Film-Tech Forum ARCHIVE: Converting Christie P35GPS to VFD motor drive

This is topic Converting Christie P35GPS to VFD motor drive in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Michael Trudell (Member # 3344) on 12-15-2014, 05:38 PM:

I know that Steve Guttag would have some great information here.

I am doing the initial research to change the stock capacitor Bodine motor to a Bodine 3 phase, inverter motor. Some questions:

1) The Bodine 48R motor that comes with the projector has a 1/2" shaft, but the stock 48R (all flavors, 3 phase included) has a 5/8" shaft. Additionally, the forward mounting face on the motor has additional helicoil mounts for the projector mount. I have a couple of choices here. I could: a) take the drive pulley and flywheel to the machine shop (hopefully they'll come back true) and drill new mount holes on the motor mount or, b) could I take the existing rotor and forward mount face, leave it on the projector and replace the 48R capacitor motor case with a 3 phase 48R motor case/stator?

2) Should I look for a 1/2 HP or 1 HP rated inverter? I've seen some different recommendations.

3) Does anyone know if the drive belts/pulleys are Gates pulleys/belts? How could I order from them? I haven't been able to readily see any sales outlet.

4) What is the difference between a stock 3 phase motor and an "inverter duty 3 phase motor"? The only difference I can see is "inverter grade magnet wire and Class F insulation." Can non-inverter duty 3 phase motors be used with an inverter? Maybe someone has a story of some kind regarding their experiences.

Thanks in advance, have great holidays everyone!

Mike

Posted by Will Kutler (Member # 770) on 12-16-2014, 10:25 PM:

Why would you even bother with that pile of junk?

Posted by Brad Miller (Member # 2) on 12-16-2014, 10:28 PM:

Mike has a "The Jim's" Christie projector, not a "Bevan" Christie projector. That vintage was quite amazing machines.

Posted by David Buckley (Member # 2600) on 12-16-2014, 10:48 PM:

quote: Michael Trudell
What is the difference between a stock 3 phase motor and an "inverter duty 3 phase motor"?

Motors and motor control are probably my weakest area of electrical knowledge, so I'm lightyears from an expert on them, but I do know a couple of tidbits.

The first is that running a motor off a VFD allows the motor to deliver full torque whilst running at less than the design RPM. Thus the motor's cooling fan is running slowly too, and thus is less able to remove the heat. For this reason inverter duty motors have more fan capacity, and can often run hotter than stock motors.

The other is that the waveform of the power supplied from the VFD is much more like a square wave than a sine wave, and the PWM frequency is vastly above the nominal suply frequency, and this tends to stress insulation.

So whereas any three phase motor should be able to operate off a VFD, under stressy conditions the motor will have a harder life.

Posted by Michael Trudell (Member # 3344) on 12-16-2014, 11:00 PM:

Thanks David for your response. From what I gathered from other's experiences, it seemed that early versions of the Bodine motors had a rep for running hot. I figured there had to be some extra meat somewhere for PWM operation.

I actually have a lot of experience with brushless DC motors, but only a little with AC 3 phase motors.

Looking back on earlier posts, it appeared that a 1 HP rated VFD should meet the acceleration demand without burning up.

I have been very pleased with the performance of the new Christies. I have seen them operate in person before they came to me and they have wonderful picture stability. I love how the motor swings out easily and the straightforward engineering. My previous experience has been with Norelco's, JJ's and (way earlier) Simplexes.

Posted by David Buckley (Member # 2600) on 12-17-2014, 12:30 AM:

quote: Michael Trudell
I actually have a lot of experience with brushless DC motors, but only a little with AC 3 phase motors.

As you've probably noticed, these two technologes have a lot in common!

quote: Michael Trudell
Looking back on earlier posts, it appeared that a 1 HP rated VFD should meet the acceleration demand without burning up.

Given that projectors (in my limited experience) have fractional HP motors, I'd have thought a VFD rated at 1HP would be fine.

The other thing that comes to mind is motor voltage; again, not my area of expertise, but theres something ringing a bell about motor voltage and compatibility; a common setup for small motors is a three phase motor and a single phase supplied VFD, which requires the three phase motor to be rated to operate at the single phase voltage, not the three phase voltage. And that some three phase motors are wired delta and can be rewired star so they can run on single phase voltage over three phases... I may be blubbering a bit here!