Upgrading my simple RPC, questions

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I am very close to moving into my new shop space. When I do, I would like to upgrade my RPC for the lathe. First let me say that I don't find VFD's to be an option, call it bias, lack of experience, bad decisions or hard-headedness. I like the RPC and the ability to use the machine as built. For the record I am powering a single lathe, a Logan 12" with 2 speed motor and a really handy Reeves Drive, all this in a machine from the 1960's.

What I have now is a simple unbalanced RPC as detailed here MY RPC . I am using a 7.5hp 3ph motor as an idler, I have no caps to balance anything out. To start the RPC I wrap a small rope around the idler shaft and give it a pull to get it moving, then hit the switch and we're off.

Now, what I would like to have when I move is an upgraded control panel. I would like to have a way to simply push a button and the panel start to motor and keep it going without me having to spin the motor manually. My question is how hard would that be to build myself, and would it just be worth it to buy a panel to hook up to my idler motor? If buying a panel, what brand(s) should I look for and which ones should I stay away from? At one point I thought one of our members made panels for sale, is the correct? If so who?
 
There are RPC kits without motor on ebay that's a good deal. Or build it all yourself. here's one fine tutorial.

<EDIT> here's the eBay offer for a 3hp. I think this vendor would have a 7.5 also.
www.ebay.com

3 Hp phase converters control panel CONVERTER ROTARY made in USA RP03 | eBay

With this setup you will have a 3 hp rotary phase converter, your 3 hp motor should be rated at 230volt or 230/460volt and a rpm of 17XX or 34XX. Rotary Phase Converters. Rotary Phase Converter Panels.
www.ebay.com
 

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I think all you need is a motor starting type capacitor and a push button to start the motor instead of pull-starting it. You would connect the cap in between one of the incoming power legs and the 3rd generated leg of the RPC. The button would be in series with one of the cap legs to connect it momentarily when you push it.
Not sure what value cap you need- Mike probably can give you a ball-park figure- I'm thinking about 200 microfarad at about 400 volts, oil-filled type
-Mark
 
I ran into the same problem as you have, a two speed motor. I couldn't figure out away to run it off a VFD. So I put in a rotary phase converter. It works so I am happy. I didn't have to rewire the lathe ether. Have used a VFD on my surface grinder and mill that worked out fine,but a two speed motor i had no clue.
 
Adding a starting capacitor to one of the other legs of the three phase motor to spool the motor up
is quite easy to do. I turn on the main power and push the momentary switch simultaneously and
hold it down until the motor is up to speed. My motor has large cast iron pulley sheaves on it which
makes it very smooth running. You need a hefty momentary switch or alternatively use a heavy duty
relay to power the capacitor. Evening out the voltages can be accomplished by adding capacitors across
the legs but not necessary in my experience.
 
7.5 hp will need around a 500Uf capacitor to start quickly.
A 400Uf cap would be the very least I would attempt.
The panel is simple to build.
I would be happy to help out or wire it up or to make a panel for you.
 
Ulma Doctor said:
7.5 hp will need around a 500Uf capacitor to start quickly.
A 400Uf cap would be the very least I would attempt.
The panel is simple to build.
I would be happy to help out or wire it up or to make a panel for you.
Click to expand...

I would enjoy building it myself, I don't have a problem with things like that. What I do need is schematic and parts list. I did find this 'kit' on the 'bay and wonder if it is what I need and/or priced well https://www.ebay.com/itm/7-5HP-Rota...134475?hash=item264360300b:g:rzQAAOSwo4pYNIuX
 
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I made my own RPC using a static phase converter for starting (I already had it) and used oil filled capacitors to balance the voltages; it works fairly well, but some machines spool up more slowly than they normally would on "real" 3 phase. The RPC motor is 1750 RPM, and my lathe has a two speed motor, 1750 and 3450 RPM, it starts well on low speed, but is slow to spool up on high speed, which I rarely use.
 
It may be worthwhile to purchase a 7.5Hp RPC control panel unless you happen to have parts readily available. Getting the right specs. and decent components, I often find I am not saving that much at the end of the day. They also have some safety detection circuits for phase loss.
www.ebay.com

CP-7 Pro-Line 7.5HP Rotary Phase Converter Control Panel - Loaded with Features | eBay

Add your own motor and make a rotary phase converter. Rotary Phase Converters. 7.5HP Pro-Line Rotary Phase Converter CP-7. Static Phase Converters. Digital Phase Converters. Easy / Light Motor Loads - up to 5HP.
www.ebay.com
 
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