Just bought "new" lathe - questions about powering with VFD??

I just picked up a nice used Acer 1440G lathe like this...


It will be used in my garage which provides only single phase power. I already have a Bridgeport mill in my garage, which is powered with a VFD that I wired up without any problems. My Bridgeport's VFD is wired so that it never experiences a zero load condition on its output which, from what I read, will quickly destroy a VFD. With the VFD output wired directly into the motor, this hasn't been a problem on my Bridgeport. Here is the bascis schematic I used on my Bridgeport:

single phase 220VAC from breaker box----> E-stop switch--->input to VFD----->VFD outputs 3 phase 220VAC---->Bridgeport 1-1/2hp motor.

But now I have this new machine and it has an integrated on/off switch built into the carriage/apron/saddle and also an integrated e-stop button. So offhand, I don't see how I can easily connect a VFD to the machine's power input without risking a zero load condition. Any ideas on how to approach this problem so that the lathe can be fully used the way it is intended?

You rewire the e-stop and power switch from the lathe so that they control the VFD using its analog inputs.

Teryk

Yep just use the controls to give the VFD commands and it will work as if it were using the original controls. But you will have variable speed.

There is no reason to worry about a zero load.... that is not going to destroy any VFD I know of. Maybe there is some odd type that would be damaged, but not any standard type I have seen.

What IS a problem is if you turn off a motor with a switch on the output of a VFD that is matched to the motor HP, and then want to start the motor by switching on again. You can get away with that if the VFD has a current rating at least 4 or 5 times the motor FLA, but a matched size VFD will go into current limit (overload).

Some say that just the turnoff itself can damage a VFD. Again, not any types that I know of, but maybe there are some old types that can be damaged by that. If the manufacturer warns against it, maybe they know of some vulnerability of their particular unit.

None of the ones I have worked with, or designed, have had any actual or theoretical problem with such turn-off. But, as mentioned above, there is little point unless you can also turn the motor on that way, and usually that is not going to work.

Maschine said:

Any ideas on how to approach this problem so that the lathe can be fully used the way it is intended?

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If "the way it was intended" never had a VFD to begin with, WTH is wrong with running it off an RPC instead of a VFD and not having to change any on-machine wiring at all?

Monarchist said:

If "the way it was intended" never had a VFD to begin with, WTH is wrong with running it off an RPC instead of a VFD and not having to change any on-machine wiring at all?

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I agree. But apparently an RPC is just way to old fashioned now.

I do not agree that VFDs are a simple install as outlined for a lathe and keeping all the safety features, you also have issues with using the mechanical foot brake. It is possible to strip out the high voltage to the forward reverse contactors and use them to them to switch the Forward, Reverse VFD inputs. I wire the E-Stop with two NC contacts, one side disconnects the 24VAC power, the other the VFD inputs. In addition I wire in a dual pole (NC and NO) foot limit switch witch issues a free run command to the VFD in addition to tripping the 24VAC power relay when the brake is depressed. Not and ideal situation to use contactors for low level VFD signaling, but works if they are new. Otherwise I usually do a full control system rebuild. You also need a braking resistor for the VFD and some higher level programming to get the most out of the VFD.

An RPC is more plug and play, the lathe will work as it is suppose to do. If you want the variable speed from a VFD, then it is a more extensive design for a lathe if you care about safety.

Just bought "new" lathe - questions about powering with VFD??

Everyone and their brother makes a drive now, and it’s hard to tell what you are getting unless you spend some money and go with a well known brand.
I didn’t watch the video, but once you get onto the 5hp+ drives , single phase input options become limited. Electrical power is electrical power and it needs to be transmitted over appropriate size conductors, so if the “5hp” drive that you buy is the size of a Rubix Cube, don’t expect it to last long.
I’m in the same boat re single phase 220 input and a 3.7Kw (5hp) 3 phase lathe. I’m pretty sure I’m going with an American Rotary AR10 rotary 10hp converter, $840 if you buy their 3phase breaker. $740 without.

The above post has some real good points. Properly converting a lathe to a VFD is not rocket science, but requires some solid electrical theory and print reading(or wire tracing) ability.
The last thing you want is an improperly wired drive that won’t stop, or does other unintended things

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Also consider minor things like 3 phase coolant pumps, are you going to run it off the VFD? If so it will be getting the same frequency and phasing as the main motor( maybe running backwards or at reduced speeds/flow)


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Thanks for the responses everyone. I'm actually fairly electrically savvy and am not too intimidated with a little wiring project for a VFD. And I DO definitely want all of the safety features to function perfectly and for the lathe to run like it does on normal 3 phase wall power.

