Bob Swinney -- Phase converters

I expect the efficiency is a bit lower with multiple motors due to accumulated losses in bearings and whatnot. The best way to go is to eliminate the need for three phase power as much as possible and use VFDs in the few cases where it isn't possibly. VFDs are more efficient and also much quieter than an RPC.

You can use a series of motors to get the capacity you need. If you want, you can do a sequenced start where one motor comes on line, use that one to start the second, the first two to start the third and so on. As long as the combined HP of the on line motors is significantly more than the newest one to come online, you can just run the new one as a pure 3 phase motor. Since you are starting them off the previous motors, you do not need to mechanically couple them. It does make sense to couple the first one or two to a single phase starting motor.

The downside of all this is the extra motors, extra switch> Bob, I've got a theory question I might put in practice, if I've got > the right idea.

Absolutely. No need to couple them mechanically.

I have a phase converter with two idlers, which has a lot of benefits and no drawbacks. My idlers are 10 and 7.5 HP respectively. Using a lot of 1-3 HP motors would be messy, but not really electrically infeasible.

What were you quoted on a 7.5 HP motor?

Would you be interested in a new Reliance 10 HP motor?

I do not think that in a HSM context, you need a new motor for an idler. Even used motors have thousands of hours of service ahead of them, and phase converter does not load the bearings with anything besides the weight of the rotor.

He cannot do it on his CNC mill.

As far as Im aware..and do this in my own HS...multiple motors simply add to the capacity.

My big 7.5hp Clausing 1500 didnt want to start on the 5hp RPC, but Id turn on the MasterMill and the HLVH, leave them running and the Clausing would fire right up.

Gunner

Whenever a Liberal utters the term "Common Sense approach"....grab your wallet, your ass, and your guns because the sombitch is about to do something damned nasty to all three of them.

Sure he can. If he were reasonable close to Dallas I'd offer to help. A lot of stuff takes three phase power but doesn't actually use it as three phase.

"Pete C." fired this volley in news:497509cc$0 $497$ snipped-for-privacy@unlimited.usenetmonster.com:

Unless I want to re-design the mill AND the controls, Iggy's right.

The motor on an R2E4 is constant-speed. Speed is controlled by valving air cylinders and brakes to control a variable-pitch sheave.

I _could_ re-design all the speed control circuitry and hardware so that it controlled a VFD, but it's a closed-loop system as it now exists, and it wouldn't be a simple re-work.

My goal right now is to get the machine full-up working _as_designed_, THEN think about an upgrade or retro-fit of the electronics.

In addition to that, it will take some re-wiring anyway, because the R2E3 and R2E4 main electronics supplies derive their power from two phases of the 3-phase, rather than only one.

LLoyd

Gunner Asch fired this volley in news: snipped-for-privacy@4ax.com:

Sure... "no load" is the operative principle, though. Both the other machines are acting as idlers. If you loaded the first two machines, I'll bet the third wouldn't start.

LLoyd

Ignoramus16024 fired this volley in news:4Mydne9-fuIlQunUnZ2dnUVZ snipped-for-privacy@giganews.com:

Might be, Iggy; How much? (and how to ship economically?) I love the old RE designs. They last forever. I have a 1968 RE 1HP TENV motor on a powder granulator that is still running as quiet and strong as it did new, and it's never had _anything_ done to it.

Are the 'new' ones as beefy as the 60's vintage motors? I re-painted the '68 one a while ago, and it weighed in at just under 90lb. A new one on another machine (of other manufacture; I think GE) weighed about 60.

Yes, I know I don't need 'new' motors, but I can get 3HP NEW Dayton motors for under $50, and with aggregate shipping, about $10 apiece to ship. I already have two (only one working as an RPC right now_), and they work fine with my 2HP spindle motor, even though the rotating mass on the new motors is MUCH lower than the older designs.

LLoyd

This is that sort of thing, in a cardboard crate (plywood bottom). TEFC motor. 10 HP.

$200 plus shipping, it is UPSable. Figure about 130 lbs weight.

This motor was never unbolted from plywood.

As I said, I think that if you look and find a used super cheap 10 HP motor, for say $40, you will be fine with it for your phase converter application, essentially forever. And no shipping to pay if you find locally, at some tired guy's warehouse, hidden in layers of dust and other crap. Given current economic environment, scrap price and general fear level, you should be able to do that.

