Pony motor RPC starting question

[Barncat]

I’ve built a pony start Rotary phase converter. Is there a way to test which way the 3 phase motor wants to spin before firing it up to make sure the two motor directions don’t work against each other? I know the direction can be changed by reversing two leads, but would like to have both motors spinning correctly before starting it.

 

[Karl_T]

Like Clint Eastwood as dirty harry said,"do you feel lucky?"

Only way I know is leave the belt real loose and try it.

 

[markba633csi]

I believe it doesn't matter, the pony motor sets the direction and the main motor will follow
On smaller systems with a single idler motor the start capacitor sets the direction, but in this case the pony motor serves that function
-M

 

[MikeInOr]

I believe it doesn't matter, the pony motor sets the direction and the main motor will follow
On smaller systems with a single idler motor the start capacitor sets the direction, but in this case the pony motor serves that function
-M

I am pretty sure Mark is correct. The two phases on the idler motor are 180 degrees apart so which ever direction it is started is the direction it will go. 3 phase legs are 120 degrees apart so the differential between all 3 legs is what determines the direction... and swapping 2 legs reverses the direction only with 3 phase.

 

[MrWhoopee]

Disconnect the pony motor from the 3 phase motor. Wrap a rope (or belt) around the shaft of the 3 phase motor, connect power and pull start the motor. I've known people who used this as the regular starting method.

 

[JimDawson]

I’ve built a pony start Rotary phase converter. Is there a way to test which way the 3 phase motor wants to spin before firing it up to make sure the two motor directions don’t work against each other? I know the direction can be changed by reversing two leads, but would like to have both motors spinning correctly before starting it.

I had the same question when I built mine. I tried it in both directions and there was no difference that I could see. I figured it would dim the lights and trip the breaker if it wasn't happy, but it seemed to be happy in either direction.

 

[benmychree]

I did the same as above, used a knife switch to start the pony motor then hit power to the 3 phase motor and shut off the pony motor; worked fine until I got the real 3 phase connected.

 

[Barncat]

Thanks everyone. I didn’t realize the 3 phase motor would follow whatever direction the pony set in motion. I was worried it would be going the wrong way and then grind to a halt when I hit power to it. Is there an order of operations for starting a 3 phase with a pony? My plan is to get it rotating then apply power to the 3 phase motor after the pony has it up to speed.

 

[JimDawson]

Is there an order of operations for starting a 3 phase with a pony? My plan is to get it rotating then apply power to the 3 phase motor after the pony has it up to speed.

That is the proper sequence.

 

[MrWhoopee]

Thanks everyone. I didn’t realize the 3 phase motor would follow whatever direction the pony set in motion. I was worried it would be going the wrong way and then grind to a halt when I hit power to it. Is there an order of operations for starting a 3 phase with a pony? My plan is to get it rotating then apply power to the 3 phase motor after the pony has it up to speed.

It's not even necessary to get it up to speed, just spinning is enough. As I said, I knew a guy who started his with a belt (the kind you wear) every morning. Just a 3 phase motor and a disconnect. Wrap the belt around the shaft, pull the belt and flip the disconnect on.