3 phase power and rotary phase converters

3 phase power and rotary phase converters · 01-11-2009, 01:06 PM

Say I have a 10 Horsepower motor on a planer and a rotary phase converter. The single phase power to the rotary phase converter is rated at and cabled to handle 100 amps.

Everytime you try to start the motor, it somewhat comes up to speed and then it trips the 100 amp breaker. If you take the belts off the motor starts fine. The planer head spins freely. If you put the belts on to the head it trips the breaker.

Checking the wiring it was a single phase leg, manufactured leg, and a single phase leg.

Switching it around so that the single phase legs come first and the manufactured leg comes last makes it work properly.

So I assume the single phase legs have to come first, but why? If there were true 3 phase power from the power company I don't think this would be an issue would it?

Do the single phase legs have to come first and the manufactured leg to come last in order for the motor to reach full power? Why?

DaveD · 01-11-2009, 01:59 PM

I'm fairly new to rotary phase converters but have successfully built (and troubleshot) one (10HP) to power a 5HP lathe.

I know this is a real stupid question but you do have the rotary phase converter up and spinning before turning on the equipment, right?

What size is the RPC motor? At least 15HP?

Swapping any two of the 3 phase legs on the planer is going to reverse the motor direction so I assume you did more than just swap two when you described your troubleshooting and 'moving' the 'wild' leg.

Here is what I have found when getting mine working.....

Any controls (like a 220v control transformer or coil) in the piece of equipment need to be on the two 'native' legs and not the 'wild' leg. The wild leg raises h e double ell with controls.

Other than the control statement above, the motor on the piece of equipment doesn't know its manufactured 3 phase.

The 3 voltages off of the phase converter (when it is running) need to be (if I remember correctly) within 10% of each other. Otherwise you have to play with the run capacitor values across the legs to get it balanced out.

The RPC motor needs to be bigger than the machine motor. In my case it was debatable if a 7.5 HP RPC would run the 5HP gear head lathe (startup load) so I went with a 10HP motor on the RPC.

I still had to play with the start capacitors because the 1st time I tried to spin up the RPC all it did was spin slowly, get REAL warm, and 'growl' (all in a period of about 5 seconds times 3 tries), Now that I got the right start caps on it (about 100 MFD/HP) it will come up to full RPM almost instantly (less than a second).

My RPC motor is 1800 RPM but a 3600 RPM (or whatever) will work just as well. My understanding is the higher RPM motor takes more current to start (run?) but I can't remember why.

Woodman2k · 01-11-2009, 02:48 PM

Travis,
I believe it has to do with the phase angles of the native legs opposed to the manufactured leg.I have also read that based on the rated load the converter could need to be rated at a factor of 3 if the load is sufficient enough.By the way,a high speed motor will produce more appropiate phase angles but a slow speed motor will start easier.Your idler/inverter motor should be running at or near full speed before you try to start the load motor.You seem to be heading in the right direction.
Greg

Travis Porter · 01-11-2009, 04:05 PM

The phase converter in question is a Kay Phasemaster rated to start a 20 horsepower motor.

David, there are only two stupid questions in my book. The one unasked, and the one you ask over when you got the answer and didn't listen the first time.

Yes, the phase converter was on, up to full speed and running normally. I have seen the issue you speak of with using the manufactured leg on electronics, transformers and such first hand. When I was doing the testing, I moved the wires from the output side of the contactor for the main motor because if I had moved them where the power comes into the electrical panel for the planer it would not have been pretty with the electronics.

Greg, I think you may be on to something with the phase angles. What is wierd though is why would it start and run normally without the pulleys to the planer head....

cpowell · 01-11-2009, 05:50 PM

I'm not an RPC expert but know a little about 3-phase power.The output from the RPC should be 3-phase. 1-2, 2-3, and 3-1 may differ slightly in voltage magnitude. If you loosened 2 wires and reversed the connection it will reverse motor rotation.

Not knowing much about the load (planer head) would it require more power to run "backwards"? Obviously the planer head would need to be accelerated to speed along with the planer motor so the connected load would require more power than motor alone.

A few questions to ponder?

Is the planer motor in good shape - no problems? I mean, did the planer work for a while and then beging giving you trouble?

Is the feed wiring large enough for motor inrush?

Have you talked with tech support at Kay?

Once you managed to get the planer running how did it work when loaded (planing stock)?

I would like to get a 3-phase motor and some starters/caps and build an RPC one day.

Chuck

Travis Porter · 01-11-2009, 06:30 PM

It' isn't mine, but Kay has been called as well as Grizzly. Grizzly said that they have never seen one of these motors go bad. Kay said (before rearranging the L1,L2, M1 that the convertor was more than large enough to handle the machine. Wiring exceeds spec. Current and voltage have been validated to be sufficient by the power company.

