Driving an existing motor with a motor 2

[BrianGar]

I just bought a mill at a great price, its three phase, and to save buying another converter(I live miles from three phase) Im going to run this on single phase.

Due to the machines design the spindle motor frame is tailored to the machine, as is its mounting method.

So, to save messing(says he), and getting it rewound and all that, I intend mounting a single phase motor beside it, removing the fan off the three phase motor, fitting a pulley on there, and driving the quill with the single phase motor, through the existing three phase motor.

Its actually easier to pull off in reality that it sounds, which is why Im thinking strongly of doing it.

Now, onto the question...

Will I have to gut the three phase motor for fear the windings will cause drag, by generating current in some 'reverse way'?

Im pretty sure its a coil cage, and not magnets, actually, it defiantly is, so at the minute I cant see how it could cause a drag...but I know one thing, and that is, that copper is funny stuff when you move it around near Iron...

All I have to find out now is if the tail end of the three phase motor is turned down to within an inch of its life for the fan, that would be less than ideal if I intend mounting a pulley on there. Lets hope its not!

Many thanks

Brian,

 

[MikeHalloran]

That should work; just disconnect the 3ph motor from all power sources, and it becomes inert, save for a little air drag, which at ordinary spindle speeds won't be measurable.

These days it may be cheaper to just buy a variable speed drive for the 3ph motor; some of them will run just fine with a 1ph input.



Mike Halloran
Pembroke Pines, FL, USA

 

[BrianGar]

Mike, thanks for that.

I have a brand new single ph motor and a bunch of taper locks.

But, on looking at the whole setup again this morning with fresh eyes I starting to think more on what you said re variable drive.

Are the ones in the link below the kind I need? The motor is a 3hp.

Dad was saying something about if it needs a 'real' neutral as some converters only generate a false neutral. Do I also need a neutral generator? The site below also sells them. He lost me a bit with all the phase talk, he used to be a HT lines man for the ESB.

http://www.drivesdirect.co.uk/Products/Digital_Inverters240_415.htm

I can post up whats on the motor exactly if you need more info.

Many thanks,

BG

 

[BrianGar]

Just looking again at the site, it features an inbuilt brake, which would also mean I could do away with my air supply for the machines brake....interesting.

One last question, I take it its the fancy vector inverter I need, and not the basic one?

Thanks again,

BG

 

[fegenbush]

There is a small VFD on my local Craigslist, so you might want to check yours. Also, check any used motor sales/salvage companies. An acceptable unit for this use will be less than $200 in most areas. It is $100 in my area.

 

[BrianGar]

Is a VFD also a phase converter or just a 3phase vari drive?

Thanks,

BG

 

[badservo]

A VFD converts the AC (usually 3ph but can be 1ph) to DC, then converts it back to AC to drive the motor. Some VFDs cannot use 1ph input but most can (model dependent, read manual), you just need to use a larger HP drive. The input diodes and capacitors are under more stress when used on 1ph input, so you use a larger VFD to avoid running at rated output(for your app I would go 2x). Some small VFDs are sold as 1ph or 3ph input (see manual, may not need to oversize).

The VFD brake...
it only works to stop the motor, if you need to lock the spindle to change tooling then you will need the mechanical brake to hold it still.

 

[MikeHalloran]

As has been ably alluded, for milling, you don't need a fancy VFD, but you do need one with some 'cushion' re your motor size, e.g. a 5HP or maybe a 7.5HP unit, and _do_ go to the trouble of downloading the manual for any unit _before_ you buy it, wherein it will be documented that it can use a 1ph input, or not.




Mike Halloran
Pembroke Pines, FL, USA

 

[swall]

Even if one has 3 phase utility power nearby, it may not make economic sense to go that route. My power company wanted $1000 to run the line and then I would not have been allowed to retain single phase service. So, the shop would have required considerable re-wiring. 3 phase power also costs more. I went with a rotary phase converter (home made), as my Bridgeport, having a power feed motor, would have required 2 VFD's.

 

[BrianGar]

Well after a lot of looking and thinking I went for the single phase route. I had all the bits to pull it off, and stayed on till 11 last night to complete the job.

The end result is that I have what I need, it works great, and I still held onto my euros. The vari speed drive would have done it for sure, but that would mean picking the correct one, wiring it up, paying for it, and waiting for delivery.

I think I made the right choice considering, see picture attached,

Thanks guys, for all the advice, little bit of wiring to go and its done.

BG

 

[swall]

Nice job.

 

[MikeHalloran]

Damn, it looks like a factory adapter. Only better.
Star for that.


Mike Halloran
Pembroke Pines, FL, USA

 

[BrianGar]

Jeez Thanks Mike.

I knew Id use that bit of 15mm plate sometime.

Now just the 'minor' task of retro fitting the age old electronics and she'll be good to go.

The hurco km3s were some serious solid Iron thats for sure, twice as beefy as the bridgeports of the same footprint, plus, they are still in operation and answering support calls on old machines, which is, Impressive.

BG