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15 HP RPC Build

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  • #16
    Originally posted by Sparky_NY View Post
    Minor point but air conditioner clutches from a car are 12V DC, not AC.
    I know, I didn't mention it as rectifiers are like $5 on ebay.

    Originally posted by deltap View Post
    Another vote for keep it simple. When the sparks and smoke start to fly you'll be happy you did. First check with your utility on what they require. Y delta and power factor correction, probably not on 15 hp. Check your electric service to make sure it can handle the added load. The motor is not starting under load and should start easily across the line on delta. Voltage balancing caps, definitely. It's a toss up on whether you use start caps and potential relay or pony motor and belt/treadle to spin it up. Use properly sized contactor, overload and wiring. A voltage monitoring control is inexpensive and can be purchased at a HVAC supply house if brownouts are common in your area.
    Disagree. I need to know this stuff. The Daewoo lathe I have is stacked full of stuff. So many contactors half are on the door. I gotta learn it someday. Why not a project with a bit more challenge than the usual.

    I won't be calling the PoCo. They would want an inspection, then the 1962 grandpa-modified wiring would have to be redone. And if I'm doing that, well I might as well petition for three phase from the street. I doubt they want me to have a machine shop at all in a residential area. Nope, nope, nope.

    I would like to put the RPC outside eventually, so slipping belts by foot is no good there. Needs to be push button.

    Originally posted by Ringo View Post
    I built my 5hp, then upped it to 7.5hp RPC. Yeah I started it with the rope pull thing for fun & giggles.
    I bought a rpc kit from Ebay put it all together, and did the balancing from the Fitch drawing. Works fine.
    Myself, I wouldn't bother with the pony motor, that start cap circuit is just too easy to do.
    All the parts can be had from your local HVAC supplier, the potential relay, the caps, all that are HVAC common stuff and not expensive.
    All the common HVAC stuff is 24v controls and run on 120v or 220v, that stuff is cheap and common.
    If you got a good electrical drawing to begin with, that start circuit is by far easier to build than twiddling around with a pony motor.
    here is a couple online suppliers,, if you need any additional parts
    ​​​​​​http://phaseconverterusa.com/15Hp-Ro...vac-_p_55.html
    ​​​​​​https://usbreaker.com/
    I used 240v control on my contactors, eliminating the need for control transformers
    Good to know.

    I'm not sure about those phase converter kits. They seem too cheap. Doesn't seem like nearly enough run caps either. How does one even balance anything with 3 caps only? No PF correction caps either.

    Originally posted by J Tiers

    Have a look at the ratings plate.

    You can use a 120V transformer at 360V perfectly well.............................................. .... as long as the line frequency is 180 Hz.

    Both transformers and motors respond to V/Hz. 120V/60Hz=2V/hz and 240V/120Hz=2V/Hz. But 240V/60 Hz = 4V/Hz.....which is a problem if the transformer is made for 2 V/Hz. Time has no particular part in the matter, it only needs a couple of cycles to show up the problem.

    Now, if the thing is actually rated for 240, or higher, at 60 Hz, then no issue. Data plate will tell.
    Lol, I wish there was a plate. Just some silkscreen paint on the top. One side says 120V, the other says 6V. 53A. Like I said, I'm pretty sure they were running 240V in. But I head ya. I've got a bunch of other unmarked transformers, I guess they are junk?

    Originally posted by Mcgyver View Post
    whats better than a one button start? A remote control start! Should be relatively cheap and easy in this day of Arduinos. I've found that I dislike the drone (and bit of power wastage) when I'm not running a machine, but it gets to be a real pita climbing across my crowded shop to turn it on whenever I want to run a machine.
    Nah. That's where I draw the line at KISS. My shop isn't that big. I can put a push button at each end if I want.

