Help! My rotary phase converter made smoke!

[poppinjohnnies]

My lathe & mill came with a home built phase converter that worked great in the prior owner’s shop. I just wired it in my shop and it appeared to work fine, but the output voltages were 120, 121 and 173. Then I fired it up again yesterday and it apparently blew up a capacitor. Does anyone have knowledge on these things?

 

[sberry]

Hmmm,, I think it's broke.

 

[wyliesdiesels]

that looks to be more than a capacitor.

were you measuring line to line or line to ground?

Do you have a schematic and pics of all the wiring and connections?

how and where did you connect the incoming power?

unfortunately, since this is home built, its gonna be hard to diagnose over the internet

 

[Bert_]

I take it that's the control panel?

Generally you measure voltage line to line. Most equipment that would need a phase converter doesn't use neutral, so no reason to measure to it.

 

[Dagny]

Iv'e seen capacitors make that kinda smoke. How many are there?

 

[nadogail]

When the factory installed smoke leaks out of electrical equipment they seldom if ever recover.

 

[poppinjohnnies]

that looks to be more than a capacitor.

were you measuring line to line or line to ground?

Do you have a schematic and pics of all the wiring and connections?

how and where did you connect the incoming power?

unfortunately, since this is home built, its gonna be hard to diagnose over the internet

Ok, incoming power is from my sub panel via 50A breaker. No schematic. I was measuring from line to ground. One of these capacitors has oil on the top and it looks like some got onto the inside of the cabinet. Here are some pics. There are 2 banks of capacitors - left & right side. The start caps on the left are pictured removed. The right side are run caps I suppose.


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[7635tools]

If you see oil on the capacitors, I would check each one to see if they are still good. You’ll need a meter that can read capacitance.


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[poppinjohnnies]

If you see oil on the capacitors, I would check each one to see if they are still good. You’ll need a meter that can read capacitance.


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Ok. I have a friend who has a meter that can check caps.


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[The Cobbler]

if the caps smoked I would expect visual evidence

 

[Bert_]

One of those contactors is probably for the start caps. Make sure it's not staying on. 10 seconds is about the max for a start capacitor. In a phase converter I wouldn't expect it to stay in circuit for more than a second.

 

[larry_g]

http://metalwebnews.com/howto/ph-conv/ph-conv.html

read the above link to understand a bit of basic information on rpc's.

Another thread, https://www.garagejournal.com/forum/showthread.php?t=367420&highlight=hanrahan

lg
no neat sig line

 

[poppinjohnnies]

Ok. Will do. I'll test & replace the caps that are bad and then check time on the contactor.

 

[TuxThePenguin]

If you see oil on the capacitors, I would check each one to see if they are still good. You’ll need a meter that can read capacitance.

Capacitance meters cannot tell you if an electrolytic is good. It's impossible to be sure.

It can sometimes tell you if they are bad, but if the capacitance reads in the right range, it doesn't mean that it's good.

You need an ESR or leakage tester to be reasonably sure. They will find bad capacitors that still happen to measure correctly with a simple capacitance tester.

In electronics repair, this actually happens so often that I think it is misleading at best to suggest measuring the caps this way. These caps are still electrolytics like the stuff I often replace in electronics... just larger.

What I would go by if I were personally there is the smell. Capacitors smell a lot different than cooked wiring or ICs.

 

[rlitman]

Ok. Will do. I'll test & replace the caps that are bad and then check time on the contactor.

I'd replace ALL the caps. For AC caps, get something with a metal case that you can ground. Those caps are ANCIENT, and have long since outlived their expected lifetimes.

 

[matt_i]

One of those contactors is probably for the start caps. Make sure it's not staying on. 10 seconds is about the max for a start capacitor. In a phase converter I wouldn't expect it to stay in circuit for more than a second.

This is my thought here. If a time-off delay or "potential relay" was used to "sense" the 3rd leg's voltage and wasn't connected or could not "sense" then the start caps are in a bad position. When I ran an RPC I used a 1 second delay on the timer-off relay.

This is my original RPC circa 2003.

https://metalwebnews.com/howto/phase-converter/phase-converter.html

 

[Bert_]

I'd replace ALL the caps. For AC caps, get something with a metal case that you can ground. Those caps are ANCIENT, and have long since outlived their expected lifetimes.

Only run capacitors come with a metal case. The op's problem seems to be start capacitors. The ones in his picture look pretty modern. The label looks like BMI which are good capacitors.

 

[poppinjohnnies]

Well, I replaced that capacitor and I already blew up the new one. Obviously, something is amiss. Here’s some pictures of the guts. The start caps on the left are disconnected in this picture.



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[Norcal]

At the practical machinist website there are a number of plans for RPC’s posted, it might be a good time to sit back and start over, some of the posts in the past at PM, had builders who were a little to clever IMHO in fabbing parts, one used ground bar kits and PVC pipe to make their own terminal blocks which is not code compliant. There are plan sources at the OWWM forum too.

 

[nadogail]

IMHO, it may be time to make your own RPC using new capacitors and many of the components of the original.

When you finish you will know what you have and how it went together.

 

[wyliesdiesels]

I agree with the others

Time to do a tear down and rebuild

This is something thats much to hard to diagnose over the internet without a lot more info, labels, pics, etc etc

 

[Bert_]

Well, I replaced that capacitor and I already blew up the new one. Obviously, something is amiss. Here’s some pictures of the guts. The start caps on the left are disconnected in this picture.



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Did it blow up immediately or did the converter start and run for several seconds before the capacitor failed.

 

[ez-duzit]

For information on this why would you not contact the person who designed and built it, and then sold it to you?

 

[alfredeneuman]

Just an aside:

The panel (3rd photo, post 7), doesn't appear to have enough working space (30" wide. 36" deep). If you move the machine slightly to the right (of the photo) it would take care of it.

 

[poppinjohnnies]

Did it blow up immediately or did the converter start and run for several seconds before the capacitor failed.

It fired up once and it powered up the lathe just fine. I shut it down and fired it up again about 20 minutes later and it blew the cap. The same thing happened the first time it blew a cap.


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[poppinjohnnies]

I agree with the others

Time to do a tear down and rebuild

This is something thats much to hard to diagnose over the internet without a lot more info, labels, pics, etc etc

I’ve thought about that. I have another RPC that I built myself, but the slave motor is too small to run the lathe, let alone the lathe & mill at the same time. I suppose I could take the motor off this faulty RPC and see if my homebuilt unit will run with it. The current motor on it is a 3 hp. It runs my big Gorton mill just fine. The lathe has a 5 hp motor. The slave motor on the faulty RPC is 7.5 hp


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[poppinjohnnies]

Update: I ended up using the 7.5hp slave motor that was on the smoky converter with my home built box. Works great!


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[American Locomotive]

I suspect the time delay relay for the start caps or the contactor for the start caps was stuck on, keeping them in circuit.

 

[Renegade1LI]

Time to switch to a vfd.

 

[misterfixit]

Time to switch to a vfd.

I think the OP has more than one 3ph machine to run. I would stick with the RPC to run multiples rather than buy a VFD for each.

 

[Norcal]

I think the OP has more than one 3ph machine to run. I would stick with the RPC to run multiples rather than buy a VFD for each.

There are some who use a VFD for more than one piece of equipment but in my opinion that is asking for trouble.