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04-19-2017, 12:19 PM #1
What do I need to power a few three phase machines? RPC Questions
I've been reading a great deal about rotary phase converters and I had some questions I hope you all can answer. Currently I have a 3 hp 3 ph. chicago press brake. I also have a 1 or 2 hp bridgeport that is also three phase. I was planning on buying a RPC from American rotary. When I called them, they said because my brake is 3 hp, I will need a 7.5 hp RPC. It is around $640. I started reading on here and now I may try to build my own to save some $$$. I went to the local scrapyard and the only motors that I could get to are a single phase 5-7 hp motor and one 5 hp 3 ph. motor. I would like to build a setup where you use the single phase motor as the pony and the 3 ph motor as the idler motor. The only concern is that the idler motor is only 5 hp. Do you guys know if this motor is enough to power my 3 hp brake? There were plenty of 10 hp single phase motors there but that didn't help me. I was hoping they were 3 ph but no such luck. I suppose I could use the 5-7 hp single phase motor on my brake but then I can't use anything to power my bridgeport. Looking at the pony/idler setup looks somewhat easy to setup. Ive seen some that have one motor and all sorts of wiring/capacitors, etc... and that seems too complicated for me at this point. What options do I have here? Thanks guys.
04-19-2017, 02:50 PM #2
A 5hp 3 phase motor does not need a single phase motor to start it. I use the equivalent of 210uF to start my 5Hp RPC. A relay with a start button is all it takes.
Those RPC companies use cheap parts from china and give you the idea that you are getting a gift from the gods in exchange for very little money. You can build a better RPC if you do it yourself.
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04-19-2017, 02:54 PM #3
Yes, the five horse is suitable to your needs.
04-19-2017, 03:27 PM #4
You lost me a little bit. You both are saying the 5hp 3ph motor I have WILL work for my lower hp machines? The 210uF is a capacitor, from what I saw. I can use that with a relay and start button to start the 3ph motor with single phase? Does anybody have a link to where I can find how to wire this? Like I said, from what I have seen from this site so far, people either have the pony/idler setup or a setup where it looks like a damn bomb with wiring all over the place and capacitors/transformers galore and it makes my head spin. Thanks guys.
04-19-2017, 04:51 PM #5
The "bomb wiring" is the automatic version of what Ron suggested. He suggests essentially using a push button to connect the cap during start, and as soon as it does start, you leggo the button and get to working.
Because of the high current, he is (and I agree) suggesting that a contactor be used to make the actual connection of the capacitor, with the push button simply used for connecting coil power to close the contactor.
Generally, the 5HP should work with a 3 HP motor. Press brakes are a little hungrier as to power as they bottom out. We had another guy ask here who had trouble with his, although admittedly he was way down a weak power line out in the sticks. He had to reduce hydraulic pump gal/min to get his to work acceptably.
So I am not as ready to jump up and agree on the 5 HP. The suggestion of the 7.5 HP has some decent reasoning behind it. The 5 HP should run any other stuff around the shop if nothing is larger than 3 HP.
Can you show the data plate of the 5 HP in a clear pic? It may have some useful info for your situation. Some motor types are more suited to RPC than others. A pic of the motor data plate on the press would not hurt either.
04-19-2017, 08:41 PM #6
Can you find TWO 5hp 3-phase motors?
if so, start the first one, then throw a switch to bring in the second. ;-)
You can make a rotary converter with nothing more than one three phase motor, a hand-operated switch, and a 10" boot-string.
Connect your AC mains to switch, and from switch to any two of the motor's three legs. Wrap bootlace around the motor shaft, give it a good hard pull, then throw the switch. Three phase motor will run up to speed, and at that point, you'll have three-phase power from the two (driven by single) and the third (unconnected) leg.
Anything more complicated than that, is just luxury, safety, and equipment protection.
And I agree with Ron... you can most often build them better than you can buy 'em, using left over old motors.
The scrapyard you have, that's only got big single phase motors, is probably getting mostly agricultural scrap. The larger single phase motors are used in grain dryers. Single phase motors in the 5-20hp range are quite frequent for scrapyards that deal with lots of factory closures, building remodeling, and similar situations.
04-19-2017, 09:08 PM #7
This is a simple one.
I suggest that you start with:
- the 5hp motor.
- wire: black, white, red, and green.
- piece of rope.
Do what Dave suggests, and get that working.