    Originally posted by Captain K View Post
    Can't help on the rest of it but every a/c clutch I've ever pulled had a tapered hub. Not an insurmountable obstacle but something to consider.
    Fair enough. Think I could bore it straight?I could build an adapter if I had to.

    Originally posted by Tundra Twin Track View Post
    I used a 15HP with 1/2 hp pony motor to start it belt slipped a bit till up to speed.There some good info on a post from a year ago Stone Hammer Simple RPC.
    Yep. I'll check it out, I remember that thread. How long did it take to spin up? Like I said earlier, I want this outside eventually, meaning no slipping of belts.

    I do not know if the 120 Volt transformer will work, without eventual failure, on 240 VAC. If it was made with conservative specs, it may very well work forever. However, a transformer with a 120 VAC primary coil, which is then operated with 240 VAC, WILL NOT produce the rated Voltage at the secondary. Transformers work with a RATIO of turns, primary to secondary. So if you double the primary Voltage, YOU WILL ALSO DOUBLE THE SECONDARY VOLTAGE. So, instead of getting the 12 VAC that you expect you will actually get more like 24 VAC. And that doubling of the secondary Voltage will also DOUBLE the current any 12 VAC component that is operated with it. Some could even burn out immediately but others will suffer from excessive heat (see note below) and may eventually fail from that. You really need to match the ratings either by using the proper transformer, or the proper input Voltage, or the other components with the proper Voltage ratings.
    Well your post is still broken, but check mine again. It is a 20:1 transformer. It is marked 120V in, 6V out. So I'm expecting 12V out when I double the voltage, not 24V. I understand where you were coming from though.

    I really don't care about the transformer. It it works, then great. If it somehow melts down in the 3 seconds I am running it (which will be very impressive, it's a good 20lbs, that's gonna take a lot current to smoke it in that time), then I'll regroup and try something else, and it will go to the scrap yard. Personally, I'll place my money on it working, since it came out of a 240V delta device. I can always yoink a xformer out of a battery charger and run it on one of the 120V legs. Of course then I need a neutral, but there is plenty of ways to skin this cat.

    Originally posted by nickel-city-fab View Post
    Even more radical idea: no clutch at all. 1hp ought to easily be able to spin over the big motor, especially with a 2:1 reduction on a belt. You could always use a relay setup (HVAC potential relay on the generated leg?) to disconnect the pony motor from the single-phase after the big one starts generating.
    Originally posted by lakeside53 View Post

    They do easily... sure there is a some start up acceleration lag, but...

    One I designed years ago runs fine. Schematic has been published on this site several times
    Ok. Worth a shot maybe. The 2HP motor in the minimill I have at work can barely start at 2400 RPM. It is only 4 years old, so I doubt the caps are bad. Based on that, I didn't think that a 1hp motor could spin a 70lb? rotor up to 1700 RPM before burning up.

    I'll search for your schematic lakeside. I'll let you know if I can't find it.
    Last edited by The Metal Butcher; 04-20-2021, 12:44 AM.
    21" Royersford Excelsior CamelBack Drillpress Restoration
    1943 Sidney 16x54 Lathe Restoration

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    • #17
      Click image for larger version

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      • #18
        The 1/2HP pony motor was 1740rpm Farm Duty ratio was 1 to 1 ,was pretty shocked it got the 15 hp it up to speed.I’m sure a 1 hp would have no issues,if I ever get around to building a permanent setup I will use a centrifugal clutch on pony motor.

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        • #19
          Hmm....

          In TTT's Stone Hammer Simple RPC thread, he talks about a centrifugal clutch. I found one that would probably work. It's well more than I want to pay though. It's also bi-directional engagement, though replacing the bearings with sprag bearings would solve that. Sounds like a lot of expense...
          21" Royersford Excelsior CamelBack Drillpress Restoration
          1943 Sidney 16x54 Lathe Restoration

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          • #20
            Originally posted by Captain K View Post
            Can't help on the rest of it but every a/c clutch I've ever pulled had a tapered hub. Not an insurmountable obstacle but something to consider.
            A clutch from a lawn mower would be heavy duty, 12VDC and a straight shaft.

