RPC help....

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Tamper84

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Well boys and girls, I gots a problem with my rpc. It may not be a problem, but who knows. I had an electrician buddy of mine put together my rpc according to a schematic on here. But for some odd reason, it kept blowing capacitors. So, he re did the whole sh-bang, he made me a rpc the "old school" way. It has a 110 starter motor to get the 3 phase idler motor up to speed.

It works, but it came uncoupled today. (it uses a love-joy coupling to join the two motors). Any who, once I seen it came uncoupled, I shut off power to the whole shop. Threw the main breaker!!! No power any where. Reached down to touch the coupling, BAM got lit up :panic:. Dont do that lol:lmao: There are no capacitor's any where in the system. Not balanced, nothing.

So, when using a 3 phase idler motor, generating the third leg, Im guessing it can store some energy. Right? :dunno: How do I discharge this so I can safely couple it back up?

Thanks,
Chris

P.S. Its ok to laugh about the situation, Im fine no harm. But safety first, which I didnt do. I just ASSumed and you just read what happened. NOT good :nono: Always be safe.
 
I think the electrical boys might have a reason for your shocking experience. I have built many RPCs, and allways use a 110 motor to pony start. I have never used a coupler to join the two . The most common is belt driven, with the pony motor on a hinge. Start up the RPC, and lift the pony till the belt flys off. Easyer on the pony not having it spinning wearing out the bearings.

Most I have built were 7.5 - 15 hp, and found that there can be cap issues with start up. With the pony start, I have never had any problems, But, I didn't joint the two motors with a coupler either. With the pony you should be able to spin the RPC up to speed, throw power to it, with out lights dimming, breaker tripping, and no drama.

You say you got shocked by the pony? With out it running, or power?
 
Well as to simply hooking it up, and plus we had a love joy coupling on hand to do the job is the reason why it was used.

7.5 horse power idler motor. And nope, no power at all in the shop. I don't know what motor got me. I pretty much touched both sides of the coupling at the same time. After the shock, I didn't touch it again. :)) At least until I can some how figure out how to make sure its discharged all the way.

Thanks,
Chris
 
Hi there,

Are both of your motors grounded? If not, they need to be, ASAP. This is just as simple as attaching a wire to the frame of the motors, and the other end to the ground in your electrical panel.

This will also ensure that you don't get a shock when you touch them again.

Just out of curiousity, using a voltmeter, are you reading a constant voltage? Or was it just a residual charge?

You should also check your motor leads for continuity between phases, if some exists, then the insulation in the windings has gone bad, and the motor should be replaced.

-Cody
 
Was any motor still spinning when you got zinged? If so, that's the easy answer. A generator is just a motor in reverse.

If all motors were idle, was anything plugged into the system that may have electronics or capacitors in it's circuitry?
 
Yup. Everything is grounded. And nope not spinning or anything plugged in. That's why I'm a little worried lol. I will post a picture of it tomorrow. But I do believe everything is grounded.

How I discovered the uncoupling is that the 3 phase motor wouldn't kick in after I started the pony motor. So I did try to start it. It was before I touched it and before I touch it it was off. Could I have gotten shocked off the start cap in the motor?

Thanks,
Chris
 
Not if everything is wired correctly. Yes, caps can and do store quite a punch, some for a long time. Guys who service AC units and some motor guys I know carry around a large wattage resistor with clips to drain the caps before working on a system, and some others just jam a screwdriver across them. IMO, that's hard on the cap. But, the coupling, the shaft it's on, the bearings it rides in, and the motor housing should NEVER be hot, in any scenario. So, I suggest you do some close examination of the wiring. Possible a ground vs. neutral issue. Remember, there is no neutral on the 3 phase side of things. There is the possibility of some "leakage" of the insulation, even if the wiring is correct, and a hi-pot test should be done to check. If it is severe enough, a DMM can detect continuity between any lead and the housing, and that's a bad thing.

If it was a cap discharge that got you, that's about the only way I can think of for it to happen, so start with the wiring, then go to the DMM, then take it to a motor shop if you can't do the hi-pot test yourself. Some people refer to the instrument for that as a "Megger". Might be able to borrow one.
 
Sounds like the caps on the motor you were attempting to build the RPC for were charged and back fed into the system. Some suitable diodes in line with all three legs will prevent that from happening again. A large start or run cap will definately light you up. When I was a dumb kid we used to charge large TV caps and toss them to people. Could have really hurt someone badly. If you got a jolt and nothing was turning then the driven motor or the driven motor controller has caps somewhere in the system and you should install the diodes to prevent EMF back spikes from damaging your machine and you...

Bob

Put up a schematic and I will show you where to put the diodes to prevent this. The diodes should be only a couple of bucks at the electronics gettin store.
 
the pony motor needs to be turned off when the rpc starts, and make sure the motors are the same rpm or have a disconnect of some kind.
the pony motor becomes a generator of static electricity when in the passive state. add a piece of rebar diven into the ground 18" or better and hook a wire to the motor case anywhere metal and then connect to the rebar or copper rod ,if you want to be correct,for grounding.
 
Yes they are the same rpm. Both of them are 3450. Here's a picture of the setup. I put them behind the shop in the shed. The switches are inside of the shop.

Thanks,
Chris

image.jpg
 
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