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3 phase homemade converter from a 7.5 motor need plans and help.

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Forum topic by liketosail posted 03-06-2013 04:15 AM 2749 views 0 times favorited 7 replies Add to Favorites Watch
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liketosail

31 posts in 1404 days


03-06-2013 04:15 AM

I plan to build a 3 phase rotary converter from a 7.5 hp three phase motor and need some good plans.
Does anyone have any?
Also my largest motor is five hp I will be running.


7 replies so far

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Loren

8302 posts in 3111 days


#1 posted 03-06-2013 05:12 AM

I bought a panel from a fellow on ebay who calls
his units “Phase-Craft”. It was about $130 for
a box for a 5hp idler motor. He makes them
for larger hp idlers too.

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liketosail

31 posts in 1404 days


#2 posted 03-06-2013 05:29 AM

Thanks I will look at that, the price is low.
but if it works that is what matters.

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TopamaxSurvivor

17669 posts in 3139 days


#3 posted 03-06-2013 05:36 AM

http://wiringdiagramcircuit.com/3-phase-to-single-phase-rotary-converter/ That should do it.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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REO

889 posts in 1537 days


#4 posted 03-06-2013 04:02 PM

If your building for a specific motor capacitance can be very specific and the load is pertinent. If you are planning to use it for several motors it is much less specific. I took a look at TOPA’s link the suggest running a larger idler. I have found that running a smaller motor is more efficient. I have read that it is possible to run three times the horse of the idler. In my own experience I have run a 3 hp with a single horse for several days of production on a turret lathe. I ran a 2 hp mill on a one horse converter since1979. Still running strong. try to gt an older motor for your idler. It will typically have better insulation and take the current surges as you start the other motor. The run capacitors just balance the voltage across the legs. The mill has run without balancing caps the whole time. I have a 7.5 that I run for a cnc router and I have not bothered to balance that converter either. The first 1 hp I built I just hand spun a 5” pulley to get it up to speed. The second 5 hp I used a lawn mower starting rope. The last few I have cap starts. I have some graphs for balancing guidelines somewhere I try to dig them up. If others are interested I can post them here.

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Loren

8302 posts in 3111 days


#5 posted 03-06-2013 04:07 PM

Also, you’ll need to run a 220v line with about 40
amps on each leg in order to run that idler.

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REO

889 posts in 1537 days


#6 posted 03-06-2013 04:34 PM

The name plate amps are at load. The idler sees no load. It draws only enough current to keep spinning. You do have to keep in mind that if you plan to run a motor with a loaded rating of 10 amps/240 per leg 3 phase you will have to feed it with somewhat north of 15 amps/220 per leg of your single phase supply. with a capacitor start the load isn’t to bad. most breakers are designed for a short term overload for motor starting(less then a second) I know fellow who runs a 60 horse RPC so he can do injection molding on his farm. It seems like it takes all day for that thing to wind up. actually it takes about 4.5 seconds. another thing to consider is that you should use a magnetic starter for your load motor at least or for your RPC in case the power fails, for safety.

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TopamaxSurvivor

17669 posts in 3139 days


#7 posted 03-06-2013 06:27 PM

I have never done this. I have wired commercially available roto-phases. I only know of one guy who wanted to run a compressor for his 8 bay auto shop. Since cheapest is always best, he got some one to put in the smallest single phase panels he could. His compressor was too big for a single phase motor. My price was too high to put in a rotor phase. He got some one to put in an idler motor. He called and wanted to know why he had to spin it by hand to get it started? ;-)) A year or 2 later he wanted to know why his compressor motor burned up? ;-)) They finally just put in a 3 phase service. It was available. Cheapest wasn’t best after all ;-))

It sounds like REO has experience doing this successfully. Lathes and mills are less demanding than a compressor.

The guy using it for 60 hp must be affecting the earth’s orbit when his kicks it on! ;-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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