Rotary Phase Converter-Idler Moter RPM?

A "balanced" 3 phase motor has all 3 phases pulling nearly the same amps. The standard quick and dirty field test is to use an Amprobe successively on each of the 3 motor leads to check the current load per lead. A balanced motor runs smoothly and delivers full rated HP without cooling issues. An unbalance motor heats the heavily loaded windings more than the other(s), and in extreme cases cannot deliver rated HP.

Out in industry, large plants with 3 phase power systems can experience imbalance if there are a lot of connected single phase loads such as resistive heaters or lighting. If a plant system becomes too unbalanced, the motors experience "unbalanced" amp loads. The designers and electricians always try to arrange and connect the single phase loads such that the system, as a whole, remains mostly balanced.

For RPC users, with only 1 or a few motors on an RPC, the unbalance is due the capacitors (or lack of) in the system. Many users run RPCs successfully with little or no balancing. From what I have seen, you only need to have a well balanced system if one or more of the motors routinely run near rated HP, or if you have 3 phase electronics such as CNC drives and the like. With an RPC system, you can use a voltmeter to estimate the balance by comparing the voltage between each of the 3 phases.

Terry S.

edited to correct spelling
 
When I started out with a home shop I acquired industrial equipment from a high school shop.
They had 1/2 to 1 HP three phase motors.

The factory where I worked was required to convert motors to TEFC by an Insurance Co.
The motors removed were in a pile in the corner of a storage room. I received permission to obtain a 5 HP
motor to build a RPC. It was a huge heavy motor twice as large as a modern 5 HP with a 1.25 dia. shaft weighing over 100 lbs.

A welded frame was made and the 5 HP was bolted down. A 1/3 was bolted next to it and they were belted together.

A stand off was added and an electrical enclosure was bolted on. Incoming 220 v single phase was fused and a
2 pole switch added for On/Off. 120 volts were tapped off and fused and a toggle switch added for the 1/3 hp motor.
for the output power a 3 fuse block was installed. I know lots of fuses but my Dad didn't want me to burn down his building.

To start the converter, switch on the 1/3 to get things turning . When up to speed engage 220 v and turn off the 1/3 hp motor.


Later some running capacitors were added to help bring up the voltage of the induced leg.

I have since sold the 3 phase machines but my brother still regularly uses the converter with his home shop equipment.
Its still running 40 years later.
 
INNERESTIN' About to start a RPC build, in Au one is limited to how many amps one can legally draw off of the single ph. supply, 40 amps max
I have a hyd power pack 3 hp, which will not produce enough grunt to split wood, thru a vdd rated at 10hp, I had to run it back on 3ph. from my Lincoln welder/genset and with fuel 10 dollars gallon here makes it expensive
I have a 12 hp lathe and a bandasw, the latter on vhd but not a lot of boogie, so IMO VHD are a bloody lie
I will endeavor 15 to 20 hp RPC
saw this on youtube
any other advice would be welcomed here
 
Stuart, on 40 amps per WIRE you can easily drive a 20 hp rotary converter that should handle the inrush from any 12 hp motor out there. 40a is the upper limit for US 10 gauge wire, so for household installations the Aus code makes sense. It's not even that restrictive, tbh. I have the option to run big wire to big motors as long as my panel and service matches, but most of us are working with residential power as well.

Oh, I see... I just tripped for a sec working the numbers, but it comes out the same. On 230v EU/Oceania power, you are on a delta tapped system. In the US, we are on a wye-tapped system, so we can draw 40 amps off each split phase, but that's 110v from each line to neutral, so 2(40a*110v)=80a*230v, so it's the same in the end, but your breaker will need to be 80A (line to neutral). My breaker is 2x40a line to neutral. Both are 230v. The difference is you have thinner wire for the 230v mains than I do for 110v, so my ampacity is higher. Hmm. Are your breakers single pole, or two pole? If you're single pole, you might not get the capacity you want without running heavier wire. You're going to need to check with an Australian electrician, probably. Do your RPC generator motors have to run backwards because of the inverse Coriolis effect? I'd better figure that out, too, there are more layers to your question that I initially thought.

My houses in Germany all had 230 3-phase service, and the house I just sold there had 440v/230v 3-phase in the shop/garage... I guess the Americans would have to charge extra for that.
 
pontiac428 said:
Stuart, on 40 amps per WIRE you can easily drive a 20 hp rotary converter that should handle the inrush from any 12 hp motor out there. 40a is the upper limit for US 10 gauge wire, so for household installations the Aus code makes sense. It's not even that restrictive, tbh. I have the option to run big wire to big motors as long as my panel and service matches, but most of us are working with residential power as well.

Oh, I see... I just tripped for a sec working the numbers, but it comes out the same. On 230v EU/Oceania power, you are on a delta tapped system. In the US, we are on a wye-tapped system, so we can draw 40 amps off each split phase, but that's 110v from each line to neutral, so 2(40a*110v)=80a*230v, so it's the same in the end, but your breaker will need to be 80A (line to neutral). My breaker is 2x40a line to neutral. Both are 230v. The difference is you have thinner wire for the 230v mains than I do for 110v, so my ampacity is higher. Hmm. Are your breakers single pole, or two pole? If you're single pole, you might not get the capacity you want without running heavier wire. You're going to need to check with an Australian electrician, probably. Do your RPC generator motors have to run backwards because of the inverse Coriolis effect? I'd better figure that out, too, there are more layers to your question that I initially thought.

My houses in Germany all had 230 3-phase service, and the house I just sold there had 440v/230v 3-phase in the shop/garage... I guess the Americans would have to charge extra for that.
Click to expand...
thanks so much, will answer later today
 
You must log in or register to reply here.
Back
Top