding that in these installations the capacitor is used for motor starting, the overheating may have led to the failure of the capacitor but it may only be a symptom of a larger problem that led to the overheating to begin with (bearing failure?).


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## wrmiller (Apr 22, 2016)

I'm also no motor expert, but start capacitors are supposed to be 'disengaged' (for lack of a better term) after the motor reaches some rpm threshold. I have been told that if the capacitor is not disengaged, things like this can happen.


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## Iceman (Apr 22, 2016)

The more I think about it, the more likely this capacitor is being utilized as a "Run" capacitor versus a "Start" capacitor. Start capacitors typically have a relay that disconnects the capacitor from the motor after start - a Run capacitor remains connected. If the capacitor wasn't up to spec or was failing this could have led to the motor not running properly (leading to overheating).
I'm standard AC, but mostly a DC guy when it comes to electrical projects. That said, my degree was based around electronics (Microprocessor/uController design and implementation - Industrial automation, etc).  Which means I mostly know enough to get myself into trouble.


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## mksj (Apr 23, 2016)

I believe it is the start capacitor, there is normally a centrifugal motor switch which disengages the start wingdings when the RPM reaches a specific  speed ~90% of rated speed. As Bill mentioned, if the switch doesn't disengage the capacitor will overheat and the motor will get vey hot. Usually there is a safety plug that will vent electrolytic capacitors, but if they fail shorted, they can explode. Too frequent start/stop cycles can also overheat the capacitors and they can go south pretty quickly. I would also check the wiring, some of it looks darkened.


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## silence dogood (Apr 23, 2016)

Electrolytic capacitors have gel or liquid filled paper that is called an electrolyte. When something goes wrong, the gel or liquid gets hot and turns into vapor.  Therefore boom.  A voltage surge could have caused this.  A defective motor could draw more current than the capacitor could handle.  When you buy a new capacitor, make sure the voltage is the same or higher.  The capacitance should be within 10 to 15% .  This is for an AC circuit, make sure it is for AC.  Electrolytic  capacitors are usually polarlized and show + on it.  AC electrolytics  are made a certain way, its like two capacitors back to back.  Also electolytics  have a shelf life, so if you can, get the newest one.  I've worked in electronics for over 40years, so I hope this little knowledge will help.


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## Iceman (Apr 23, 2016)

Goes to show tequila and troubleshooting don't mix.

Interesting info/video.

http://www.capacitorguide.com/motor-starting-capacitor/


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## TOOLMASTER (Apr 23, 2016)

They do that sometimes...looks pretty dry


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## uncle harry (Apr 23, 2016)

Iceman said:


> had a polarized dc cap blow after installing with the wrong polarity - like a shutgun going off.




That was probably a tantalum cap. They make great gag car bombs but are pricy.


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## Jay-z (Apr 23, 2016)

I am more interested in finding out why it happened.  If I go and just replace the capacitor then there is a good possibility that it will happen again. I need to find the root cause of it.   I am sure that it is not from too many on off cycles.  I am in no hurry  with these projects .  You know the old saying measure twice ,cut once.There's a lot of time in between cuts.  And I hope that I wasn't overloading the machine milling a piece of aluminum with a 3/8 carbide endmill. Maybe it is time for that 3 phase VFD.

Jay


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## Jay-z (Apr 23, 2016)

mksj said:


> I believe it is the start capacitor, there is normally a centrifugal motor switch which disengages the start wingdings when the RPM reaches a specific  speed ~90% of rated speed. As Bill mentioned, if the switch doesn't disengage the capacitor will overheat and the motor will get vey hot. Usually there is a safety plug that will vent electrolytic capacitors, but if they fail shorted, they can explode. Too frequent start/stop cycles can also overheat the capacitors and they can go south pretty quickly. I would also check the wiring, some of it looks darkened.


 You are correct with some of the wire being darkened .  Seems that things got quite hot .

Jay


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## John Hasler (Apr 23, 2016)

These failures are almost always the result of a stuck centrifugal switch.


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## rherrell (Apr 23, 2016)

I agree with checking the centrifugal switch, I have that same machine and FYI the switch is on the bottom so you will have to remove the motor to get to it. Here's a link to a video about repairing it...


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## rwm (Apr 23, 2016)

That video is really outstanding. I have bookmarked it for future reference.
R


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## Jay-z (Apr 23, 2016)

Going to remove it from the mill today for further inspection. That burnt electrical smell is terrible.  To Be continued...................


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## wrmiller (Apr 23, 2016)

Hey Jay-z,

I too am more of a low-voltage/microcontroller guy and didn't really want to deal with 3-phase A/C and a VFD, but after having done two, I'm sold. Better than sliced bread...


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## Jay-z (Apr 23, 2016)

Well, from what I see it looks like the centrifugal switch decided to stick overloading the capacitors and overheating the start  windings .  They both look a little overheated and have a burnt smell . 

