Replace a 3 phase motor with single phase; equivalent power?

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Andy Birko
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Andy Birko »

Mario Proulx wrote:The school looked into having it converted, and it was well over 3 grand.
I have no intention of turning you to the dark side ( :D ) but, that >$3k figure is probably a figure for a turn key servo kit or something like that. A DIY conversion could be done for easily well under $500 for a NEMA 34 (a guess as to the motor size) two axis stepper setup. Control computers can usually be found in dumpsters and control software like EMC2 is free.

Again, I'm not trying to suck you in to CNC but for the record, readers should know that CNC can be done for a lot less money than one would think if you can spend just a little time doing it.
PMoMC
Ron Belanger
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Ron Belanger »

Hey, nice looking lathe Mario. Good luck with it.
Mario Proulx
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Mario Proulx »

Here's the motor's wiring innards... Hope this tells us something?

Yes, it has a capacitor, and yes, there's a centrifugal something or other that gives an audible "click" while spinning down.

Gettin' the itch to turn somethin'.... ;)
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Nelson Palen
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Nelson Palen »

David, you presented enough evidence to make a believer out of this old man. Makes sense to me now and interesting discussion.
Nelson
Mario Proulx
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Mario Proulx »

D'oh! Here's the image....
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Mario Proulx
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Mario Proulx »

Got her up and running last night! The fella who gave me the motor said he was sure it was setup for 110, and he agreed that there's no harm in running a motor on 110 if it was setup for 220 anyhow(other than it putting out only 1/4 of the power.

Runs like a champ, except if I try to run the lathe at its highest speed, which is 2,000 rpm. It does fine at 1,000 rpm, but the next gear up is 2,000, and it can't get it up to speed, with the motor doing the click-click-click thing with the centrifugal switch kicking in and out. Not enough grunt for this lathe, or is this telling us it is indeed setup for 220v?

Other than that, the lathe seems to work fine. The threading indicator dial thing was seized, so I took that off and fixed it(just needed some TLC). All other feeds work flawlessly.

Oh, and yes, it had a separate motor for the Z axis; there's a lever at the main gearbox that would disengage it, leaving the stepper or servo motor to run the show. I've removed all of that....

Only disappointment so far is that I just realized last night that the entire lathe is Metric. Arghhh! I hates metric.... I appear to have the extra gear sets necessary to cut inch threads, but the handwheels are all marked in mm, not thousandth's... Oh well, not the end of the world.
Louie Atienza
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Louie Atienza »

What a great lathe! I'm jealous... Alas with metric, but I'm sure you can divide by .03937 in your head?!
David King
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by David King »

I would have serious regrets going to single phase on a metal lathe as there are many times it's nice to be able to throw the lathe into reverse and not have to wait the 10 seconds for the motor to spin down to a dead stop first. The 550V would present a problem but there are three possible solutions, one is to run your 240V line through a 3kva, single phase 550v stepup transformer and then into a 3 hp 550V VFD to generate the two remaining legs. The 550V VFDs go for surprisingly little used as the majority of industrial motors are either 208V or 440V. Next option would be to run a 3-5HP, 220V rotary phase converter and step that up through a 3 phase, 3kva 220-550V transformer. A 3kva transformer would be the minimum size but often the larger xformers will sell for less. I found a nice used 3ph 220-440 9kva transformer for $150 on my local craislist, about 1/3 the cost of a new 3kva unit. I saw 30kvas going for $100 on ebay just because they are so heavy to ship.
Check out ebay and HGR ( http://www.hgrinc.com/ ) along with your local motor repair shops. A home built rotary phase converter is quite affordable if you can find the motor used in the scrap pile locally. A lot more folks want to replace 3 phase motors with single phase than the other way around. A 550V RPC might actually cost you the least as it will have the smallest amount of copper in it and you can use 18AWG to wire it up.
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by David King »

Regarding the metric, you can either pickup a digital read out (DRO) that will read actual part diameter and carriage position and ignore the dials or replace the lead screws and nuts with their US equivalents. Most of us just figure .025mm is more or less equal to .001" and keep a digital caliper handy to do the fine math for us. Once you get used to mm you'll find them much more convenient anyway.