Then you can add a start and stop button with a few capacitors. I use 50uF between L1 & L3. 90uF (50 + 40 in parallel) between L2 & L3. I have 120uF (50 + 50 + 20 in parallel) that I connect between L2 & L3 for starting. The 90uF already there gives me a total of 90 + 120 = 210uF. When the start is over the 120 is switched out. All caps are oil filled. (Ashamed to say that I bought them at Grainger).
Here is a something for you after the rope pull is working:
M1 is just a 24 VDC coil. You can get a contact block with 24VAC, 120Vac, or 240VAC. Doesn't matter too much. I like the 24VAC coil way (which uses a 220:24 transformer) and a couple of 24VAC lamps.
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04-20-2017, 05:37 AM #8
Thank you guys for breaking it down for me. I am finally starting to understand it. I understand the top diagram you gave me also. The question I have now is about portability. I would like to use this on a couple of machines right now and more as I add to my shop. This diagram looks like I need to wire the tool motor to the phase converter. Ive seen videos on YouTube where there is the pony/idler setup and a three phase plug on the converter. This would be ideal as I can go from machine to machine. I hope this makes sense. Thank you guys.
04-20-2017, 10:36 AM #9
Here is a inexpensive adjustable relay that you can use to control the closure of the RPC start contactor/relay for switching your start capacitor(s). For a 5hp motor with 220v single phase source, all you need is a fraction of a second, no more than 1 second. Usually these things have a span of 1 to 5 or 10 seconds. Some go out to minutes.
Macromatic Time Dlay Rlay, 12VAC/DC, 1A, DPDT, 3 sec. TR-51622-12 | Zoro.com
Notice the screws pointing up into the white housing from the black base. You can open the compartment and change the time constant of the circuit very easily.
Some people like the potential relay method, but not me. Do I have to explain why?.
Here is a simple diagram for a start/stop switch. The M within the circle means the contactor coil. The M with parallel bars means a normally open auxiliary contact on the main contact relay. The link has a lot of other diagrams too.
rpc start circuit diagram - Google Search
04-20-2017, 01:16 PM #10
Thanks again for the help. Rons and DaveKamp, would you guys be able to talk on phone? I have a few questions and you fellas seem pretty knowledgeable. Thanks guys!
04-20-2017, 06:13 PM #11
Two 5 HP three phase motors has merit. You could probaboy use a 5 HP and a 2.5 HP, or 3 HP for the second motor.
Run the 5 HP for all tools and add the second motor into the circuit when running you shear.
If you want to get fancy you can feed the output of your RPC into a three phase breaker panel and have a circuit breaker for each device.
In the photo below the panel on the left is 220VAC single phase, the pannel on right upper is a three phase breaker panel and in between is an single phase
AC cut of switch and the RPC.
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04-20-2017, 09:48 PM #12
04-21-2017, 05:51 AM #13
You could also go with just the 5hp converter. If the brake requires more than that, use the Bridgeport as an additional idler. Assuming that you've got them all wired together, as Vlad suggests. It's the most convenient arrangement.
I wish there were used 10hp single phase motors available around here.
04-21-2017, 10:16 AM #14
Thank you guys for the help. I am attaching the motor badge for my three phase motor below. The more I think about it, I want to build an automatic version. I am going to try to design it so it can be portable to move from machine to machine in my shop though. Rons, thank you for the diagrams you provided. The first one looks pretty simple to start. I think I will do that and once I get that working use the following diagram to add the luxury items. My questions:
1. You list several different sized capacitors. With the motor badge I provided are those still okay? I don't want to under/over power the motor with too many or not enough capacitors.
2. I would like to get contactors and relays to put with this for safety and overload protection. Is there a contactor or relay that you guys recommend I get? I'm sure there are many different kinds and I want to make sure I have the right ones for what I am doing.
3. The idler motor should be 3 phase correct? I took my motor to a motor shop the other day and he mentioned that my idler motor should be single phase but he said he didn't know anything about phase converters either. I think it has to be three phase but wanted to double check.
Thanks again for the help!
04-21-2017, 02:15 PM #15
04-21-2017, 11:16 PM #16
04-22-2017, 03:57 AM #17
Search the forum for at least some answers to your questions. About 95% of it has been covered here.
Yes, the idler motor must be 3 phase. Too bad your motor shop guy doesn't know RPCs. Sounds like an honest guy, but not very useful to you on this project.
If you can work safely around 240V, you can do it. Keep at it!
04-22-2017, 10:26 AM #18
If you looked on Craigslist you could probably find a 10 hp 3 phase idler, perfect size for a converter.