single to three phase , beat this with a rotary ?

For all of those who are thinking of saving money via cobbling up some sort of rotary converter. Try beating the price, size, efficiency,forward/reverse and variable rpm capability of VFD systems such as this.

ebay

251003977152

I like the VFD for many reasons. But the VFD is for only one motor at a time and probably needs some programming tweaking if used with a different motor. The book with mine is 183 pages!

Well buickanddeere I just built the fifth one I ever have done this last week. I have used the original for over thirty years running a lathe and milling machine. Each of my sons and my brother now have ones we built.

I use a used three phase motor and old single phase motor we had left off of a silo unloader. I buy the couplers off of Grainger. I put a six inch pulley between the two shaft couplers. I them weld the whole assembly together. I then just bolt the motors on a board with the home made coupler/pulley hooking the motors together. Wire it up using simple blade type switch box.

To use them you just spin the pulley with the bottom of your shoe and turn the switch on. You are good to go.

Total cost was less than $75. The others cost me even less than that. So I am guessing that the $275 dollars saved would buy all of the lost electric I am losing over the inverter type for the next fifty years or so.

I know you purest out there just go crazy when we talk about a rotary converter but they work and are cheap. You have to remember that most of us don't need three phase for very long. Mine might set for weeks at a time and never be used. So when is the energy cost ever going to be an amount to worry about??

I have a question for you Mr. B and D.
If you ran a 3phase motor on a single phase line would you blow it up?
IE: A 220VAC motor that needs 3 phase to run and you ran it at home off the standard 100 amp breaker box, with 2 110VAC lines to make the 220vac (cause you didnt have a phase converter)

If you try to run a 3 phase motor on single phase it doesn't hardly run, amps up then licks out the overcurrent device. If you don't have an overcurrent it tries to run until it burns out. Same thing that happens if you have 3 phase motor and one leg drops out.

I used to help my dad build converters in the 70's. You can use two banks of capacitors or capacitors and an old 3 phase motor for a rotor. You will have to tune the circuit using capacitors to match the motor with the load to use minimun current.

A single to 3 phase converter is lucky to be 75% efficient. You are lucky to get 25 hp out of a 30 hp motor.

Blow it up?? Depends.....If the motor is equipped with proper thermal overload protection which protects the windings it will trip out before it gets too hot so NO it wont blow up. Its just NOT a good engineering practice without a rotary converter or a VFD, it can be made to start (remember a 3 phase self starts unlike a single phase that needs to be cheated n coaxed and at what direction) and run but at a much reduced HP and its not gonna be well balanced, even if youre using 220 volts out of a standard home panel thats STILL only single phase.

John T Too long retired electrical engineer and rusty on this stuff so no warranty

One thing not often mentioned about VFDs is the power savings. Most mushroom growing operations around here are using them on their A/C units and other large motors in their operations.I have both ways in my shop and like the VFDs for their variable speed and soft start/stop capabilities. The guy at the motor rebuild place in town said that a VFD on a big A/C unit will pay for itself in about 6 months with electricity savings!

Hey, JD I always wanted to build one like that. I'm not understanding why you need to push start it. I thought that was what the single phase motor was for, to start it. Can you run a air compressor with this setup?

Rare is the person that has all the parts laying around for free to build five converters.

Don't know where you have been during the conversation. You still want to cobble together a rotary converter? Have you ever put an oscilloscope on the output of a rotary converter and seen the distorted voltage and current? Even wonder why three phase motors supplied from rotary converters can not reach full rated capacity. Even at part load they are noisy and overheat. Does a rotary provide soft start, reversing, variable speed or locked rotor protection? How much are you paying for power btw ?

I use a home made rotary phase converter. Powers
my lathe, 2 Bridgeports, Karcher pressure washer,
and 10 hp compressor. Electrical bill is reasonable. Checked with oscilloscope and patterns were not to bad(can use cnc mill with no problem). It is self exciting so it starts with the push of a button.
The only thing I am going to do sometime is build a box and put the 10 hp motor outside bedause it is quite noisy. Total cost was $275.

It's noisy because the windings are placed 120 degrees apart but power is entering 180 degrees apart. Then the third leg is 90 out of phase with the input power and 30 degrees. No wonder the rotary converter is noisy with the harmonics and unbalanced currents.

No limit on the size of VFD's. ebay, kijiji and
craigslist have lots.
Yes a rotary system will provide protection same
as a three phase utility connection. Through the
motors short circuit and thermal devices.

Any old three phase vfd an be supplied with single phase and
output three phase at 57.7% of the vfd's nameplate capacity.

Any old three phase vfd an be supplied with single phase and
output three phase at 57.7% of the vfd's nameplate capacity.

Interesting timing for this topic. I just bought a vertical mill this week and of course it is 3 phase. Spindle is only 2 hp but with the table servo and DRO I went for a 3hp VFD since this is my only 3 phase piece of equipment in the shop.

Luckily my home pulls off of a 3 phase main line but right now it is cost prohibitive to drop 3 phase service to the shop. Maybe if I had more need but I don't plan to be here forever...

Yes. No. No. Maybe. Nothing.