Need Help On Converter Choice.

Zachp

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Ok I bought a leblond 15c lathe a few weeks ago. It has a 7.5 hp motor on it. My question is what is the best way to get 3 phase to this machine? I have 100 amp service in the garage. Static converter? RPC? Change the motor out for a smaller one? I have found a 25 hp RPC for a good price but I'm afraid that it will be too much to start on my 100 amp service. What kind of startup amperage will this draw? I may purchase a compressor, or a bandsaw somewhere down the road so that has me leaning toward a RPC. Suggestions?
 
Investigate the term VSR, it seems to be the latest improvement in converting single phase to three phase. I'm a tool maker, not an electrician, and this is new since I retired 15 years ago.
 
The vfd for this size motor is out of my price range. I put a vfd on my Bridgeport since it is only a 1 hp motor. The affordable vfd's only go to 3 hp I believe. Thank you for the suggestion though.
 
Your lathe has a 7.5 HP motor, so your minimum Idler (RPC) motor size will need to be 7.5 hp. No need to run a giant RPC, the cost of operation is fairly low for what it provides.
Static phase converters are not (at least back then) that great as they convert three phase motors to single phase resulting in loss of power and run hot.

VFD's provide the ultimate control and options but as you know come with a price for larger units.

I have been using RPC (balanced) for 15 years now. The current set up is wired in conduit thoughout the shop and provides power to nine machines. I'm a one man shop, so running more than one machine at a time is not common, however I have run (no load) two mills, lathe, cold saw, band saw, iron worker at the same time with excellent balanced (+/- 3 volts) readings. In essence, each machine becomes a RPC for the next (I believe).

Check out Phase Craft on ebay, I purchased his control panel for a 7.5 HP Idler for $200 free shipping. It came prewired and balanced. The motor I used is the same motor from my old shop's RPC and runs quiet and efficient. You send him the information on your idler (size,RPM,service factor.etc) and he builds the panel accordingly and balances the legs.

As you can see from the photos, the machines are decent size and run fine on a 7.5 HP RPC. The largest machine (iron worker) is a 5 HP unit. The RPC is on a 40 amp circuit on a 200 amp sub panel.

I recently added a VFD (with the help from a fellow member MJ) to the plate roller for more control. The VFD allows for POT, hour meter, ramp up/down, braking, as well as torque values to be adjusted. This VFD does not convert the power to 3 phase in this case as I use the RPC for that.

I hope this helps.20140901_143041.jpgIMG_0072_2.jpg20140913_185120.jpg20140901_092804.jpg
 
Thank you both for your replies.

I had a friend that has a home machine shop tell me to double the idler motor size to the size of the load. Is this not true? If i have a 7.5 hp motor on the lathe, then a 7.5 RPC will be big enough? If that is the case I should be fine. I may opt for a 10 hp unit to allow a larger compressor down the road. Can anyone confirm this statement for me? I hate to keep asking stupid questions but this is all new to me and im trying to get everything set up as soon as i can so I can start using the equipment. I have some small parts that a friend is wanting me to make and I am sure it is going to take some practice to figure it out.

Just to clarify:
The Leblond lathe has a 7.5 hp motor
The bridgeport has a 1 hp motor with a VFD on it
Need to know the minimum size of RPC I need to run the lathe.
 
It's been a very long time since the research was done on the original RPC, but I tend to remember key items. If memory serves, your idler must be the same or larger, but never smaller. It was never an issue for me as the biggest load comes from the iron worker at 5 vs. 7.5 RPC.
If you have the option to go 10 HP, then thats a better match imo. I'm sure someone else will chime in to add more information.
 
Ideally you want a idler motor twice the size of largest motor that will be used. Talk to the guy at Phase Craft, he builds good stuff, and responds to questions. He is on ebay and has lots of models.

michael
 
I guess I should add to my question a bit. While picking up some parts for the lathe and mill yesterday, the sales guy looked in his manual and the machine originally had a 3 hp motor on it. Someone has put a 7.5 hp motor on it somewhere in the past. Would this have any affect on the RPC sizing? Or do I need the double size still?
 
IMO, if you were to get a 10hp RPC you could easily run the lathe and the BP at the same time as long as the lathe was started first, then the BP.
care should be taken to make the single phase load lines to be heavy and have the proper size breaker.
i have started 10 hp motors with a 7.5 hp rpc, i'm not recommending the practice , rather giving a point of information.

your 7.5 lathe motor won't be working hard to power the lathe.

have you considered downsizing the motor???- you can get away a lot cheaper in wiring and other ancillary supplies necessary to install and run
 
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