rotary phase converter

According to harry :

It sounds to me as though the unloader is not working, so the motor has to start in the face of a major load. Normally, when the motor shuts off, the unloader lets the air in the compressor cylinders out, so it can start more easily, and then it lets the pressure build once the compressor is running to fill the tank.

Last I heard, he had moved out to somewhere on this (the East) coast, but he has not posted very much at all.

Check out the unloader for your compressor. I'll bet that is the problem.

Do you have a manual for it? If not, try contacting the manufacturer, and that might help to trace down where the unloader is and what it looks like.

Good Luck, DoN.

So, you have trouble starting your compressor even when both idlers are running at full speed? I am a little confused as to what is actually happening, you are a little vague about time delay relays.

i

Harry, Here are steps I took to address the same issue;

1. Install a time delay relay.
2. Install 2 solenoid valves. One to operate (open) the unloaders and the other to dump all air pressure between the 2 stages, assuming that it is a 2 stage unit.
3. Operate it off 480V by using a transformer to boost voltage.
4. Wrap heat tape around the base of the cylinders to warm them in cold weather.

Bob

If you are running off a motor used as a phase converter, your motor on your compressor has had a big drop in horsepower from the poor quality of your 3 phase power. Probably most of your problem results from this. When I put an amp-probe around my three wires from my home-made

3 phase to my milling machine, I find that the generated 3rd leg has no current in it, and the other two legs are carrying all the current that is running the motor.The home made 3rd leg also has noticeably lower voltage than the 220 volts input from the power company running the rotary converter and mill. I think you get just enough 3rd phase from a motor type converter to start things, but the motors are really running single phase.

I.e., I am cynical that you will ever be happy with the results you are going to get with a rotary converter and something as hard to run as an air compressor. Air compressors are serious loads. I bet a 10 horsepower single phase motor would cost 450 bucks new, but you might get lucky at your local scrap yards. If I were in your shoes, I would change the pully on my motor to get the compressor to run slower, and settle for a compressor that is effectively 5 horsepower, not 10.

brownnsharp

If you are running off a motor used as a phase converter, your motor on your compressor has had a big drop in horsepower from the poor quality of your 3 phase power. Probably most of your problem results from this. When I put an amp-probe around my three wires from my home-made

3 phase to my milling machine, I find that the generated 3rd leg has no current in it, and the other two legs are carrying all the current that is running the motor.The home made 3rd leg also has noticeably lower voltage than the 220 volts input from the power company running the rotary converter and mill. I think you get just enough 3rd phase from a motor type converter to start things, but the motors are really running single phase.

I.e., I am cynical that you will ever be happy with the results you are going to get with a rotary converter and something as hard to run as an air compressor. Air compressors are serious loads. I bet a 10 horsepower single phase motor would cost 450 bucks new, but you might get lucky at your local scrap yards. If I were in your shoes, I would change the pully on my motor to get the compressor to run slower, and settle for a compressor that is effectively 5 horsepower, not 10.

brownnsharp

Hi Brownsharp

When you were measuring current the wires from the Rotary Converter to the Load Motor there would have been current in the "generated leg" if the units were wired correctly and were functioning properly. A properly sized Idler/Load rotary converter system will function in a manner indistinguishable from having a power company 3 phase input when the load motor is loaded to as much as 1/2 its name plate rated power. Even when the tool motor is loaded to its full name plate rating the tool motor functions very much the same as with power company 3 phase when the Idler is much bigger than the tool motor. With a rotary converter, current does flow in the wire connecting the generated leg of the idler to the tool motor, when the tool motor is loaded.

Jerry

Interesting...I respond at 9:55 pm Wed pm. Jerry responds to me at

10:42 Wed pm. When I look at the conversations at 6:19 AM on Thursday, I find my message from Tuesday is displayed...I have no idea how that could happen...

I am beginning to wonder if I should try another motor on my rotary converter. I would like more feedback from people using these converters about voltages developed on the generated leg.

brownnsharp.

I have a factory built rotary pahse converter that is based on a 15 HP motor. The generated leg runs a little high, not low. Two of the machines I run from this are CNC lathes with 10 HP DC spindles. The Randtronics Dc motor drive and the Fanuc 5T CNC controls are both well known to be sensitive to uneven 3 phase power. They shut down to protect themselves when there is too much difference in voltage between any two legs or if the voltage drops or rises too much. I think the threshold is 5%. I have used these machines with utility supplied power and they have shut down due to power fluctuations when other machines did not. Anyway, both lathes run fine from my RPC. I built another one for a friend to run his auto lift. I had to make it so that the generated leg ran high when idling in order to have the voltage balanced when under load. It's based on a 5 HP motor and drives a 3 HP motor. When there is a truck on the lift it will still raise it from a loaded start. However, because of wear in the lift mechanism there are a couple spots that it won't start from. If lowered an inch it will go through these spots because it's already moving. I checked the voltage when trying to start the motor at these spots and it sags enough that I'm thinking about adding a little capacitance. If you search RCM you will find plenty of good info about balancing an RPC. ERS

Hi Brownsharp

Your motor may be Ok. As I have understood your data, your voltages are about the same as what I experienced. My experience indicates that adding the proper capacitors from both legs of the power company's 220 lines to the generated leg of the idler (tuning) can increase the voltage from neutral (Y center) to the generated leg. That "adding capacitors" to tune the idler also increases the current on the generated leg when the tool motor is unloaded.

My data indicate to me that an idler will function better when *spinning up* a tool motor if the idler is tuned. A bigger idler will also improve the rotary converter's ability to spin up the tool motor.

Jerry

later i start the second rpc. 6sec later i start the compressor

what kind of valve ,how did you plumb it on the discharge pipe ,where did you get it , do you control it with a time delay relay,and i will still need to solve my voltage /amperage problem thanks harry Operate it off 480V by using a transformer to boost voltage.