Bob Swinney -- Phase converters

Bob, I've got a theory question I might put in practice, if I've got the right idea.
I have built a couple of low-horse RPCs. No problems there. As I study the "rotary transformer" theory, it seems to me that both schematically and practically, there should be absolutely no difference in using multiple lower-horsepower idlers than in using one larger one; perhaps it might matter that they all have the same pole arrangement and speed... but maybe not even then.
And it appears that there would be no benefit derived (or lost) from coupling them mechanically.
Am I on the right track?
I hope so, as I can buy spankin' new-in-box old stock 1-3HP motors for about 1/6th the price of NOS 5-7HP ones.
LLoyd

"Lloyd E. Sponenburgh" wrote:
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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.

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He cannot do it on his CNC mill.

Ignoramus16024 wrote:
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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.

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help. A
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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

Lloyd E. Sponenburgh wrote:
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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.

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Pete, if I understood Lloyd right, and I think that I heard the same thing a while ago from someone else, the BOSS controls really need all three phases to operate. And then from then on, all control circuitry is 220v or 110v based and thus you need extra relays and stuff just to operate the VFDs which usually use 10v for signaling.
Easy with a phase converter, hard with drives.
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It may not be so simple because contactors may be interlocked with one another in a way that requires 110 or 220v. (something like, the spindle must be running in order to move table, etc)
What you say is possible, but what is also possible is that it will not work due to interlocking etc.
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A good start can be found here.
http://igor.chudov.com/manuals/Bridgeport/BOSS/R2E4/Chapter-4.pdf
there is a power distribution schematic. It does not look very discouraging. But I would be leery of altering this mill.

Ignoramus26200 wrote:
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The axis drives are single phase.
As for control voltages, the VFD will accept a dry contact closure for run, and there is certainly a contactor controlling the spindle now that will readily provide that dry contact closure with 5 min of rewiring.
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I didn't see a schematic, all I saw was a mediocre block diagram.
Give me a VFD of an appropriate size for the spindle motor, and a couple hours and I'd have the machine happily running on a 240V 1ph input.

Ignoramus26200 wrote:
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Per your chapter 4, the two transformers are single phase, so they can each be wired to the 240V single phase supply and their taps set appropriatly.
The three phas goes only to the spindle motor start/reversing contactor. contacts from the start/reversing contactor can be used for the VFD control, or better yet, those contactors are most likely driven by smaller relays in the control and the contacts of those relays would be a better choice to use.
Either way, a $200 VFD and a couple hours work. Very simple.
Where was Lloyd located anyway? I've got some comp time to blow...
Pete C.

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Ok... but my 3HP RPC cost me $63, all up, including a brand new motor.
And you still told us "rewiring". Well... If I have to re-wire the cabinet anyway, why not get the machine working per stock, first. THEN mess with it, if it seems reasonable. I don't have any particular love for the old technology, but it's a good foundation to thoroughly understand how the hardware, electronics, and firmware interact.
BTW... I'm in Northeast Central Florida. (it's even cold here for the next two days). If you've got a spare 2HP VFD and the time, "come on DOWN!" <G>.
LLoyd

Lloyd E. Sponenburgh wrote:
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The "rewiring" is barely more than the power connections. The power inputs to the two transformers and the VFD, the connection from the VFD to the spindle motor, and the three wires for the control connection to the VFD.
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Yes, but I consider "mess with it" as retrofit for Mach3, not just rewire power and a VFD to get it running on single phase.
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Actually, I do have a spare 3HP VFD on hand (got two from Iggy, one is on my Bridgeport now), and some comp time available. Got any good dive sites in the area? On second though scratch the dive thing, it's cold and I loaned my dry suit to someone in my dive club.
I could stick the spare VFD in the priority mail pretty easily...

