[How do I?] Another Rotary Phase Converter Question

No 3 phase power out your way Jim? 50 amps man that's not a lot to work with.
 
Smithdoor said:
A 50 amp 240 v will only run a 5 HP motor
I have had a simple single to three phase converter for over 30 years works grated
I was only a 1725 motor 3 hp and use a 3/4 single phase motor for starting the main motor and helping on starting motors up to 10 hp

Dave
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Hey Dave,
your statement about a 50 amp service running only a 5 hp motor, simply is not true.
I have a 7.5 hp RPC that is wired to 50 amp single phase service that starts and runs unloaded 10 hp motors without tripping the breaker.
that is twice the capacity you stated.
 
John, you raise a good point about not switching all of the motors off. I wonder if adding a 1/2 hp motor to the mix that always runs, as an idler, would be the key. Hmmmmm.
 
coolidge said:
No 3 phase power out your way Jim? 50 amps man that's not a lot to work with.
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I have 3 phase at the street, but I just don't want to pay to have it brought in. And then there is the permitting issues, would probably cost more than the service. I really don't want any inspectors around here for a number of other factors. My limitation is the wiring to the shop, I could pull in a 100 amp, single phase wiring. I have enough power at the distribution panel.
 
JimDawson said:
In my OP I noted above I have a DoAll grinder that is wired for 480V. The question: Has anyone actually tried to connect a 240V output VFD to a 3 phase transformer to produce 480V, 3 phase? I thought I would ask before I let all of the magic smoke out of a 5HP VFD. It seems like it might work, but............... To make it more interesting, the grinder has 3 motors: The hydraulic pump, the spindle, and the coolant pump so the motors would be switched in as needed. Sounds like a good way to fry a VFD, but I'm not sure.

Just thinking here (normally a dangerous condition :grin:), I may not actually try it.

Opinions?
.
.
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Hi Jim,
I have not used a RPC to make 480v through transformers, but the idea would work- at least in theory.
maybe another way of doing it would be a wye start/ delta run,.
start the motor on low voltage to spin up, HI Voltage delta for the run
 
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Ulma Doctor said:
Hi Jim,
I have not used a RPC to make 480v through transformers, but the idea would work- at least in theory.
maybe another way of doing it would be a wye start/ delta run,.
start the motor on low voltage to spin up, then switch to Hi Voltage delta for the run
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That's a good idea Mike, I've done that with big motors in heavy industrial applications (100 HP +), hadn't thought about doing that with a smaller motor.
 
hey Jim i saw a video a while back that may help out


i think i got my delta wye reversed in my sentiments in my above post
 
For what it's worth, I have 30A 240V service, and an autotransformer to bring it up to 480V. A 2HP 460V idler motor will start without a pony motor with a phase-shifting capacitor to its third leg. By itself, that would draw more than 30A so I have a series resistor to limit the current which is switched out automatically by a potential relay at the load end of the resistor.

There's no sequence of pushing buttons to remember; I flip the switch and the idler starts. I run a 550V mill from it. It took some experimenting with capacitor sizes (which can get tricky, not to mention dangerous, at 480V) to get things balanced. But it has worked fine for years, and allows me to use my mill in a house with a 60A entrance.
 
JimDawson said:
I have 3 phase at the street, but I just don't want to pay to have it brought in. And then there is the permitting issues, would probably cost more than the service. I really don't want any inspectors around here for a number of other factors. My limitation is the wiring to the shop, I could pull in a 100 amp, single phase wiring. I have enough power at the distribution panel.
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Is there some common Farm related reason for 3 phase that wouldn't raise any eyebrows? Then after they leave tap the supply for the shop. Or just pull out your roll of Ben Franklins and pretend to count it when the inspector shows up. :cautious:
 
coolidge said:
Is there some common Farm related reason for 3 phase that wouldn't raise any eyebrows? Then after they leave tap the supply for the shop. Or just pull out your roll of Ben Franklins and pretend to count it when the inspector shows up. :cautious:
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I guess I could bring in a 100 amps to run my ''irrigation pump''. A lot of those out in this area, in fact, that's the main reason there is 3 phase everywhere out here. A saw mill is a permitted use too.........Hmmmmm ;)
 
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