Pony drive RPC help for Monarch CK

Just built a Rotary phase converter with a pony motor start. I'm having issues blowing fuses when I attempt to spin the motor up to speed. Assuming my wiring is correct, would pulley size create the issue? My 3 phase motor pulley is a 6" and my pony motor pulley is a 3". I feel that this may be causing a excessive draw on my power system causing the blown fuses. My fuses and switch are all 60 amp rated so I assume these wouldn't be an issue. Do I need to get the generator motor closer to running RPM (1750)before kicking in my 220V 1 phase power?

I'm doing a pony motor due to my limited electrical experience, so please dumb down your replies.

Generator:
10 hp Baldor
60 amp
1750 Rpm

Pony:
3/4 hp
1750 rpm

Welder6131 - not sure exactly what you are quoting when you say 60 amp on 10 HP motor - there are several possible amp ratings on the motor label.
In general a 10 HP motor (3 phase) using 230/240 Volt should be around 25-30 amps current draw (full load current) - BUT the inrush current being much higher (3-6 times higher) which might indicated by label such as LRA (Locked Motor Amperage)..
Your claim to 60 amps makes me wonder if that is for the (10 HP) motor being connected using 120 Volts (although that is a rare and unusual setup for 10 HP motor - and would also not be 3-phase motor)
Also you have a 2:1 ratio on your pulley combination so that the pony motor will get the RPC motor only up to half full speed.
To speculate - you are drawing too many amps as 'inrush" or starting current on the RPC motor - the pony motor is not spinning it fast enough...although if you have fuses that are 'slow-blow' you should still be OK for the short time the inrush current exceeds the fuse rating...
Need to know what the 60 amp rating refers to - something is not exactly making sense regarding 10 HP vs 240 Volt vs 60 amps as in your OP - one of those numbers does not seem right - unless the 60 amps is LRA (inrush current) but then that too seems a little low for 10 HP motor unless you have a newer and efficient motor..
Post a picture of the RPC motor nameplate - or list the #s with the labels on that plate - would help..
Short answer: yes on the pulleys -first thing to try; since pony motor and RPC motor are same rated speed - you want same size pulleys on each. Also with your current 2:1 pulley ratio unless you are disengaging the pony motor the RPC will be trying to drive pony at 2x its rated speed.
Edit: FMOI - I went and looked at a couple of 10 HP 3 phase motors I have and none of state LRA amps (Locked Rotor Amps) but simply 'amps' which will be the "Full load Amps". My 10 HP motors range from 24 to 27 amps if configured for 240 volts (as fits the 'rule of thumb': 2.5 amps per horsepower for 240 volt 3 phase motors). So if your nameplate states amps are 60...Are you sure that is a 10 HP motor (not more like a 20 HorsePower)?...The current to start that 60 (full load amps) amp will go well over 100 amps - even if you spin it fast enough with the pony motor (with a bigger pulley) - you are still on the brink of blowing your fuses when use the RPC motor to drive your lathe..

Spin it up fully

Hi

I had a similar issue years ago. Get the 10HP up to top speed, release the pony motor load (slacken the belt) and turn it off quickly and then apply power the the 10HP while it is spinning. You may need to change the pulley to get it to 1750 RPM to give you a bit of time to release and power it up.

The pony motor must spin the idler motor up to full speed. If you have a 1750 idler then it needs to be spun up to 1750 rpm. Your 60 amp disconnect and fusing are appropriate for a 10 hp idler RPC. I hope you sized the wiring to carry to carry at least as much amperage as the fuses are rated for.

If this is just an idler with no run capacitors, expect to start a 5 hp load motor, and run a little more. If it has run caps on both generated phases then you can expect to start a 7.5 hp load motor and run up to 10 hp total load.


Operation: to start,
power on to pony motor
when up to full speed, say 5 to 10 seconds,
power off to pony motor and power on to idler motor.
It should start easily and not even dim the lights when starting.

to stop, just turn power off to the idler motor and let it coast to a stop.

Thank you all for the replies, I was incorrect in my amp rating. The motor amp ranges depending on how its wired are 30-28 / 14. So this would put me around the 30 amp range....meaning my 60 amp switches / fuses are more than adequate.

My first course of action will be to change pulley's to the same sizes and trouble shoot from there.

No I'm not using any capacitors, however the largest motor I will run at a given time will be 3 hp on the old Monarch CK. I will update my findings as they happen, thanks again!

Josh

Hi Josh,

As others have already stated, you need to have the same diameter pulleys on the pony and idler motors and you need to make sure that you are using "slow-blow" or time delay fuses.

Remember that the fuses are there to protect the wiring, not the load. With 60A fuses you need at least #8 wire and you may need #4 wire, depending on the length and type of wire you're using.

What kind of switch are you using?

To protect the idler motor you need some sort of overload protection. You can use a manual motor starter with thermal overload protection that will not trip when the idler is starting but will trip if the motor draws over the preset current for very long. The overload protection device is similar to a common circuit breaker except that it can be set for the desired trip current and is designed to handle the high current inrush of a large motor. Without overload protection you are risking burning up the motor and maybe setting your shop on fire. Something like this will do the trick:
However, by the time you buy the overload switch and enclosure and pay shipping you're probably into it for about $75. It makes more sense to buy a real rotary phase converter panel to use with your idler motor. This get's you push-button starting, overload protection and run capacitors to help balance the current on the artificial phase. WNY Supply has one for $184 and they frequently offer free shipping: If you need to save some money you can buy a kit for $96: (I don't have any relationship with WNY.)

Cal

Another important point is that the 10hp idler motor cannot be trying to do a plug-reverse due to the "direction of rotation" that its wiring creates.

That will blow fuses.

The 10hp must attempt to continue in the same direction of rotation that the pony has applied.

I am in the midst of building a pony RPC too and now you have me thinking....slowly, but how does applying 1phase to a polyphase motor rotating at half speed cause it to perform a plug reverse? Or is it a matter of energize point vs phase angle timing?

matt_isserstedt said:

Another important point is that the 10hp idler motor cannot be trying to do a plug-reverse due to the "direction of rotation" that its wiring creates.

That will blow fuses.

The 10hp must attempt to continue in the same direction of rotation that the pony has applied.

Click to expand...

If there are no capacitors, the motor rotation is totally arbitrary. Different story with capacitors.

To the point from weedy64, its not about plugging, but that the rotor is not spinning fast enough to develop the needed counter EMF. The main motor is still in the locked rotor stage of startup. Go online and look at some starting current curves. The locked rotor condition is not materially affected until about 80% of running speed.

Tom