But maybe I should consider an old school RPC? I could use it to power both of my machines because they would never be used at the same time. And since they're both already variable speed (freshly rebuilt variable speed head on the Bridgeport and gear ranges available on the lathe), don’t think I'd be giving up much in terms of speed variation. I've never owned an RPC though and I opted for a VFD for my Bridgeport because I got it cheap and I also thought I heard the RPC's were loud. I do NOT like unnecessary noise in my shop (having hearing loss already caused by industrial noise). So I guess my question is, can the RPC be made to run quiet? If so, I might just do that instead, because a quality VFD isn’t cheap, and I see used RPCs selling on craigslist for pretty good prices. In fact, the guy that sold me this lathe was selling one, but I passed on it.

This lathe also has a coolant pump, a light and I think it has an electronic control that maintains constant speed during a cut.

Maschine said:

Thanks for the responses everyone. I'm actually fairly electrically savvy and am not too intimidated with a little wiring project for a VFD. And I DO definitely want all of the safety features to function perfectly and for the lathe to run like it does on normal 3 phase wall power.

But maybe I should consider an old school RPC? I could use it to power both of my machines because they would never be used at the same time. And since they're both already variable speed (freshly rebuilt variable speed head on the Bridgeport and gear ranges available on the lathe), don’t think I'd be giving up much in terms of speed variation. I've never owned an RPC though and I opted for a VFD for my Bridgeport because I got it cheap and I also thought I heard the RPC's were loud.

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Running a VFD too far from its load is discouraged for several reasons that don't need covered yet-another-time just now.

An RPC, OTOH, doesn't OWN any fast-switching EMI/RFI generating sensitive electronics, can be remoted several hundred feet for no more hassle than the cost of decent wire.

I could as easily bury my 10 HP one in a backyard "bunker" or put it in the garage / shop annex attic. It isn't really that noisy. So I have not. It will probably get parked t'other side of the shop North wall, in a dog-house next to the Air Conditioner, my far noisier air-compressor alongside them.

FWIW-not-much-dept, I have TWO 10 HP Phase-Perfect, and several of my machines are Dee Cee anyway. Also a 10-15 KW Diesel gen set with 3-Phase, nominal 208 Wye, 220 Wye capable at the flick of a switch and twist of a voltage-control knob.

And yet .....I still have a 10 HP RPC.

Whyso?

Partly 'coz it is rugged-dumb, idiot-resistant hard to harm, more easily made "portable" than I care to do or risk with a far costlier Phase-Perfect that is lighter, but not really any smaller. Latch it to a cheap HF hand-truck, and away it goes, cordsets, outlets, disconnects, controls, and all.

I'd say START with an RPC for simplicity, flexibility, durability, universality of use with any load it can haul w/o diddling about with wiring or even the nuisance of re-programming.

Pick your next VFD only if/as/when you have a machine it provides a significant advantage to .... an advantage that you can actually make USE of. Even the Bee Pee didn't really need one. Most of them out in the wild don't have VFD and don't notice any disadvantage to that.

RPCs do not have to be loud. Get a 1725 or 1140 rpm unit and it will be quieter. Stay away from 3450 rpm units, unless you put it farther away.

RPCs are no more old fashioned than the lathe..... and the darn things are nearly bullet proof. They do not care about voltage spikes, loading, temperatures (within reason) , etc. They pretty much just work. And are repairable, at worst needing another idler motor from the junkyard.

VFDs have a lot of nice features..... but they are chock full of electronic parts, and the cheaper ones vary from "basic but OK", to "trash". LOTS of things that can go bad. Although they don't often fail, they are usually non repairable at a reasonable cost if they do.

The Acer 1440G uses a 3Hp main motor, so there are plenty of affordable name brand VFDs for this size Hp motor. The 3 phase coolant pump can be replaced with single phase or you could get an inexpensive KB VFD to separately run it. Looking at the circuit schematic, it does not show the input power going to the coolant contactor/transformer, this would need to be connected to the RS terminals after the 30A fuses. The coolant contactor overload relay can be reconfigured for a single phase coolant pump or get an inexpensive KB VFD for under $100. As mentioned it is an easy matter strip the RST high voltage wiring from the forward/reverse contactors and use them to switch the VFD inputs. The lathe will work exactly as the factory design with all safety features, as you retain the 24VAC circuity. I have a more detailed file on the conversion that has been used on numerous other 1440 lathes, but the file is too big to load here, if interested PM me with an email address and I Will send it to you. It also includes the brake switch and I can provide you with a generic programming file for the Hitachi WJ200 VFD. You are looking at probably $500-600 to do the VFD conversion, it is not complicated. You need a braking resistor and cannot get too aggressive with the VFD braking (less than 3 seconds).

