600V 3-phase motor (milling machine) --> 240V operation

[Jester]

I have been on the lookout for a bench top mill for occasional use (should be a good compliment to my Emco 8 lathe). I found a local one for a reasonable price ($500) however it is powered by a 3 phase 600V motor. So I would either need a converter or replace the motor to single phase 240V.

Has anyone done this?

Converter or swap the motor?

Estimate $ for the conversion?

[H.O]

What's the rated power and speed of the existing motor? Is it wired in start (or wye) or delta configuration?

Is single phase 240 "all" you have available?

Although step-up inverters for 3-phase motors does exist they're not very common and I suspect their price to be pretty high because of that. It'll probably be cheaper to replace the motor.

[SeanB]

You could build a rotary converter, if all you have is the standard US 120V split phase supply, and make a high leg delta 3 phase supply for the motor. Otherwise if you have the motor specs a simple cheap appropriated inverter that is single phase 240VAC input and 3 phase 220VAC output will drive the motor if it can be changed from Y to delta, assuming it is Y connected for DOL 3 phase use.

All of course depends on the motor itself, we would need a model number and nameplate data off it to check.

[retrolefty]

I have been on the lookout for a bench top mill for occasional use (should be a good compliment to my Emco 8 lathe). I found a local one for a reasonable price ($500) however it is powered by a 3 phase 600V motor. So I would either need a converter or replace the motor to single phase 240V.

Has anyone done this?

Converter or swap the motor?

Estimate $ for the conversion?

 Swap the motor
 Estimate $ depends on the size of the motor which you didn't mention.

[jpanhalt]

I have switched several machine tools to 3-phase with VFD run off American single-phase 220V or 110V (depending on HP) or to DC with a speed controller (KB brand) runoff 110VAC.

It is a bit of a toss up.   VFD's have a definite lag before starting.   DC starts and stops almost instantly.   Since your mill is bench top, I suspect it is less than 2 HP, perhaps even less than 1 HP.

I would not mess with trying to replace the 600V, 3-phase supply, unless it has a purpose-made motor and another motor (e.g., a flange mount) will not fit.  If it is less than 1 HP, I would lean toward a DC conversion, if you can find a motor for a reasonable price with the right mount.  Price wise, a 3-phase motor with VFD will probably cost less, particularly if the motor is not fractional HP.

Another factor to consider is what type of speed control does the mill currently have.  If it is done by changing belts, I wound be even more resolved to go to a variable speed drive.   Changing belts gets awfully old on a mill.

Does your mill have power feeds (e.g., Servo feeds).   If it does, be sure to consider what line voltage they need.  If it doesn't, you will probably be adding power feeds and DRO.  Trying to stay with the 600V head will mean bringing different supplies for those additions.

John

[Jester]

John,

The present motor is 1.5HP

The DC conversion using the KB board may be a good solution. Ball park price for a motor and the KB controller?

[jpanhalt]

The trick is to find a motor.   The DC conversion was for a Prazi SD300 bench lathe.  Original motor was  1/3HP.  It was replaced with a 1/4 HP DC Baldor (like the AP7402).  Perfect fit -- actually smaller and allowed a chip cover and plenty of power.  Problem is current list price is $403 at Baldor.   The one I picked up was new and was only about $100 on eBay (more than 10 years ago).  The KB controller (KBIC model, open chassis) was also about $100.  They are also available on eBay and various other Internet sources.

Only you know what motors will fit.   Is it a standard frame or face mount?   Assuming it projects above the head, size per se shouldn't matter so long as they have the same mount.  What is its native RPM?

I would start with finding a suitable motor(s).  Look for 220 3-phase with similar RPM, as it is easier to slow it down than to speed it up, and compare to DC motors.   The DC motor will likely me more expensive, but that cost difference may be offset by the controller.  Except for one VFD that I got from KB, my other VFD's have been "new" off eBay of various recognizable brands.   

Be very careful of controllers that are "removed from a working environment." That only means the other machines around were working.  I got one once, and it was immediately obvious that it came from the one machine that wasn't working at time of removal -- a bunch of SCR's were blown and the power trace burned.

John

[Jester]

A couple of pictures of the existing motor:

[Koen]

Swap it, there's plenty of single-phase 1.5-3HP spares. Although you'll lose torque compared to three-phase.

A VFD is a nice solution when you also make use of very-variable speed, instant reverse, automatic tapping and stuff. For a manual mill with three-stage pulleys, buy an honest, simple, easy motor. You'll need to swap the belts anyway : milling calls for correct torque and speed.

[NiHaoMike]

Why would they bother going to 600V just for 1.5HP? 240V or even 120V can easily handle that.

[SeanB]

Buy a standard 3 phase 200VAC motor, and a 3HP inverter with 250VAC single phase input to drive it. That way speed control and lower losses over a very lossy single phase motor, which will run at blistering hot in single phase. The current single phase motors always run a lot hotter than an identical frame and power 3 phase one, and the torque is a lot lower as well, plus they have poor start up torque.

Any chance of popping that cover off, might be a set of taps in there to change it to lower voltage operation, and a label in the lid showing that as well. Cheaper than a new motor if that is so, as a 600V motor likely is just 2 380VAC coils in series per phase.

Lokks like Teco discontinued that motor, but here are the generic mounting and sizes, along with wiring types and connections. Worth reading first.

https://buy.tecowestinghouse.com/EcommerceFiles/Manuals/TWMC%20Instruction%20Manual_143%20to%20449%20frame.pdf

[eKretz]

High voltage motors are almost always configurable for different voltages. They are configured for whatever voltage the place using them has available. Industrial settings don't use a lot of 120 or 240V single phase for equipment (only for lights, etc.) - most places run 480V 3 phase for the equipment.