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That, I really appreciate, Pete. Thanks. How much?
I might take you up on that, because my goal really IS to overhaul this beautiful hunk'o'metal into a modern machine. But right now, I have the RPC, it IS outside my machine room (out in the compressor shack), and it works fine. So, all I have to do is move around a couple of harness wires to get the two transformers on one phase, and I should be (hope!) cutting metal.
The machine was presumably "in service" when they unplugged it to load on my trailer.
However, as you maintained -- If I ran it off a VFD, it would at least be quieter and more efficient. It will get one sooner or later.
One question, please. How's the "spin up time" on a VFD-powered motor that's triggered externally like you recommend, vs. a motor running on an extant 3-phase supply switched by a contactor? I don't know what the BOSS controller expects, in terms of wait time for expected RPM.
LLoyd

Lloyd E. Sponenburgh wrote:
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I got it from Iggy for $100 and figured I'd keep a spare on hand or for future projects. I could send it to you to try out if you want.
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If you already have the RPC up, you can certainly test the machine on it. The VFD is ultimitely where you want to go however.
Upgrading to a "modern machine" is certainly an involved project, but there are a lot of resources available these days.
I'm building up a small CNC plasma table based on Mach3 at the moment. I expect to have it completed in a month or two.
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Yep. I believe Driveswarehouse.com is a decent source.
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Spin up, spin down, dynamic braking, speeds, etc. are all programmable on a VFD. For your application you'd be looking at setting the VFD for 60hz output, and zero acceleration ramp (immediate full speed), and probably coast on stop to match the original performance since there is a brake in the machine.

Pete, if you can sit on that "test deal" for a few weeks, I'll probably take you up on it, and either return it or pay for it, as you choose after I'm done.
Right now, I'm busting out a 2-1/2" slab section, and re-forming for a 5" pour in and around where the new machine will sit. (one expenditure begets another... sigh...)
LLoyd

Lloyd E. Sponenburgh wrote:
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No problem, just delete the .DOH. to eamil me.

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How is the other one, working for you? Sounds like you are happy.
By the way I have more, some I can sell for cheap due to cosmetic damage.
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I am very happy with a VFD on my mill.
I wish I could put one on my lathe, but this 40 year old motor that is 220v only, has bad insulation and leaks through insulation if powered by a VFD.
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With a braking resistor, I programmed my mill to stop in 0.5 seconds with electric braking.

Ignoramus26200 wrote:
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It's working very nicely. Having it mounted on the wall next to the Bridgeport works just fine. The only times I change speed I'm also changing tooling so reaching over and entering a new fewquency works fine. Otherwise with the original Brideport switch feeding the fwd/rev inputs it's just as easy as normal.
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You should post what's available. Lloyd will be wanting one, probably other folks. Not sure if I need another at the moment since I don't have any more three phase machines.
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In a lot of ways they're better than having real three phase power.
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I bet a motor shop could re-varnish and bake that motor and get it in better shape. Adding a line reactor between it and the VFD might help. Or of course you could scroung a better motor.
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I just set mine to 1 sec start and 1 sec stop. 1 sec is certainly faster than the stock coast to a stop.

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Not sinusoidal or modified sine-wave output from the VFD? What leaks, where?
40 years ago, they were using sophisticated varnishes on magnet wire. That's way later than the leaky old cotton or silk days. Of that, I know. I worked in the research and testing lab for Florida Transitron in 1968-69, before 'Nam slapped me out of the work-force for a couple of years.
(and to paraphrase someone you might know personally... Used 3-phase motors are a dime-a-dozen <G>)
LLoyd

On 2009-01-21, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:
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Lloyd, used three phease motors are a dome a dozen. I brought home two yesterday, one cost me $10 and another $15, both 2 HP.
What is not as easy to find is a 2 speed motor.
My alternative is to put a 5 HP inverter duty motor (which I have, also 184T) in the lathe, and rewire the starting lever to operate the drive instead. I am not in a hurry to do it, since the lathe works as of now. I postponed it until I would understand it condition a little better.

On 2009-01-21, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:
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    Hmm ... I worked for the original Wakefield Transitron, and one in East Boston.
    What ever happened to them over the years?
    Enjoy,         DoN.