Jay


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## wrmiller (Apr 23, 2016)

Ouch... Pretty much what I figured, but it still sucks.


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## John Hasler (Apr 23, 2016)

Your run cap is ok.  The windings are probably ok as well but there's probably a fusible link buried in there somewhere that will have to be replaced before you can put the motor back in service (with a repaired centrifugal switch, of course.)    DONT bypass the link.


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## mksj (Apr 23, 2016)

Would consider getting a new motor at this point. If under warranty should be able to call QMT, otherwise I believe Leeson makes a 3 phase metric flange style in a 1.5 and 2Hp that should match your current motor dimensions (check yours against the ones listed below) . You may find that a 3 phase motor with an inexpensive VFD may be close to the same price if you need to purchase a new single phase replacement motor. Having variable speed, soft start/braking and slightly higher top speed would be like having a new machine. Although the Leeson metric motors are of Chinese origin, many people have upgraded their machines with their metric motors, I have heard of no quality or reliability issues.
http://www.electricmotorwholesale.com/LEESON-192065/
http://www.electricmotorwholesale.com/LEESON-192206/


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## coolidge (Apr 24, 2016)

Jay-z said:


> I am more interested in finding out why it happened.  If I go and just replace the capacitor then there is a good possibility that it will happen again. I need to find the root cause of it.   I am sure that it is not from too many on off cycles.  I am in no hurry  with these projects .  You know the old saying measure twice ,cut once.There's a lot of time in between cuts.  And I hope that I wasn't overloading the machine milling a piece of aluminum with a 3/8 carbide endmill. Maybe it is time for that 3 phase VFD.
> 
> Jay



Recommend you check into a made in USA Baldor motor for a replacement. Pricing is all over the map on Baldor motors and internet sellers are frequently way over priced. I purchased a 2hp Baldor replacement motor for my lathe, not your average motor this is Farm Duty rated sealed and gasketed for nasty farm environments. My local 2 man motor repair shop sold me this for like $324, there's a Baldor warehouse in my area (Portland, OR) and they had these in stock. I drove over and picked it up the same day. Some of the crack smoking on-line sellers wanted over $1,000 for this motor plus shipping. Sometimes it pays to buy local. I bought a cast iron Baldor stand for my grinder from them also, again way cheaper than anyone online and it was in stock.


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## Jay-z (Apr 24, 2016)

Coolidge, 

Finding anything reasonably priced in the Washington DC area is always an adventure. I'm not saying it can't happen, but it is unlikely.

Jay


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## Ulma Doctor (Apr 24, 2016)

motor caps are frail creatures. 
i'd consider popping a 220 or 250 uf capacitor in it and run it
check belt adjustment or any source of bind, the centrifugal switch will stay open until the motor comes almost up to full speed- any binding may prevent that.


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## TOOLMASTER (Apr 24, 2016)

WONDERING if the motor voltage was changed but not the cap to correspond with it


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## mksj (Apr 24, 2016)

Motor is a metric D flange mount direct drive 90S size, per the manual the capacitors are rated for an input voltage 240VAC, this issue as mentioned was the stuck centrifugal switch. Short of hunting on eBay and finding a metric single phase motor, which is very unlikely, it is doubtful you will find a  replacement on someones shelf. Another individual who had a single phase RF-45 was looking to switch to a 3 phase motor, the Leeson metric flange mounts listed matched the mounting dimensions, but would need to verify the shaft size/configuration. Since the motor is still under warranty, first step would be to contact QMT and see where to go with it. Doesn't matter how good the start capacitor is, it is going to fail if centrifugal start switch does not disengage. This one went out with a bang.  Electrolytic caps all have a finite lifetime, heat and age kill accelerate their demise, there are also different ratings and specs if used for DC or AC.


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## Jay-z (Apr 25, 2016)

After a quick and easy phone call to QMT  there is a three-phase motor and VFD on its way to my house . Now the fun begins.

Jay


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## wrmiller (Apr 25, 2016)

Oh Mark...Jay may need a bit of help with a schematic.


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## Rich V (Apr 25, 2016)

We should all chip in and buy Mark a case of beer or wine, the man deserves it!




wrmiller said:


> Oh Mark...Jay may need a bit of help with a schematic.


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## wrmiller (Apr 25, 2016)

When I finally get back down there (AZ) I will show up at his door with an Adult Beverage of his choice (maybe a 15 year old single-malt?).


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## Jay-z (Apr 25, 2016)

wrmiller said:


> Oh Mark...Jay may need a bit of help with a schematic.


 Have a little faith, buddy .  I just went and picked up a wiring for dummies book. That should cover most everything.  And if it doesn't, there's always YouTube.  No worries here .

Jay


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## wrmiller (Apr 25, 2016)

No prob Jay. 