But, if you want new, my offer will stand for a week or so.

I am pretty sure that it is over 100 lbs, with the box but the box is not much.

I would love to sell this motor to you, but in my honest opinion it is overkill for what you want. Find some garbage used motors and that will work just as well.

Just one more disclaimer, the motor I have is under a pile of stuff, and there is a very small chance that I either do not have it, or it is not 10 HP, but my memory is pretty good in this instance.

Ignoramus16024 fired this volley in news:SsednZTyKPC_v-jUnZ2dnUVZ snipped-for-privacy@giganews.com:

Thanks, Iggy. I'll pass, partly because of the distance, and partly because you're right -- if I really need a bigger unit, I can dig one up locally for a good price.

LLoyd

You'll probably have less kinetic energy stored in several small motors, assuming they all run at the same speed. Whether this matters or not is a subject of debate. I haven't formed an opinion on the subject, and it doesn't seem that anyone has tried it and published the results.

There was a discussion about it at RCM a few years ago:

I am pretty sure that your phase convertor will work with either one large idler motor or several small motors with the same total horsepower rating. But to say that there won't be any difference at all is going beyond the evidence we have, I think.

I'd be interested to hear what Bob has to say. Some day I may try this experiment, and if I do I'll post the results here.

Best wishes,

Chris

That assertion certainly bespeaks authority.

So, why do you think that they need to be coupled mechanically?

Ignoramus26200 fired this volley in news:MtednRLrj9yvTOjUnZ2dnUVZ snipped-for-privacy@giganews.com:

Iggy, I don't think that was the issue he was addressing. ;)

LLoyd

Chris sez:

" . . .I am pretty sure that your phase convertor will work with either one large idler motor or several small motors with the same total horsepower rating. But to say that there won't be any difference at all is going beyond the evidence we have, I think . . ."

Although I've never set up specific experiments substituting several small idlers for one large idler I am reasonably certain the difference, if any, is miniscule. I would think accumulated friction and windage losses from many small idlers would become objectionable only over a large number of idlers. Not likely to be problematical in quantities used in a home shop.

Problems with differing pole arrangements and speed is a non-issue. One might consider all the motors running in any 3-phase distribution system. Those motors, irrespective of speed, numbers of poles, even phase, are all interchanging current with each other on some level. That analogy is applicable to the entire grid.

Bob Swinney

You'll probably have less kinetic energy stored in several small motors, assuming they all run at the same speed. Whether this matters or not is a subject of debate. I haven't formed an opinion on the subject, and it doesn't seem that anyone has tried it and published the results.

There was a discussion about it at RCM a few years ago:

I'd be interested to hear what Bob has to say. Some day I may try this experiment, and if I do I'll post the results here.

Best wishes,

Chris

"Robert Swinney" fired this volley in news:mP-dnWaMjYpra-jUnZ2dnUVZ snipped-for-privacy@giganews.com:

Thanks, Bob. That's what I supposed, but don't have the power distribution experience to confirm it, except empirically.

LLoyd

Right!

Sorry for the delay in getting back to you, I've been having some news server / client issues.

You are thinking too complicated, it is really very, very simple.

The "two phases" feeding the controls simply connect to your 240V single phase feed with appropriate voltage tap adjustments.

The motor controls are nearly as simple. You locate the contactor currently controlling the three phase spindle motor, and disconnect the motor and power connection from it. Select one set of contacts on this contactor and they will connect to the run/stop input on the VFD (and it's control common). The VFD input power connects to your 240V single phase supply. The VFD output connects to the spindle motor.

When the control starts the spindle by closing the contactor, the VFD receives it's control input and starts the spindle motor. When the control stops the spindle, the VFD receives the control input and stops the spindle motor.

No changes to the speed controls are required. The speed continues to be controlled normally.

The only thing you rewire is the only thing in the machine that needs three phase power - the spindle motor. Nothing else in the maching needs three phase power, and the control only cares that the motor starts when it closes it's control contactor.

No noisy and inneficient RPC, just a small, silent VFD to stick on or in the control cabinet.

Pete C.