Rotary phase converter versus trying to run a VMC straight from single phase



I friggin give up....
WHY, WHY, WHY do you need a pony motor for a 20 horsepower idler????
A few thousand Mfd worth of starter caps, and it will SNAP to full RPM in a Fraction of a second.. WHY make it so extra complicated?
Hi Half
Dont give up so quickly. You can learn about this stuff if you take just a little time to think about it.
Some people just like the use of pony motors. They dont consider them so extra complicated.
Some people have difficulty getting their capacitor switches to live due to contact arcing.
Some guys even blow up capacitors due to inappropriate On time.
Sometimes capacitors are not reliable.
Spinning up rotary converters is kind of a presonal preferance thing. I use capacitors and a solid state switch for my 3 phase motor spin up.
Jerry
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My own answer to the "motor too big, need easy starting" problem was to use two idlers, to be started in sequence. Mine are 10 and 7.5 HP.
i
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http://www.gromax-usa.com/supplies/converter/parallel.gif
Ad-nauseum...
--


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Yes. Mine was slightly more clever than this.
1) I used two contactors instead of 3. Which worked well, they just needed to be wired differently.
2) The first motor had a capacitor on legs 1-3. It assisted with starting, but resulted in unbalanced 3 phase.
3) The second motor had a capacitor between legs 2-3. When it was connected to the network, the capacitors became equal between legs 1-3 and 2-3. That resulted in a much more balanced 3 phase.
i
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On Tue, 19 Feb 2008 17:27:55 -0800 (PST), rpseguin

It's NOT true. I originally had my 20hp converter hooked up to a 60amp breaker. Never had a problem.
I changed to a 100amp breaker when I hooked up the second converter. Both converters, the 20hp *and* a 15hp, running off the same 100amp breaker. Both converters ran daily, for 4 years. Never even saw the lights flicker.
Matt
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Ok. That's all good news that I've seen from the group regarding breakers not popping. I'm looking for run caps and start caps now to get this thing going.
Thanks!
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On Wed, 20 Feb 2008 16:02:46 -0800 (PST), rpseguin

You can always contact Reed @ Convert-A-Phase.
http://www.convertaphase.com/contact.htm
He's here in Escondido. I bought a 20hp box from him. Start caps, run caps, all set up and ready to go. Bought a used 100apm disconnect from him, and hooked up my own 20hp motor. Even got him to come over to the house and tune it for me.
IIRC, the control box was just under $500, and maybe another $100 for the disconnect. But that was 11 years ago.
It might be cheaper to build it from scratch, but the peace of mind in knowing that you have all the right caps, and everything is connected properly, and all you have to do is run your 220v to the box, is worth every penny you'll spend on that control box, IMO.
Also bought the 15hp box from Reed and added my own disconnect and motor. I mounted both of them on wooden frames and hooked them up to breaker boxes, and had breakers for each machine. The 20hp ran 4 cam operated Swiss screw machines, a CNC Gang Tool lathe, a tool grinder, a bridgeport, and an engine lathe. The 15hp only ran a Tornos 5-axis CNC Swiss. You'll notice voltages increasing and decreasing as machines are turned on & off. I didn't want to take any chances with the Tornos.
Warning! DON'T mount them on wooden frames! At least don't mount the motor on wood. I made the base out of 4x4's, with a double thickness of 3/4 plywood and bolted the motor to it. Big mistake! Those things make a constant humm anyway, but the wood was the prefect acoustic base it needed, and it amplified the hummmmmmm. Drove me nuts!
Matt
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Hi Matt,

That made me laugh. I mounted one of our home made cap-style 10hp rotary converters on rubber and it made it's hummmmm about 10 times louder too. It is back on the concrete and barely audible again.
Dave
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On Thu, 21 Feb 2008 09:07:06 -0800 (PST), "Dave, I can't do that"

Really!? How about that. I would have thought the rubber would help. I may wind up back in the garage. Still have the converters and was planning on making a heavy steel frame, with rubber feet, or put it on felt pads.
A friend has a 10hp that is mounted on two pieces of steel channel. The control box is attached to the rail/motor, and it just sits on the floor. The disconnect and breaker panel are mounted to the wall. It's really quiet.
I kind of liked having it all together in one unit. Makes it easy to move around when needed. Perhaps I should reconsider.
But then, I've also thought....... If I have to do it again (move back to the garage), the converters may wind up out in the shed:-)
Matt
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The hummmm noise is mostly due to field imbalances in the converter. In other words, they are an electric problem. My old converter was making a lot of hummm, but on my new one, all noise is from bearings, fans etc and is all high frequency. No hummm. That's because it is electrically balanced.
i
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On Wed, 20 Feb 2008 21:15:34 GMT, Matt Stawicki

You obviously had motor rated breakers.
Gunner
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The Pre-Meltdown Kid wrote:

The Cedarburg converters are like this, they are essentially just a starting capacitor and a relay to switch it in when needed. They are horrible pieces of junk, barely adequate for a water pump, I'd hate to see you use one on a CNC machine. Also, some motors run well on these (Bridgeport J-head motors, for instance) and some run hot, have little torque or otherwise misbehave.
Jon
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