Labeling the phases as L1, L2, and M1 where M1 is manufactured, everything was laid out as L1, M1, and L2 as specified in the manual to protect the electronics and transformers. It would not start with the head hooked up. Changing it to L1, L2 and M1 worked but it ran backwards so it was finally changed to L2, L1 and M1. Haven't planed any wood yet as the bolts for belt tension need to be re-tapped (cross threaded), but it will be.

Travis Porter · 01-11-2009, 08:02 PM

I stand corrected. It still doesn't work right. Time to check voltages, current, etc.

DaveD · 01-11-2009, 08:06 PM

I went and looked at the KAY site and don't like how they say to wire the two incoming legs directly (possibly thru a 3 phase disconnect) from a safety standpoint.

If the incoming power blips and drops out the phase converter then you are going to have voltage at the machine that you may not expect (when the power comes back on). Or when the power comes back on the whole thing is going to reatart on its own.

I have a panel from WNY Supply that has a contactor in it so if the power drops the contactor automatically drops and it won't run on its own when power is restored. You have to hit the start button on the converter panel to get it started again.

Even though you have it running I'd suggest that you measure the voltage on all 3 legs with the converter running and the planer offf and then again with the planer running. If you can measure running current that would help to understand if its running ok too.

I'm curious as to what is in the KAY phase converter control box. Have you looked inside it? It should have have some start and run capacitors and a contactor and maybe a time delay relay.

How do you start the KAY converter? On my WNY panel you hit a push button that pulls in (through a relay) the start capacitors and then the time delay relay automatically disables the start button and drops out the start capacitors after about a second. Its set up that way so the start capacitors can't stay energized too long.

Saw you didn't have it running yet. Be sure the planer motor is wired for 220 and not 440. There should be a wiring diagram on the motor frame or on/in the little wiring box on the planar motor. If the RPC is new to you and this is the first setup then check the wiring on the RPC idler also.

Travis Porter · 01-11-2009, 08:20 PM

For this one, he has a 220V switch set up to turn power on and off to the converter. On mine (which is a Kay), I have a rotary on/off switch built into it. I have looked into it, and it does have capacitors, some buss type fuses, and a couple of other things. I haven't looked into it in great detail before, but after reading your post and reading up on the internet some it is starting to make some sense.

Correct me if I am wrong, as all of this is my opinion after what I have been reading. All advice and comments are appreciated, as I am always wanting to learn more.

A rotary phase converter is a 3 phase motor (preferably a wye type not a delta type) that has capacitors for starting and capacitors for running. The start capacitors are normally activated with a time delay relay that drops them out after start up. The run capacitors should be the electrolytic type as they will hold up better.

Playing with this guys stuff and reading through documentation I am beginning to believe their is either an issue with the size of wiring somewhere, the run capacitors, or the 3 phase motor the convertor is built upon. If the motor on the planer starts up without the planer head on it, and it worked before he bought it (saw it crank up) it tells me the converter he bought is acting up. Since it is a 3 phase motor as well, it is probably the capacitors (if the wiring to the planer is good).

It seems like there is really very little to go wrong with a 3 phase motor. It either works or it doesn't.

One thing that bothers me about all electrical stuff is this. You get told and you read you need to run this big wire to handle the load to a device. You open the covers and get into it and there you see 16 gauge, 18 gauge etc. Why do you have to run such big solid wire to a motor and then everything from the connection point is tiny?

cpowell · 01-11-2009, 08:24 PM

Originally Posted by Travis Porter

It' isn't mine, but Kay has been called as well as Grizzly. Grizzly said that they have never seen one of these motors go bad. Kay said (before rearranging the L1,L2, M1 that the convertor was more than large enough to handle the machine. Wiring exceeds spec. Current and voltage have been validated to be sufficient by the power company.

Labeling the phases as L1, L2, and M1 where M1 is manufactured, everything was laid out as L1, M1, and L2 as specified in the manual to protect the electronics and transformers. It would not start with the head hooked up. Changing it to L1, L2 and M1 worked but it ran backwards so it was finally changed to L2, L1 and M1. Haven't planed any wood yet as the bolts for belt tension need to be re-tapped (cross threaded), but it will be.

Check out fundamentals. I would check all 3 line voltages from the RPC - with the planer unloaded (at idle condition) and then loaded. I don't think ground references mean anything here, a motor should generate delta voltages, just measure between lines L1-L2, L2-L3, and L1-L3. I would measure both RPC output AND at the load side of the motor contactor. I hope that if you have a flaky cap then one of the voltage magnitudes will stand out. See if you can get a clamp on ammeter and check motor amps to see that they are balanced. They won't be identical but should be close. You're looking for something that jumps out at you.

As you expected, swapping wires between motor contactor and motor should have no effect. None. (except that it will change motor rotation).

Set belt tension and run the planer and post results. If the planer eats wood after you modified wiring them you don't have a problem.

IF this is the same planer you posted with problems earlier I would consider this as STRIKE 3... you should sell it to me for 150 dollars. 'nuff said.