SeanB's suggestion would give the best results as far as machine use. 3 phase is better in most every way for machines, and vfd-powered 3 phase is very handy.

[johansen]

since the motor will have very little scrap value, you might as well try and rewire it for delta at a minimum. (338 volts)

or double Y for 300 volts.

it will be useable at 240v in either of those situations but it will only develop half of its nameplate hp.

you may be able to rewire it for double delta, which would be 166 volts. you would need a vfd programed for 166v/60hz.

[floobydust]

On some projects I have found surplus distribution transformers like 208V/480V/600V and used that (step-up) to convert mains for machines. It was the cheapest solution.

Changing the motor can get expensive because the motor starter also has to be modified/changed (FLA is higher now), along with the control transformer which was supplying contactors, switch lights and controls etc. so careful it's not just the motor that needs to be changed. I don't know this machine but mentioning some things overlooked.

The motor nameplate only shows 600v which doesn't look promising for taps down to 230/460V. An oddball motor.

[james_s]

Whether you use that motor or replace it with another, 3 phase with VFD is the way to go. My friends have a lot of older equipment at their shop and we've retrofitted numerous systems with VFDs. You get variable speed, soft start, you can even run many motors faster than 100% although you have to be careful not to go too high.

[Koen]

Keep in mind it's a benchtop manual mill for occasional use bought for a reasonable price.

[james_s]

Sure, but what does that have to do with it? I haven't looked lately but in the past I've bought small VFDs on ebay for something like $25. I have one along with a 3 phase motor I've been meaning to put on my crappy Chinese drill press so I can eliminate the stepped pulley system that requires manual belt moving to change the speed.

[Jester]

Sure, but what does that have to do with it? I haven't looked lately but in the past I've bought small VFDs on ebay for something like $25. I have one along with a 3 phase motor I've been meaning to put on my crappy Chinese drill press so I can eliminate the stepped pulley system that requires manual belt moving to change the speed.

James,  can you provide a link to one of these low cost VFD's?

[SeanB]

Me as well, looking for some cheap $25 ones on fleabay too.

[james_s]

Just search on ebay for Variable Frequency Drive, prices are all over the place, sometimes they go cheap, I've never paid more than $50 for one.

For example:
http://www.ebay.com/itm/Allen-Bradley-160-BA02NPS1P1Variable-speed-drive-/131905790415?
http://www.ebay.com/itm/Allen-Bradley-Powerflex-70-20AB9P6A2AYNNRNN-Adjustable-AC-Drive-2-3HP-/192174362281?
http://www.ebay.com/itm/Allen-Bradley-1305-AA08A-Adjustable-Frequency-AC-Drive-2HP-200-240-230V-3100VA-/192174348733?
http://www.ebay.com/itm/Allen-Bradley-1305-AA04A-Adjustable-Frequency-AC-Drive-1HP-200-240-230V-Lot-of-4-/192171605754?
http://www.ebay.com/itm/Industrial-frequency-inverter-ac-drives-G7-F7-JVOP-160-JV0P-160-60days-warranty-/221827480613?

Many of them that say 3 phase input will also accept single phase input so check the manual of any you are considering. You will also want to check that they will support the voltage and horsepower you need, the above ebay links are only examples of what's out there, I see many dozens of VFDs on ebay at any given time. I think I've bought about 5 of them for various things, of those one turned out to be scrap but the others worked fine.

I see now that there are some cheap Chinese VFDs available now. I'd be curious to see how horrid they are, maybe they're fine, I don't know. Personally I'd go with a used name brand unit over a new China one though.

[Jester]

Looks like all the VFD's in the links accept 3-phase input. Unless I can get an economical VFD that produces 3-phase from 240V single phase (this is for a home not a 3-phase industrial setting), I will likely have to find a new motor.

[james_s]

Many of them say 3 phase input but will in fact work when fed single phase, best to check the manuals. If I think about it I'll check the model of the little Omron VFD I have, it's made for 3 phase input but I run it off single phase 240V and it runs a 3 phase motor.

[johansen]

cheapest way to get this 600v motor running from a vfd is to buy a 480v vfd and connect your single phase ac line to the midpoint of the capacitors in the drive (the allen bradly 1305 units have two 400 volt capacitors in series, and the other side of your line goes to all three of the 3 phase line inputs, so that all 6 diodes share the current. of course they won't share it equally but its good enough.

program the vfd for 600v/60hz and you'll get full torque from your 600 volt motor up to 48 hz. above that torque will drop off. you might be able to get full nameplate hp from it but it will run very hot. however that is safe for short time intervals, because it takes time for the motor to get hot.

i recommend you provide auxilarary capacitors unless you intend to buy a 5hp vfd.

[Jester]

Is this the wiring your proposing?

[johansen]

yes, that is what i've done with my AB 1305 480v 2 hp drive.

mine has 4 capacitors in series parallel, if you find a 1hp or 1/2hp unit it might only have two in there. you should add more to run the drive at or near its full load rating. i don't remember what the rms amps through a voltage doubler is, so i can't give you a safe number.

usually when running a 3 phase drive from single phase, 50% derating is safe.

in this case though, in addition to that derating, about twice as many amps are flowing through half of the capacitor at any given time, so that's basically generating twice as much heat again. so that puts you at 25% nameplate capacity unless you add more capacitors.