RPC randomly keeps shutting off

Very new to machining in general but bought a bunch of machines recently and trying to get things sorted out. I have a mill/surfacer for milling automotive heads that I finally got going.

I purchased a WNY 20hp RPC (I know they are frowned upon, but all I can afford for right now), and I picked up 20hp 3phase motor (Electrum, spelling is off I think). It was brand new but older model, around 2014 I think. Sat in storage for years at a commercial laundry mat a guy was closing. I got it all wired up and seems to be working great. The first night I had it running 2-3 hours without issues. I had decent size loads on the machine and all worked well.

The next night and every day since it will randomly just shut off. If I go back to the RPC panel and turn it back on again, it will come right back on and work. It is not load dependent; today I had it running for 5 min and was essentially just adjusting the Z travel on my mill (power fed) and then it shut off. Sometimes it runs 5 min sometimes 30 sometimes an 10min. It does seem like its getting worse though.

I called the RPC maker, and he said theres nothing that should be shutting off the RPC. There's no safety switch or thermal protection or anything like that. Said to double check theres not a loose connection as one it loses power it WILL not keep trying to restart. I of course looked, but didn't see anything.

Nothing is getting hot at all. I have everything ran with 6 gauge wire and the big 30, maybe 50amp plugs I forget. 100amp breaker for now. Nothing is tripping etc.

Any idea what to look for? I've only used that one machine for right now as I haven't had time to access/setup the other machines yet.

One other note, I've noticed at times when I go to start the RPC, the idle motor acts like it wants to spin backwards sometimes. It will sort of get "locked up" and not move but clearly wants to go one way, but then another, then another...like its fighting itself; but never moves. I generally stop trying to start it...kick it over with my foot then start it and it starts immediately. I have a feeling that is somehow related to my problem as well.

Sounds like either the starting capacitors are failing, or have a loose connection.

It sounds as much like there is a loose connection in the control circuit for the RPC. I assume there is a main contactor to turn it on, and clearly if that drops out, it is going to stop.

If the power to the capacitor contactor drops, it will not start.

Common thread here is potentially a control power supply issue. Likely a bad connection, might be something else similar.

sounds like a failing contactor coil.

I have never seen a over-load relay in one of those pre-built RPC's. Reason is expense. An over-load relay out of adjustment would shut down the unit.
A little tweak on a thumb wheel would fix that. You don't have that type of relay but you can easily add one.

Your unit:
Voltage sensing relay, some capacitors, start capacitor contactor and main contactor.
20Hp Rotary phase converter kit 230vac
I like the way they display such a small image of components and use the term heavy duty.

Torque all connections first. My connections here had to be re-torqued a few times because of soft copper stranded wire. You think it's tight then it becomes loose.
Happened to me about 5-6 times.

Not a fan of voltage sensing relays. A simple start/stop button arrangement is more reliable. You can do that yourself.

Another option: look at possible brief - very brief - interruptions in your electrical service. This converter panel probably has a hold-in
contactor, and you have a power dip as short as 1/10 of a second (hardly visible in, say incandescent lighting) the contactor will drop out,
but re-start when you hit the start button.

If you've noticed short power dips recently, this is probably cause for your converter shutting off.

Thanks for the responses. Been so buys with life I haven't had time to further investigate.

I checked all the wires on my idle motor when it was shutting off. One leg of the wires was just barely warm. It was so close to barely being warm I wasn't sure I was feeling it in my calloused hands and had to use softer tissue of my forearm to really see if it was warm...and it just barely was.

I rewired the connections to the idle motor and a better fashion, and its not even warm at all now.

It continues to shut off. I rewired ALL of the skimpy connections from the start button to the main contactor (that apparently energizes a coil behind it to make the contact; much like a relay I see). That main contactor has 3 "terminals" The very left one is empty except for connections going to the start/stop. The next to are the L1 and L2 from my home panel with single phase.

With the plastic cover off I can see the contactors being pulled in and release. Peculiarly I noticed that when the RPC is running, the very left contact/terminal has very small blue "sparks" coming from within it while it is running. They are very small in length, but a very solid, bright blue light being emitted.

I'm going to assume that "sparks" in any type of electrical work is never a good thing, nor intended. I could understand if it was right when the contactors were engaged, but shouldn't be while its running I would assume.

Safe to say that's what my problem is? Just replace the start/stop and the contactor and move on?

One usually wants a low power contact for a low power circuit, like the typical "auxiliary" switch on a contactor. But I have gotten away with what you are apparently doing for years, so....

Sparks indicate a poor or intermittent connection, possibly affected by vibration. That could account for it shutting off. I'd check the contact for proper function, clean it, and see if that fixes the issue.

If not, then replacing the contactor with one having an "aux", or possibly adding a small relay just for the control system should deal with it. Wire it across the main contactor coil. (I don't really like that second idea, but it would "usually work". It is not positively indicating whether the main is pulled-in or not, it only shows whether it "should have" pulled in)

Sparks indicate making and breaking if contact.

Take several photos of unit then remove contactor.

It may be not pulling fully closed or a contact is bad.

If chicom unit replace with good one since it is out, they are common items and it expensive.

There are motor starter types that are better with protection, that would be better option

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