When I did my first machine, the lathe, I had absolutely no experience with VFDs or lathe logic circuits. So Mark was a big help there. My mill was a much simpler beastie that I managed to do myself.


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## mksj (Apr 25, 2016)

wrmiller said:


> Oh Mark...Jay may need a bit of help with a schematic


Already on it. He needs to give some thought to control options. The most typical would be 3 wire control, momentary On and Momentary Off buttons, use the current spindle power switch to set the direction, or  just using the current For-Stop-Rev switch wired directly wired to the VFD  input terminals for sustained ON controls. If the latter, would need to program the VFD to prevent an auto restart on power failure. Could also do a 3 button momentary  that I have used on lathes FOR-STOP-REV buttons, but would need two relays. Not getting fancy, but it is possible use a small hall sensor to reverse direction for power tapping, my mill came with this.


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## wrmiller (Apr 25, 2016)

Which parameter do you set for no auto restart on power failure?


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## wrmiller (Apr 25, 2016)

Jay-z said:


> After a quick and easy phone call to QMT  there is a three-phase motor and VFD on its way to my house . Now the fun begins.
> 
> Jay



Ya just gotta love Matt and QMT (well I do anyway...)


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## Jay-z (Apr 25, 2016)

Leaning towards to three wire control with the momentary on and momentary off buttons  with the current power switch to be used for forward and reverse. Just Trying to keep it simple .  No need to reinvent the wheel here .


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## wrmiller (Apr 25, 2016)

I did a very simple circuit on my mill, using a fwd/off/rev switch, 10k pot, and a e-stop. No relays. Similar to my lathe. So I was just asking Mark (sorry for the slight O.T.) which param to set to prevent a restart in the event of power failure as this could be useful.

Are you using the momentary on/off buttons as a jog or tapping feature?


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## mksj (Apr 25, 2016)

Hi Bill,
So there are two different parameters that I use to address what happens in a power loss and prevent machine restart. The first is to configure an unused terminal  input for the Option Code 13 which is the Unattended Start Protection (USP on page 4-25 of the manual). In my lathe builds, I have this tied into the power/control relays so the input is always on on restart/power-up. If a relay is not used, I would have it on all the time (see if this works), or it could be activated when the Forward/Reverse was ON if using a sustained direction switch and two logic diodes as shown below. 

The other command parameter to change would be B050 should be set to "02", this tells the VFD that on a power loss to brake the motor to a stop using the regenerative power generated from the motor. Page 3-64 of the manual.

My mill has a separate tapping function on the spindle switch, it turns the motor speed down and uses two hall sensor to set the reverse point and also shuts the motor off after the tap. It is a BLDC, but works very similar to a VFD. It uses a monetary guarded button for on and a separate unguarded one for off. I like this arrangement. If you think you are going to do power tapping, then there are other possibilities on how to do this.


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## wrmiller (Apr 26, 2016)

Hmmm...I think I have a couple of diodes left from the lathe re-wiring. Thanks!


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## Jay-z (Apr 28, 2016)

The VFD and three-phase motor have been delivered.   Still waiting on a handful of other supplies for this project.  Have already begun the process of figuring out where things need to go and what controls will be used . Should be an interesting project. 

Jay


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## CraigB1960 (Apr 28, 2016)

Jay-z said:


> The VFD and three-phase motor have been delivered.   Still waiting on a handful of other supplies for this project.  Have already begun the process of figuring out where things need to go and what controls will be used . Should be an interesting project.
> 
> Jay


Jay, I certainly look forward to seeing this project as it progresses!  Please keep the updates coming!


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## Jay-z (Apr 29, 2016)

When things finally get moving with this project I will create another thread in the PM forum to show  progress of the upgrade.  With that being said this is my first VFD installation  of any kind  so suggestions and opinions are always welcome .  I have an idea in my head on what I want it to be,  making it reality is something different. Planning on keeping  the installation clean and simple.   With guidance from other forum members that are happy to share their knowledge about VFD's, I believe this  will be a smooth transition . Stay tuned.........................Jay


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## planeflyer21 (Apr 29, 2016)

Jay-z said:


> The VFD and three-phase motor have been delivered.   Still waiting on a handful of other supplies for this project.  Have already begun the process of figuring out where things need to go and what controls will be used . Should be an interesting project.
> 
> Jay
> 
> ...



Those are much smaller than I had imagined.


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## wrmiller (Apr 29, 2016)

That is a great VFD IMO, (I have two) and I too was surprised at how compact it is.


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## ch2co (Nov 22, 2016)

How old is your mill??  Warranty ?


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## Jay-z (Nov 24, 2016)

Received it 7/14
Just replaced the seals in it last week. Seems they were jacked up from the factory. Matt sent out the parts quick and easy. Can't say enough good things about QMT.


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