There are several open-source DRO systems available that will cost a fraction of the name brand ones and will have expandable capabilities far more advanced than what you can dream of. Check out Shumatech and VDRO. You can use the cheap capacitative scales by cutting up Chinese digital calipers (harbor freight) or get magnetic ones with remote readers like iGaging/Wixey (Quint). For a reliable/professional DRO you will want glass scales, the ones from Ditron in China only cost a few $ more that the capacitative or magnetic scales and will be way more reliable and accurate over the long run.
David Malicky
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by David Malicky »

Well, it's definitely not setup for 220, but I'm not sure if it's setup correctly for 110, either. I'm not an electrician, nor a motor expert, so hopefully someone else could give better info.

In the pic, each of the Line inputs ("L") appears to be connected to 3 other wires:
Line on the left is connected to:
- a wire from a bent-inward tab, going into the motor casing (above the nut, not visible in pic). Is there indeed a wire here?
- Terminal 5 (screw)
- Terminal ___ (other screw) Is there a number under one of the plates?
- The Black wire, which should go to the start circuit/windings

Line on the right is connected to:
- a wire from a bent-inward tab, going into the motor casing (above the nut, not visible in pic). Confirm there is a wire here?
- Terminal 2 (screw)
- Terminal 3 (screw)
- The Red wire, which should go to the other end of the start circuit/windings

So the windings are clearly not wired in series, so it is not wired for high voltage (220). BUT, the connections and numbers do not exactly correspond to the NEMA standard diagram on pages 8-9 of the link I gave before. The main difference is NEMA never connects 2 and 3 for low voltage (110), whereas they are bridged in yours. Possibly, the motor isn't following NEMA. I did find a similar diagram to yours, though, Fig 4 here:
http://www.metalwebnews.com/howto/elec- ... c-mtr.html

With a dental mirror and flashlight, can you check the wire colors going to each of the terminals, on the back of the plate? That should help figure out who is who.

On the problem getting to 2000rpm, it seems unlikely that speed w/ no cutting load would require more than 1 HP. It sounds like, on startup, once the start winding disengages (click), the run winding is unable to *even maintain* that speed, so speed drops, the start winding clicks back in, repeat. Does that sound consistent with what you see? For sure, there is a max torque dropoff above the click, but it should still have at least 200% of its rated torque at that point.

I can think of a few causes:
1. A problem with the run windings. Possibly, only 1 leg of the run winding is producing torque, which would explain how it is feeble above the click. This could be shorted insulation, or simply miswired (above).
2. The centrifugal switch is cutting the start winding out at too low an rpm. Unlikely, though it's possible if a spring is weak.
3. The gearbox oil is very viscous, or some other drag in the drivetrain in that gear.

Instant reverse is indeed nice. DC with the right controller can also do it. If 3PH, I'd favor a 220V 3PH motor and VFD. Motors are less than $100 on ebay. Locally, a lot less. Older VFDs aren't much either. The least $ solution I know of is to find a broken treadmill: Usually 2HP DC motor and matched controller, often for free. That controller can't instant reverse, though one that can is about $50.

On metric, yes, a DRO of any kind, at least for the X-axis, is the best solution by far. Even it were already English, a DRO is the best solution by far! So metric gives you even more reason to go DRO. Outside of that, for that Logan, I made a new cross-slide screw using precision acme... not too hard, especially if you happen to have a... lathe?
Mario Proulx
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Mario Proulx »

Thanks for all the help! As of now, I'm happy with how it's performing(I've already made good use of it!), and really need to get back to my normal life of building instruments and pickguards....

On the subject of 3 phase: I'm not at all concerned with finish appearance; I build instruments for a living, and the lathe is here to help me refine jigs, tools, and repair the odd thingie here and there. I'm not making a hobby of it, so as long as it spins, I'd rather spend any money I will spend on tooling. And I cannot think of one operation where I'd want to reverse the motor, much less instantly. Name a few?