Chuck

scsmith42 · 01-11-2009, 08:33 PM

Originally Posted by DaveD

I went and looked at the KAY site and don't like how they say to wire the two incoming legs directly (possibly thru a 3 phase disconnect) from a safety standpoint.

If the incoming power blips and drops out the phase converter then you are going to have voltage at the machine that you may not expect (when the power comes back on). Or when the power comes back on the whole thing is going to reatart on its own.

Dave, I concur that it's a good idea for your equipment not to restart automatically in the event of a power loss, but if the piece of equipment operating off of the phase converter had a magnetic start switch, wouldn't it shut off the machine automatically in the event that two of the three legs were lost, and thus prevent it from restarting?

Also, if you're running on three phase line power you will have voltage at the equipment when the power is on... and if the power blips you will still have voltage at the equipment when the power comes back on. What's the difference between power at the equipment through a phase converter versus power at the equipment via line power? In order to prevent the equipment from restarting after a power loss a magnetic start switch should be used, regardless of single phase versus three phase, right?

Scott

Travis Porter · 01-11-2009, 08:38 PM

Originally Posted by cpowell

IF this is the same planer you posted with problems earlier I would consider this as STRIKE 3... you should sell it to me for 150 dollars. 'nuff said.

Chuck

No it isn't!!!

It is a friends planer, and it is much bigger than my PM.

scsmith42 · 01-11-2009, 09:10 PM

Travis, I recently had a similar discussion with an electrician friend of mine (Gene Ezzell) concerning the power in my new shop. Gene is a licensed electrician and specializes in generator installation and maintenance (some pretty large stuff for Ft. Bragg and large commercial farms down east).

Based upon some of his comments to me, I don't find anything unusual in what your friend is experiencing, and here is why.

Gene's formula for sizing a main breaker is FLA x 1.2 x 2, and he stated that in some instances even this is not great enough (such as if there is a large rotary mass attached to the electric motor). We had some extensive discussions about the mass of the planer head and how much it could affect start up amperage (same issue concerning the sizing of the main breaker in the box).

According to my pocket reference, typical FLA for a 10HP 220V 3-phase motor is 27. Running this through Gene's formula results in a start up amp surge load of 65 amps.

In addition, you have the draw on the phase converter, plus whatever else is running in the shop. Presuming that your phase converter is greater than 10HP (which it would have to be in order to start the 10HP load), you may be exceeding the capacity of the 100A breaker. For instance, if the phase converter is 15hp, the FLA is 38 amps, so you're already over 100A total. AND, in essence a phase converter is acting like a 240V single phase motor, so your actuall FLA may be greater than 38 if it is measured as a 15hp 240V motor. Even though the phase converter is already running, it will see a tremendous load from the start up current demanded from the third leg that it's producing, and I'll bet that this is close to the FLA for the converter.

If it were me, I'd put a larger main breaker in the box and see if that solves the problem.

Scott

Travis Porter · 01-11-2009, 11:41 PM

Your comments are almost mind boggling. I'm not arguing your point, it is just hard to believe..... I see your logic, and it does make sense..... That is a LOT of amperage.... It did take the thing almost a minute to start when we were getting it to run, but geez.... A 100 amps insufficient? I only have a 100 amps in my entire shop and I run my 10 HP wide belt with it, but then again, it isn't like turning a planer head and my phase converter is smaller. I think his is more like a 20 or 25 hp unit.....

Mind boggling, but a very valid suggestion.

toolman · 01-12-2009, 12:44 AM

Hey Travis

I had 2 rotary phase converter 1 - 10 HP and 1 - 20 HP. I had a 50 Amp 3-phase panel box. From the Main Box I ran a 220 single phase line to the rotary phase converter and a 220 single phase line to the 3 phase box T1 and T3. Then ran the hot wire from the rotary phase converter to the 3 phase box T2 to make it 3 phase..

My 10 hp rotary phase converter would start up to a 10 hp motor and would run up to a total of 20 hp (ie: 10 ph, 1 hp, 5 hp, and 4 hp.)

Rotary phase converter are rated in Horsepower you can not start a 20 HP motor with a 5 HP rotary phase converter.

In your case you need no less than a 10 HP Rotary phase converter, if your planer has a 10 HP motor..

I ran a machine shop with 2 mill - 1 1/2 hp ea, 2 lathe -1 -5 hp 1 -10 hp and a grinder - 2 hp with my 10 hp Rotary phase converter. Then I add more machine I replaced my 10 with a 20 hp. Then 3 year later I add a CNC lathe so I had the power Co. to run 3 phase line to the shop.

As for as the placing of the wires the manufactured leg can go in T1 T2 or T3 but you will need to check rotation.

1. You will need 2 220 hot wires with ground (3 wires) going to the Rotary phase converter.
2. You will need 2 220 hot wires with ground (3 wires) going to your sub panel.
3. You will run 1 hot wire from the Rotary phase converter to your sub panel.
Now you have 3 phase..