Running multiple 3-phase motors?

[Doc Nickel]

I have a vague chance to buy a machine that uses multiple motors (for example; spindle, power feed, coolant, etc.) all of which are 3-phase. Everything is reasonably light; 2hp spindle, 1/6th hp coolant, etc.

What would be the best way to do that; a series of VFDs, just two VFDs (one spindle and one for everything else) or one big rotary phase converter.

Doc.

[Bguns]

Rotary is simplest.. Bulkiest also..

A cheap Static for PF and Pump, with VFD for Spindle is an option...

Multiple motors can be run w a Single VFD, but you run into lack of overload protection for smaller Motors.

A small Rotary for PF and Pump, is also a thought...

Cheap v/f VFD's for little loads, might be almost as cheap as a big home brew rotary...

Kind of depends on what your home built small Rotary parts pile looks like...

Got an extra 5hp 3 ph for an Idler? or a 1 hp for just Pump and Feed?

[rockrat]

Cant say that I'm an expert here but...

I have a 15hp rpc and it will run my lathe with coolant pump while I am running my mill. The rpc is quite big and since it is a 3k rpm motor, it works well as a buffer that I cant stall.

As for a VFD, I had always though that the rule was 1 VFD per motor but I cant say that I have really studied the subject.

If you have a large motor for an rpc then your half way there for free. I think that the rpc motor has to be the same horse or larger for startup. So if you had a 2hp spindle and a 1/2 horse coolant pump then a 5hp rpc should be fine.

rock~

[hardtail]

Was this a packaged unit originally? Or a franken machine of add ons later......LOL If it's the former you should only have to address the total hp requirements for the machine and it should be wired with current protection on it's auxilaries and distribution already, if the hp numbers get big you will have to oversize both the RPC idler by ~40% or allow for VFD derating.......Are you sure all the lesser loads are still 3 phase????

[Doc Nickel]

It's a "package", yes, but still separate motors. One control panel- not integral to the machine- operates each part, but does not "distribute" the actual power. Each part is wired- was wired, anyway- to it's own source, and the box just does the switching on and off.

Two of the motors are common-enough style and layout that I could pretty easily swap them for single-phase. Heck, I already have about two dozen suitable motors laying around.

But the spindle and coolant motors are specialized enough I either can't or won't swap (assuming I can get this thing, which is a long shot at best) so I was thinking I'd be best if I could simply provide 3Ph to everything.

I thought I'd heard that I could start one large rotary converter, and then run any number of motors (to a limit, anyway) normally after that.

As I recall, in that case you'd want to turn the largest motor on first (which would be the spindle) right? Would you then need to turn that one off first, or last?

And while I'm thinking about it, I had one other question about 3Ph: Is there any reason a 3Ph magnetic chuck, like the kind that goes on a surface grinder, couldn't be used with a rotary converter or VFD? And if one could use a VFD, how the heck would you size it properly- since the drives are typically labelled as to HP of the motor. How much power does a mag chuck draw, anyway?

Doc.

[derekm]

I have a 3 phase for the
lathe (1HP), mill (2HP and 1.25HP,separate motors for the Horizontal and vertical,) shaping machine(1Hp), coolant pump(1/8th) and the mill has a separate 3 phase feed motor(1/10th HP). And I will soon convert the drill press to 3 phase (1/2 Hp)
I have these 7 motors split that between 3 VFDs,

The smallest VFD for the 100w pump, which feeds all the tools flood coolant, ( it has to be able to run with everything else so it gets one to itself)
The next smallest for feed motor, and soon for the drill press. (The feed has to be separate from the main mill motors so I can drive it at a different speed and the drill press might be worked by someone else, if I'm using the lathe.)
and the biggest for all the rest. (i.e. both Mill motors, lathe, shaper)

The selection of tool to VFD is done by a relay bank.
A second relay bank governs the single phase to each VFD and the wall power sockets.
The relays are driven by 12V off a power supply backed up by a very small UPS.

The intention is to have a shop wide emergency stop and interlocks on reselecting while at speed etc... but at the moment its running on a "getcher going" set of low voltage switch gear to drive the relay banks.

All the relays and VFD courtesy of Ebay.

[JoeFin]

I run multiple 3 phase machines, each with multiple 3 phase motors all at the same time on a single RPC now. It doesn't bother them a bit.

Do all the normal stuff - occasionally feel the motor to insure it is not getting too hot and check the voltages to insure the motors are balanced loads

Besides - if this machine of multiple motors was run off multiple VFDs then you would have timing issues

[doctor demo]

And while I'm thinking about it, I had one other question about 3Ph: Is there any reason a 3Ph magnetic chuck, like the kind that goes on a surface grinder, couldn't be used with a rotary converter or VFD? And if one could use a VFD, how the heck would you size it properly- since the drives are typically labelled as to HP of the motor. How much power does a mag chuck draw, anyway?

Doc.

Doc, all the mag chucks that I have come in contact with are direct current.
My little one has a 5 amp fuse at the rectifier/controll box. 120v single phase in, 120v dc out.
I can't remember what the B&S 12x30 chuck uses for fuses , but it is 120v dc also.


Steve

[Bruce Griffing]

I use a Phase Perfect to run the whole shop. It will take a combined load of up to 10hp. It runs off the main panel and feeds its own three phase subpanel. I wired the shop with several three phase outlets. I do have some VFDs as well - where the variable speed is useful. If you can, buy a Phase Perfect once and be done with it. A very good, if a little expensive, solution.

