Help!! Rotary Phase Converter

My rotary phase converter stop working. When the swich is turned on the contact relay clicks rappidly. I can hear the motor spinning, but sparks come from the relay (A) and (what I believe is) the low voltage supply (B). http://i259.photobucket.com/albums/hh317/balancetheherb/tim/Panel.jpg
I took the relay apart, because of coarse it breaks on a friday night when I needed it the most,to see if it was repairable. The origanal damage made a contact weld together. So I repaired it (C) http://i259.photobucket.com/albums/hh317/balancetheherb/tim/Contact.jpg
With no luck, it did the same thing as when i t first went bad, same sparks and rappid clicking. I did mange to get the motor to start and work by forcing a clamp on the contact point of the relay (D) http://i259.photobucket.com/albums/hh317/balancetheherb/tim/Hack.jpg

I tried replacing the contact relay with 2 new ones. Both with same results as the old one, same sparks and rappid clicking. Which leads me to believe that it's not the relay. http://i259.photobucket.com/albums/hh317/balancetheherb/tim/Contact2.jpg
This is where I get lost. I have no idea where to go from here. Any help or suggestion would be appreciated

To really get to the heart of this a wiring diagram is going to be needed...the diagram from which you built the RPC. How are you switching the start capacitor in and out of the arrangement? (I am guessing "B" is a potential relay)

I suspect you have a short circuit somewhere (possibly in the potential relay), leading to the sparking and the melted contacts on the ice-cube relay. Or...the relay is doing a lot more switching in terms of amperage than it is actually rated for.

The other problem that might be happening is that the potential relay is actually welded internally causing the start cap to constantly be "engaged". Better practice is to use a separate amp-rated contactor to switch the starting capacitor in and out of the circuit rather than relying on the potential relay to do the "heavy lifting".

Also, I would not trust an ice-cube relay for switching motor loads for very long. I posted another recently about it being a quick-fix solution in desperation, but an IEC or NEMA motor starter are always better choices IMHO.

Thanks for the quick reply. I didn't make this one , I bought it complete minus the 3 Phase motor. I have other motor contact starters that I could use. Is it as simple as once the 3 phase motor is spinning it will produce the 3rd leg of power needed. Or is there more to it that I'm not aware of.

There sure seems to be alot of componets in this convertor , relays, low-voltage coil and capistator.

Well here's my advice... don't take my advice.

Sounds like a problem with your capacitors. It could also be a shorted winding in your RPC motor.

Are you trying to start the phase converter with any sort of three phase load turned on? Anything, even a transformer, should not be connected to your phase converter when you turn it on. You should start the RPC and then throw the switch to energize whatever is behind it.

Grab yourself a reliable little multimeter and set it to measure ohms.

Try to check your motor windings for an open or short.

If that's not the issue, you might try checking each capacitor for short or leakiness. Disconnect each capacitor one by one and check resistance across the connections. It should be O/L.

Thanks I'm going to check it right now. I may have had the pump running on the lathe which may be causeing the problem your referring to.

Unplugged lathe ,same clicking/ sparks. Checked caps with meter and these are the readings.
http://i259.photobucket.com/albums/hh317/balancetheherb/tim/Ohms.jpg

Both readings where getting higher didnt wait to see if they stop.

NewbieMachinist said:

Is it as simple as once the 3 phase motor is spinning it will produce the 3rd leg of power needed. Or is there more to it that I'm not aware of.

There sure seems to be alot of componets in this convertor , relays, low-voltage coil and capistator.

Click to expand...

Yeah it's pretty much that simple. Here's an example. In my dad's shop we used to have a big three phase pedestal grinder for chamfering bars. If you had the RPC's going it would fire right up. If not, and you turned it on, it would sit there and single phase the motor.

However, you could take and spin the thing up by hand to about 300 rpms and then turn the switch. It sits there and grinds and hums and burns and churns itself up to full speed after about a minute.

Now once that thing is started on single phase, it's generating power on the third phase. You could check three phase voltage and you'd have the signal. The voltages would be totally out of balance, of course, but the signal is definitely there. That running pedestal grinder was enough of a phase converter to start up some other three phase load, provided it was really small. Of course they churn and grind and hum and rattle and slowly come up to speed.

What your modern phase converter has is two banks of capacitors. One bank acts as a motor starter by delaying the timing of a portion of the power input and applying it to that third winding. The second bank balances the voltage of the three legs once the phase converter is running.

It's been a few years since I joked around with RPC's. I think the other guys have good suggestions. Maybe cruise eBay for some higher quality motor starters.

You said you managed to get the motor to start when you hacked it with the clamp, right? How did it run then?

every thing ran and sounded fine.

So where do you think the problem is?

I told you not to take my advice! It's probably the contactor circuit like everyone else said.

apestate said:

So where do you think the problem is?

Click to expand...

I put a new one in and it didn't work. So its not the relay. I'm thinking it may be the low-voltage supply. It's not keeping the reley closed(or open). But when I clamp it I'm doing the same thing the coil is suppose to be doing.

The coil needs power to work and I believe it gets it power though the relay. Kinda a catch 22 for me. If I can dig up another low voltage coil I'll try one of the new relays.

thanks for making me think about it.

Gota go get a hair cut wil try it as soon as I get back

By low voltage supply I'm guessing you mean there's a little "control transformer" or whatever to supply single phase power at 120 volts or whatever to the control circuitry. Is that right?

You said the relay clicks rapidly, too. I wonder if there's a screwy connection in the "holding" circuit that keeps the relay closed once you have pushed the button in. It might be something that's just vibrating on/off.

Take your time. It sounds like you can run your machine if you have to. Just be careful and study the circuitry carefully, take notes, and figure out what the problem is.

Industrial control circuitry was really difficult to work on, for me. Once I learned it I enjoyed it so much that I would purposely seek out motor starters on ebay to have an excuse to work on Brown & Sharpe industrial control cabinets. I loved it. You don't know the feeling of power when you open up one of those boxes and understand what's going on.

Get you a nice multimeter, maybe a light bulb with test leads, and a notepad. And be meticulously careful.

All the more reason to use a simple system to start the RPC. I turn on a motor to spin the RPC, then turn the voltage on to the RPC, then turn the motor off. All the fancy stuff you have will fail sooner than mine will.

It's nice to be fancy but it's better to be simple. KISS

Yeah but you'd still want a capacitor circuit to balance the three phase power under load. At least, that would be better.

Rotary phase converter setups are pretty simple. Plus, if you're bound to use one, the more you know about it the better off you are.

You can do some pretty neat things like putting the run capacitors on each load you start up to help balance the system neatly. Of course, you have to set that up with a control circuit and use a contactor to avoid certain problems.

May, or may not...

Hi All!

Carl- if it's done RIGHT, an automatic-starting, properly-protective RPC will last longer than relying on the operator to properly sequence and start. Prime example would be if you (or someone using your converter) were to use an improper sequence, or attempt to start with a load engaged., or having a power failure amidst operation, or a few other fault conditions.

This problem sounds more like the starting-cap relay circuit isn't strong enough for start cap current... but without having a good schematic of how it's really hooked-up, it's just a matter of guessing.

Starting caps carry an incredible amount of current. In the case of 10hp+ idlers, running a pony-start really does make sense, as the starting current is much lower. In ANY case, it is best (and proper) to have two BIG contactors on the RPC- one that controls power coming IN to the RPC (controlled by start and stop buttons and a latching-relay type circuit), and one going OUT to the tools.... with a timer... to assure that the machine is not started with a load engaged, and also so that it shuts down in the event that gnerated phase is lost.