Edit: yes, your description of 2000 rpm startup issue is spot on. I hadn't considered a weak spring, but that makes perfect sense. When I decide the lathe's final destination, I'll be hard-wiring it all, and will pull the motor then and maybe open it up. That way, I'll check the springs and also see the wiring clearly. Also want to check the bearings at that time, as they could be smoother....
Halgeir Wold
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Halgeir Wold »

OOOH - Metric is comin'.... :lol: <ducking....>
Good luck with the lathe, Mario.... a more suitable moter may surface, just out of the blue.....
Dick (DT) Trottier
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Dick (DT) Trottier »

Hi Mario,

If you want to try wiring for 220V: 1. measure resistance L to L, 2. remove the left jumper bar completely. 3. undo the right jumper bar and connect it across the two top terminals. If your L-L resistance is now 4 times higher you're good to go.

Good luck...
David King
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by David King »

Mario, you won't miss the reverse if you never had it. Reverse on the fly is generally a braking strategy to save time and fingers. If you are machining repetitive parts when you need to chuck and un-chuck repeatedly for a single operation you'll really come to appreciate it. Also when threading a shaft up to a flange or wall, it's handy to stop the lathe on a dime if you don't have a fancy, spring-loaded cutter holder.
If you get into repetitive parts you'll probably start looking for a lever-action collet opener so you never have to stop the lathe at all. A jerry-rigged bar feeder is all you'll need.
Mario Proulx
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Mario Proulx »

Thanks for clarifying the reverse-deal. I couldn't imagine any turning operation where you want to rotate in reverse..... As I said, though, I'm not going to produce anything in numbers on the thing; it's mainly just another tool to help me build, maintain and modify tools to help me build better instruments. I was prepared to put a brake on it, as I have a nice small hydraulic disc setup off a quad that could easily enough be fitted to the main shaft, but it comes to a stop within seconds anyhow, so it's not an issue. I can see where an instant brake would be a safety thing, though. Maybe add the brake, and a motor cutoff(magnetic switch?) to a full-length-of-the-lathe brake pedal.

Dick, to clarify(because when I do move the lathe and hard-wire it, going 220 will make sense), you're telling me to disconnect 4 and 5 from each other, and disconnect 2 and 3 from each other, and connect 3 and 4 together, right?
David Malicky
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by David Malicky »

Other uses for reverse: backing the tap out after power-tapping with the tailstock, getting a drill bit unstuck that's in deep and packed with chips, cutting angles with the compound (often better access), cutting internal grooves so you can see better, cutting external threads by leaving the half-nuts engaged (essential when the threads are english and the leadscrew is metric, or v-v), and making the dust go away from you and the ways when sanding. The camlock chuck was a boon to reversing, or at least to much safer reversing! Your motor can probably be reversed by swapping those red and black wires.

Yeah, a brake pedal is great.
Halgeir Wold
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Halgeir Wold »

David Malicky wrote:Other uses for reverse:
For lack of coil winding machine, I've used the lathe on several occasions..... ;)

Just a question - I'm not a machinist by trade ( electronics/ electrics) - but aren't most reverse functions in the gearbox, rather than electrical?
It certainly is on the not-so-many lathes I've been using... - mostly 70s and early 80s models' I'll admit........
Dick (DT) Trottier
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Dick (DT) Trottier »

Hi Mario,

That's correct. One thing to note is that the start winding is low voltage regardless of whether you choose to run at the low or the high voltage. What you'll end up with is one 'L' (right in the picture) going to a run winding, the other 'L' (left) going to the other run winding and a start winding. The other end of all three windings tie together, putting the run windings in series and the start winding in parallel with one run winding.

Do check those resistance values just to be sure before powering it up.

Good luck...
David Malicky
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by David Malicky »

Good one, Halgeir!

Usually spindle reverse is done electrically, often by a forward-off-reverse lever on the carriage. Some higher-end lathes, mostly European I think, did instant spindle reverse via a clutch-pack and gears on an additional layshaft in the headstock. Curious what lathes have you seen it on?
Halgeir Wold
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Re: Replace a 3 phase motor with single phase; equivalent power?

Post by Halgeir Wold »

I don't recall the names of the few ancient ones I've been in contact with, but the one I've used the most is the english Colchester 3000 ( ca 1970) which we have at work..... the forward-reverse is as you say by a lever on the main carriage, which also has a clutch function. The motor and pump are on different switches...
THis is a strictly manual lathe. I've never used CNC lathes........
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