3hp RPC putting out very high voltage?

I have a American Converters 3HP model that I need to use with my South Bends.

I hooked it up in my new shop this week (Has been running my lathe in the past, Didn't check voltage before I guess) Anyway, I checked the voltage output of the rpc at the breaker panel and it shows 330 volts AC across the legs.

If I test it from leg to ground, I get 117, 359, 119.

I don't think this can be right. Not for a 220v 3 phase converter. All of my equipment is wired for 220 volt 3 phase.

I'm not finishing the project until I find out what is going on. All that is in the case is a capacitor for the motor. Nothing else is installed in the junction box attached to the motor.

Help!

Normaly a RPC has 220 V Live going from input side to output and the neutral doing the same. this gives you a pair of output wires with 220V on them. The third wire comes from the motor and is the generated phase and is arranged that it is 220V from both the live and neutral.
So my problem is that you don't have the incoming 220V appearing at the output.
Two points does your RPC motor run? and can you measure the ingoing 220V accurately? One other thing, your meter does not take any current to speak of compared to a motor, so the 330V could be some sort of leakage which would drop down to 220V when any amount of current is drawn. ( wire up a pair of light bulbs in SERIES so they operate on 220V and use as a load)
Frank

Still puzzling over your problem. One metering problem is that measuring your voltages to earth will give missleading values.
If you draw a vector diagram using a scale of 1" = 100Volts. draw a vertical line 1.1 ", vertical, at its bottom draw a vertical downwards, 1.19", this represents your incoming 220V, the joint between the two line, being earth or neutral. Thats sorts my input/output 220V!!
Now the generated phase wire can be represented by a point that is 2.2" from both ends of the lines you have just drawn. If you measure the distance between the earth point and this new point it should be about 1.9", i.e. 190V. with your reading of 359 volts, its actually 3.6", i.e. the phase angle is far from 120 degrees. If you extend the line through the earth point and the generated 220V point, and make it 3.59", you will find that the actual distance between these points is enormous, giving a true phase to phase voltage of 236, 500,500 Volts. Does your voltmeter read correctly?
In real life the generated phase point on your sketch can be up or down from the centre of your start point, giving unequal voltages between the various phases.
Frank

You are measuring wrong.

Measure from 3phase line to 3 phase line. Do NOT measure to ground.

A high voltage from ground to the "stinger" lead is PERFECTLY NORMAL, but offers little information about the actual 3 phase line voltage.

Give us the voltages from line to line and you'll probably see you have a far smaller imbalance.

His 117 and 119 measurements would be his incoming 220V. The third voltage is his unloaded generated leg. Measure the voltages between the phases when the load machine (lathe) is under power.

I measured them both ways to get my readings. At this point I do not have any machines moved into the shop as of yet. But when I measure from leg to leg:

I get 220 total from the input line legs. I get 330volts from either one of the inputs to the created leg. These readings were taken at the input side of the 3phase breaker box I have. Confirmed at the junction box of the RPC as well with the Breaker Box disconnected.

I will move the Lathes and my Surface Grinder in the shop this week and try to test with power. My DMM is working fine, I would know very quickly if it weren't with the work I do.

Thanks
Chris

OK, that is high.......

So how is it wired? What size caps are used?

It's a commercial unit, right, not a lashup of a "mystery box" to a motor you supply? What does the manual say about measuring unloaded, and normal readings?

"Stinger" 3 phase is wired similarly to what happens with an RPC.....

One 240V phase is center-tapped, and the tap is grounded to become the neutral. That then produces 120V-0-120V.

The third, or 'stinger" is at a higher voltage to ground, but at a normal voltage vs other phases.

An RPC starts with a 120-0-120 voltage, and makes a third phase which will then be at a similar high voltage to ground. But it should be OK to phases.

if you have a high voltage to ground AND a very similar high voltage (330 vs 339V) to a phase, then something seems amiss.

Either what you think is a phase isn't, or the unit has a compensation capacitor value that resonates it and produces a very high unloaded voltage, or some other phenomenon is happening, such as weird wiring, or some issue with the motor.

My Arco, a one-piece commercial RPC, produces an unloaded voltage a bit higher than, but fairly similar to, it's loaded voltage.

The converter was made by Phoenix Phase converters. I found a recent link that shows the 5HP model. I thought it was made by American rotary, but I guess I just remembered the name.

http://cgi.ebay.com/5-HP-Rotary-Pha...41952QQcmdZViewItemQQ_trksidZp1742.m153.l1262

The only instructions were a wiring diagram, that was it. Also, the Cap was epoxied into the box where I couldn't read the label. But yes, it was a retail purchased model.

If your idler motor is a dual voltage motor I suspect it is improperly wired with not all phases for the same voltage or one or more coils reversed. Seems fairly likely if it was disconnected for the move.

Don Young

After seeing that your converter is a commercial unit with integral motor it seems much less likely that there is a motor wiring problem. The only other thought I have is that there might be a starting-only capacitor which is remaining in the circuit due to a relay sticking closed. Excessive running capacitance will cause high voltage on the generated leg.

Don Young

There are no relays in the unit junction box that I can see. I doubt there is room for one in the motor.

I'm beginning to wonder if I should just get a panel and remove the motor from what I have, and re-use it.

I have the 30HP unit as well, but I don't want to set it up just to power the machines I have. That would be a huge waste of power. At least since I sold the machine that I had intended it for.

Your DMM is just fine. What you are measuring is meaningless with the unit unloaded.

Just wait until you can measure the voltage with the unit loaded. It is then very simple to balance the output voltage with a capacitor if required.

Check out some of the threads in this forum on building your own balanced RPC.