[lunkenheimer]

Answer: it depends on what you need...

Not to belabor the obvious, but the service loads (coolant pumps etc.) should be on a steady supply since they shouldn't vary speed according to the load. The spindle load may benefit from a VFD, but generally the issue is what is the best/cheapest way to make 3 phase, and do you want speed control.

If you don't want speed control, use a single RPC to make three phase and be done. Otherwise, you may need an RPC for the coolant pumps etc, and a VFD for the spindle. This costs more, but provides spindle speed control, independent of the other loads, which generally should remain fixed.


Just my two bob worth....

[Doc Nickel]

Okay, to revisit an old thread: I didn't get the surface grinder I was referring to here, which had a spindle motor, hydraulic pump, coolant pump and vacuum blower.

I did, however, just get a Republic-Lagun surface grinder that has the same issue; spindle motor, coolant pump and vacuum, all separate motors, all 3-phase.

The coolant pump is a 1/8th HP, the fan is 1/3rd, and the spindle I think is 1HP.

So we've gone from a theoretical issue to a practical. I have no "spare" 3ph motors (and none at all over 2HP) with which to build an RPC. Would my best bet be to buy, say, a 3HP RPC (almost $600 from ENCO- ouch!) and run the works off of it?

I don't need more than that- all the other machines already have their VFDs where applicable. A $2K Phase Perfect is also pretty much out of the question.

Of course, for the $600 (plus shipping!) RPC, I could buy two small VFDs and be ahead of the game.

So maybe I should look for a cheap surplus 3 or 5hp 3-phase motor to make my own RPC...?

Doc.

[wierdscience]

Well me I would go for the surplus motor/homebrew RPC route.

Nothing on that machine would benifit from variable speed so a VFD would be a waste.

You only need a motor the same size as or slightly larger than the largest motor on the machine to run all three at once.Just wire them so the main motor comes on first and the other two are switched on after.The main will become an RPC for the blower motor and it will become an RPC for the coolant pump motor.

I had an old Yates woodworking moulder that ran 6,3hp motors.One 10hp RPC was enough to carry all of them so long as they were started up one at a time.

[J Tiers]

Just to back up a little..... and not be totally specific to that machine.

A static "converter" is definitely sized to ONE motor, and is really not suited to run multiple motors. You wouldn't put one start circuit on multiple single phase motors, and that's all a static is.

However, a static if it starts ONE larger motor, which runs all the time, can then run several smaller motors which are turned on and off. it just may not provide very good balance, depending.

So......

Assess what motors will run the longest time, and what will turn on and off, if any.

Assess what motor really needs good 3 phase, if any. That would be your spindle.

See if any motors need variable speed. I suspect none, in your case,the machine would run great off wall 3 phase.

So, you have your choices.

You could run the lot off an RPC. No reason not to, except that you don't have one.

You could run the lot off a VFD, and would probably be fine letting the VFD just make 3 phase at 60 Hz, no variable involved, except for a ramp-up to avoid an overload at start.

If you turn the low power ones off and on while the spindle keeps running, that still likely won't bother the VFD.... if they are quite a bit smaller.

if either is of more equal size to the spindle, like 1/3 or more the power, I think I'd lean toward the RPC. I doubt you really need the VF part of the VFD, you really just want 3 phase. And turning off and on a closer-sized motor would be a strain on the VFD, plus having more "spike energy" potentially dumped back in.

Either way you would be well advised to fuse the low power motors so that they have less chance of burning out in case they stall for some reason. I don't think I'd bother with individual starter/overloads for them.

[Doc Nickel]

I doubt you really need the VF part of the VFD, you really just want 3 phase.

-Exactly. Can't imagine why I'd want a variable on the spindle, though I was thinking a variable on the vacuum motor might be handy- turn it down a bit to reduce noise when grinding small pieces, maybe.

Probably not necessary, just something to think of.

Really I just need "inexpensive". A static is cheap- relatively- but we lose a third of our motor HP. Probably no big deal on the spindle or vac, but might be an issue on the already-teeny 1/8th HP coolant pump.

Then again, I wonder about vibration issues, running the 3Ph spindle motor on two phases. Again, may not be an issue, but still something to keep in mind.

I'll start putting some feelers out for a spare 3-phase motor. Should I look for a 1725 or 3450 rpm? Or does it matter? And what would be better- a 1 or 2 HP, or a 3HP or more?

Doc.

[wierdscience]

-Exactly. Can't imagine why I'd want a variable on the spindle, though I was thinking a variable on the vacuum motor might be handy- turn it down a bit to reduce noise when grinding small pieces, maybe.

Probably not necessary, just something to think of.

Really I just need "inexpensive". A static is cheap- relatively- but we lose a third of our motor HP. Probably no big deal on the spindle or vac, but might be an issue on the already-teeny 1/8th HP coolant pump.


Then again, I wonder about vibration issues, running the 3Ph spindle motor on two phases. Again, may not be an issue, but still something to keep in mind.

An RPC would be better,not as much power loss and all three phases see voltage.

-I'll start putting some feelers out for a spare 3-phase motor. Should I look for a 1725 or 3450 rpm? Or does it matter? And what would be better- a 1 or 2 HP, or a 3HP or more?

Doc.

1800RPM 3-5 would be my pick.The extra mass of the lower speed rotor will help with starting.

But,there is also this option-

http://phoenixphaseconverters.com/category.php?id_category=6