Rotary

I'd like to build one with a 7.5hp output. I'm assuming a 15hp 3 phase motor but am confused on what capacitors I will need along with the other stuff.
 
Hi Phil , Sounds like your thinking of building your own. I would assume that your powering up a 3hp machine if you have chosen a 7.5 hp motor for your RPC. The RPC motor should be atleast 2X the size of the motor its driving min. If you want to keep things simple, I would just pony start the converter. Ilike the pony start because it takes a ton of wiring out of the mix. I also havnt had much luck with the offshore caps being reliable as well. Could be just the source I was purchasing form, not sure. For a pony start, you only need a small 1/4 to 1/2 hp 120 volt motor for the job. You could even wrap a rope around the shaft and pull start it like a old lawn mower. No need to get fancy here. Some guys want the push button start, its a personal choice really.
 
Ok, see your going to power 3-machines. Providing its only one at a time, just use the X2 to base it off. The choice of motor can make a huge difference with noise output. The least amount of noise would be the 1200 rpm motor. The usual is the 1750 rpm motor. The 3600 rpm motor I would not use, those guys are turning a lot of rpm, and with rpm, the noise level goes up with it. For the simple RPC, and pony start, I just round up the following parts. The main motor for the RPC, chosen buy the HP I intend to drive. Also, the lowest RPM as mentioned above. A pony motor of 1/4 hp on up to get the big guy spinning. The main motor and pony will need sheeves, and try to size the them to get you main motor spinning at name plate rpm, they start easyer. So, 2 pulleys, 1- belt, then I allways favor the cuttler hammer 3 phase disconnect box. That is your main basics for parts, other than wire. Most all of this you can dig up in craigslist and such. If you seach for my posts on RPCs , you should find pics of my simple RPCs I posted some time back. I also do not bother with run caps, or any balancing. Machines like lathes/mill are used under variable loads, and different loads will drive you crazy trying to balance them.
 
Thanks. Let me do some research and call around to find a motor and ill post back wit the progress.
 
Found a local shop that I can get a used 15hp 3 phase motor from for a couple hundred bucks with a warrenty he said. I've had no luck with any local scrap yards or Craigslist. Here is what I think I will need. Correct me if I'm wrong

Main motor. 15hp 3 phase
pony motor 1/2g hp?
square d 3 phase disconnect box
3 phase wire to hook up each machine. Can 3 machines be hooked up to the square d box or will I need a seperated box with multiple outlets that I can put a plug on each machine and plug into this box? Also what size wire should I buy?
 
Phils69 said:
Found a local shop that I can get a used 15hp 3 phase motor from for a couple hundred bucks with a warrenty he said. I've had no luck with any local scrap yards or Craigslist. Here is what I think I will need. Correct me if I'm wrong

Main motor. 15hp 3 phase
pony motor 1/2g hp?
square d 3 phase disconnect box
3 phase wire to hook up each machine. Can 3 machines be hooked up to the square d box or will I need a seperated box with multiple outlets that I can put a plug on each machine and plug into this box? Also what size wire should I buy?
Click to expand...


I'm a little late to the party here, but I wanted to add a few things.

Even if Phil didn't have other machines to run, a VFD would not make sense here. This machine already has a variable speed drive. It uses a motor/generator (MG) to provide DC to the spindle motor, so the variable part of the VFD provides no benefit. The MG wants 220 3-phase, not the 180 VAC that most VFDs put out. A VFD that can provide 220 3-phase at the current level that this machine requires is pretty expensive. I don't know of anyone running a 10EE MG machine from a VFD. Some folks, mostly guys that didn't understand or appreciate what they had, have torn out the MG and DC spindle motor and cobbled in an AC motor and VFD, but it does not deliver the performance of the original drive.

Phil,

I use a 7.5HP idler motor with my MG 10EE and it works just fine. I would not go the pony motor route. All you need to start the idler motor is a simple potential relay and a pair of capacitors. If you're comfortable doing house and shop wiring, it will be easy enough for you to build. A pair of run capacitors are a good idea to add to the converter to balance the current on the artificial third phase.

You should be able to pick up a used 7.5HP 3-phase motor to use as the idler motor for under $100. The rest of the parts for the converter are probably under $50 and you can build it in an afternoon.

My converter is on a 30A circuit. I'm sure it's not to code, but I have all of my 4 machines hard wired to the converter. I use ¾” EMT and 4x4 boxes to get power to the wall behind the machine, then flex conduit to the machine. You can use outlets and cords if you like. Add as many outlets as you like.

(Assuming a 7.5HP idler motor) use at least #10 wire; #8 for long runs. Locate the converter near the circuit panel if possible. All the wiring to the machines, including the cords should be at least #10. Each machine should have fuses size to the particular machine's wiring. Note: the circuit breaker and the fuses are there to protect the wiring, not the machine; overload devices on the machine are used to protect its motor(s) from overload.

Do yourself a favor and run 5 wires to each plug (or box if you're hard wiring): 3 black (or red, black, blue), green/bare safety ground and white common wire. Adding the white wire allows you to put a 120 work light at the machine, if desired. (Also, if your 10EE’s exciter fails, having 120 at the machine will be very helpful for reasons I won’t discuss here). I prefer metal conduit (EMT) and stranded wire. Don't put Romex cable in a conduit, get individual wires and pull them as a bundle.

If you have a recycling place near you, see if you can buy the wire from them instead of paying full fare; these guys are going to sell their wire to China by the pound (and they get less per pound because it's insulated), so will often sell to you for a small mark up over what they get for it. Just make sure you know what new wire costs per foot before you go in. You pay through the nose for wire at Home Depot or Lowes. Electrical supply companies are cheaper. If you have a contractor buddy, see if he will buy wire for you on his discount.

Most of the noise from an RPC is the idler motor's fan, which is usually pretty primitive. Since the idler motor isn't running at its name plate power, it doesn't need as much cooling. I took the fan off my idler motor and it's very quiet. I keep track of its temperature and if I'm going to be running it for a long time I put a floor fan on it so that the case never gets too warm to touch. A lot of motors are spec'd for a 50 degree C rise (90 F), so they can run a lot hotter than mine ever gets.

I wouldn't be particular about the brand of 3-phase disconnect. Get one that's rated for at least the HP size of your idler motor.

Cal
 
Do you have enough power to run that 15hp motor? I don't thing a 50a breaker/wire will do it. Going larger starts to get expensive fast.
 
Good point Dave. I'm in a garage with normal service. Would that do for a 7 1/2 hp idler motor?
 
Phils69 said:
Good point Dave. I'm in a garage with normal service. Would that do for a 7 1/2 hp idler motor?
Click to expand...

Normal as in 120V/15A/1P ? If you plan to set up shop probably wise to run a 50-100A sub panel up to the garage and go from there.
 
You must log in or register to reply here.
Back
Top