I do a lot of lathe VFD conversions from simple to full builds, there are significant advantages to using a VFD on a lathe. I constantly dial in the sweet speed spot for different materials on the fly, I usually only switch the gear box from low to high and the VFD does everything else. In sensorless vector mode, the VFD maintains RPM independent of the load (+/- 1 RPM on my lathe). I have done a number of machinery VFD conversions for shops with 3 phase RPC's, because there was a distinct advantage to the VFD speed control, electronic braking and other programmable inputs. So a number of different approaches one can take. A well designed RPC can be very quiet, so this is also a simple conversion.

On the mill, why change anything if it works.

Simple VFD conversion using the contactor to switch the VFD forward/reverse inputs.I also recommend re configuring the manual brake switch and E-Stop connections as previously mentioned.

Jim aka PhaseCraft is a PM member. I don’t know how you can get 3 phase much cheaper than one of his panels and a used motor .

My idler is in a small shed outside with the compressor. I can barely hear it if I’m trying. One RPC powers my whole shop.

Adwcali said:

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Jim aka PhaseCraft is a PM member. I don’t know how you can get 3 phase much cheaper than one of his panels and a used motor .

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I bought mine from him - plus a brand-new Weg, (Brazil, not China) 10 HP motor, elsewhere. Even though ....I had ALL of the needful parts to build more than one RPC starter/controller lying about, and already paid for.

Some years, one has to put that ever-scarce TIME into other stuff that you CANNOT buy or hire done, and Jim's boxes are solid-reliable. Plus HE is ever-helpful.

Monarchist said:

I bought mine from him - plus a brand-new Weg, (Brazil, not China) 10 HP motor, elsewhere. Even though ....I had ALL of the needful parts to build more than one RPC starter/controller lying about, and already paid for.

Some years, one has to put that ever-scarce TIME into other stuff that you CANNOT buy or hire done, and Jim's boxes are solid-reliable. Plus HE is ever-helpful.

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I don’t get paid much for working on my own projects so I figure I’m way ahead paying Jim the little he asks for his panel. I lucked into a good used motor for $50, so I have less than $250 in my RPC that’s been quietly doing the job for three years now.

Wow, ok so maybe a RPC is a good idea for me? But like I said, I want a quiet one. So apparently if I did go the route of the RPC I would need a low rpm 3 phase motor in the right hp range? (in addition to either my own converter or simply buy one of Jim's). Any ideas what type of machines the low rpm versions would typically be installed on? And where would be the best place to find one?

On a lathe you typically double or more the RPC idler motor size, so maybe a 7.5hp. I don’t recall seeing many 6hp around, 5hp May get you by


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Maschine said:

Wow, ok so maybe a RPC is a good idea for me? But like I said, I want a quiet one. So apparently if I did go the route of the RPC I would need a low rpm 3 phase motor in the right hp range? (in addition to either my own converter or simply buy one of Jim's). Any ideas what type of machines the low rpm versions would typically be installed on? And where would be the best place to find one?

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I - and many others - use common 4-pole nominal 1750 RPM open-drip-proof, TEFC (Totally Enclosed, Fan Over), and now and then, the physically bulkier TENV (Totally Enclosed, Non Ventilated) motors as idlers.

Radiated noise "usually, generally" drops and at least "new" cost goes up in the order I listed those housing types.

Two-pole, nominal 3450 RPM are noisier, slower 6 and 8 pole are quieter but costlier new, harder to find used. One supposes that an array of 12 or 24 pole fractional HP ceiling fan motors, no blades, could be the quietest of all.

Really? Any big old TENV @ 1750 RPM is just not going to be all that annoying, even if not remoted or "housed" - either/both of which are cheap and easy, so even a least-cost open, drip-proof idler is no big deal.

The machine-tools being driven by all this, BTW?

Dead-silent only when switched OFF, are they not?

How far can you really chase "quiet" before an Aviator-style headset with noise-control on its own mic makes more sense.



PS: Acquire your idler motor FIRST. Phase-Craft, for one, recommends slightly different models in their RPC control lineup for 1750 RPM idlers than for 3450 RPM idlers, for example.

PPS: "Slip" is not identical, all motors. RPM may differ slightly one from another and from "synchronous" 3600, 1800, 1200, 900, etc. RPM @ 60 Hz.

Synchronous motors are not a good choice for an RPC idler in any case.

JST said:

RPCs are no more old fashioned than the lathe..... and the darn things are nearly bullet proof. They do not care about voltage spikes, loading, temperatures (within reason) , etc. They pretty much just work. And are repairable, at worst needing another idler motor from the junkyard.

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Well not for 30 years that is!

Heck we just paid off the mortgage on this pile of rubble here. And the converter when in when the loan was new.



Yep, me and ms mulligan own all the walls around that ugly as sin 5 hp idler motor! Yay us.

Is that 3 phase motor connected to the smaller motor (presumably 1 phase) to get the 3 phase motor spinning? (So you don't have to pull start it?)