Issues with 3 phase.

[graduate_owner]

I have a number of questions regarding single to 3 phase converting, and I'm hoping someone on the forum may be able to help.
First -I have a 3 hp static converter which works OK but I know these are not ideal. I also have a spare 3 HP 3 phase motor and my question is, can I connect the motor to the converter and will this effectively make it a rotary converter? If so, should the spare motor be connected star or delta? My instincts tell me star, and it suggests star in the book I have. ( be prepared for disappointment if you use delta, it says). BUT I also have a rotary converter (trying to repair it) and the motor on that is connected delta, and the instructions say it should be delta. So I am a bit confused.

Second - I use an inverter to give me variable speed on my lathe etc. Using motors connected in delta, 240volt. I tried connecting it to a 3 phase 1 HP Canning polisher (rated 380 - 415 volt) and expected a loss of power and torque. What happened though was the speed increased from zero as I turned the speed control pot on this inverter, then reduced down to zero as I continued turning the pot. The reading on the inverter display also went from zero up to about half way then back to zero. That has never happened on any other motor. Does anyone have any ideas? I assume the Canning motor is an induction motor but I don't know.

K

 

[Myfordman]

To add a motor to a static converter to make it a rotary type the voltages must match.
Assuming you converter is a 415v output then the motor should be too. Again assuming the motor plate says 240/415, then you want to connect it in star to the higher of the two operating voltages.
Post a photo of the motor plate if you are not sure.

Re your second problem, it is not possible for me to say what is happening with certainty. I would agree with your expectations in your second sentence.
I also think it is very likely that the motor is an induction motor.
Do you know the canning motor to be OK? is the resistance between each of the three terminals equal? if not this suggests a faulty motor which the inverter could sense and act to limit damage to itself.

 

[graduate_owner]

Hi again Myfordman,
just an update - the 3HP motor works fine on my static converter, connected in star mode, and starts up my 3hp lathe fine - even in top speed, which the static on it's own would not do. It seems to work just as well whether the static is switched into 1, 2, or 3 hp. It also runs the polisher so I don't need to use the inverter on that. I was hoping to use the polisher as a grinder too, but the speed is too high so it will stay as a polisher.
Thanks for te advice, again

K