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            • #21
              I did this on a smaller scale: 5HP idler started with a fractional HP pony and no clutch. I put a cord with a plug on the pony so I could plug it into a nearby 120v recipticle to start the whole thing. I used an old C-H contactor to energize the idler then unplugged the pony.
              Tom - Spotsylvania, VA

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              • #22
                I was wondering about centrifugal clutches like they use on go-karts
                25 miles north of Buffalo NY, USA

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                • #23
                  TMB, that kit is just an example of several kits available online, easily. And it doesn't matter who's kit you might get, the balance caps are gonna be different because you balance to suit the idler motor your using. a kit will get you up and running, and you can balance to suit better your idler motor. sure, you can upgrade parts, but this would be easier to get running than tinking around with a pony. and that kit does in fact have pf caps, as well as start caps.
                  if you wanna get technical & fussy about the thing you adjust the caps anyway, so whats in the kit don't matter a whole bunch

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                  • #24
                    Originally posted by deltap View Post
                    ............................ First check with your utility on what they require. Y delta and power factor correction, probably not on 15 hp. ..................
                    The handbook I have from Union Electric (now "Ameren"), our local powerco, states that the requirement for a soft start begins at 5 HP. Power factor correction is not required at all on single phase service, it is not even mentioned.

                    It's really whatever you can "get away with". If there was a problem, it would start with neighbors complaining to the power co, who would then investigate, and require you to change or face disconnection.
                    Last edited by J Tiers; 04-20-2021, 10:29 AM.
                    4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                    Keep eye on ball.
                    Hashim Khan

                    Everything not impossible is compulsory

                    "There's no pleasing these serpents"......Lewis Carroll

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                    • #25
                      Originally posted by nickel-city-fab View Post
                      I was wondering about centrifugal clutches like they use on go-karts
                      It seems like it would wear out a centrifugal clutch with it spinning all the time while disengaged. Most of the centrifugal clutches that I've seen just use a bronze bushing instead of a roller bearing. Otherwise like the idea.
                      OPEN EYES, OPEN EARS, OPEN MIND

                      THINK HARDER

                      BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

                      MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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                      • #26
                        Perhaps a one-way sprag clutch? Same thing they've had on lawnmowers since time began. The old Briggs mowers used ball bearings that rolled up into these ramps and grabbed in that one direction only when you pull the start rope. Bet you never saw one of those wear out... because they didn't.
                        25 miles north of Buffalo NY, USA

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                        • #27
                          Originally posted by bborr01 View Post

                          It seems like it would wear out a centrifugal clutch with it spinning all the time while disengaged. Most of the centrifugal clutches that I've seen just use a bronze bushing instead of a roller bearing. Otherwise like the idea.
                          This style of centrifugal would work great Drum on Idler and other mounted on Pony,2 separate components Alignment would be critical. Click image for larger version

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                          • #28
                            Centrifugal clutches stay engaged when they are up to speed,
                            even if the input power is taken away. Then they backdrive, as it were.

                            -D
                            DZER

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                            • #29
                              Originally posted by Doozer View Post
                              Centrifugal clutches stay engaged when they are up to speed,
                              even if the input power is taken away. Then they backdrive, as it were.
                              -D
                              None of the ones from go-karts or "chugs" that I ever dealt with would back-drive at all.

                              The way they were made, back-driving would make them disengage.
                              4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                              Keep eye on ball.
                              Hashim Khan

                              Everything not impossible is compulsory

                              "There's no pleasing these serpents"......Lewis Carroll

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                              • #30
                                Originally posted by Doozer View Post
                                Centrifugal clutches stay engaged when they are up to speed,
                                even if the input power is taken away. Then they backdrive, as it were.

                                -D
                                Not on this style.

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