Digital Phase Converter for lathe

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Bill Shields
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Re: Digital Phase Converter for lathe

Post by Bill Shields »

Disconnect the motor on off push button on the lathe...or move it so that it is very inconvenient to accidentally press.

When the vfd is off the motor will stop. If the power is removed from the vfd the motor will stop.
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John Hasler
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Re: Digital Phase Converter for lathe

Post by John Hasler »

If the guy you bought it from says it's "plug and play" why not take him at his word?
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Bill Shields
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Re: Digital Phase Converter for lathe

Post by Bill Shields »

The old adage"lnow how to tell when a salesman......"

If the instructions say one thing I writing..then Tito make a phone call. One person's definition of p&p is not necessarily universal.
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GlennW
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Re: Digital Phase Converter for lathe

Post by GlennW »

Unless you are running a lathe with a clutch, how would you even reasonably operate it, let alone reverse the spindle direction? Foreword and reverse is usually controlled by two contactors. Kill all power, reverse the spindle direction and then power the entire system back up again? One of the benefits of three phase is instant reversing of the motor...

It seems pretty absurd!

I guess of you have never run a lathe before you would consider that "normal" operation.

I doubt seriously that I could stand to even use a VFD with all of the "ramp up" "ramp down" BS, as I brake the spindle rotation by quickly changing direction of the spindle and do the same for tapping holes.
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BadDog
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Re: Digital Phase Converter for lathe

Post by BadDog »

Agreed. I use so called "plug reverse" (where did that name come from?) far too often to be ok with that.

I did fool with a VFD for 1p->3ph conversion on my mill when I first got it. It was my first 3ph machine. The VFD had provision for a braking resistor, which I intended to use for rapid stop, and for almost immediate reverse. But then I got a 3ph lathe. A lathe can be very problematic to stop/reverse without a massive energy/heat dump. Folks apparently use stove heating elements with some success, but I soon realized that a RPC was a better option, and never looked back. I still have that VFD setting unused for over a decade now. It's going to be placed into service on a belt grinder where it's speed control can be more useful.
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Bill Shields
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Re: Digital Phase Converter for lathe

Post by Bill Shields »

I have a vector drive on my old clunky mill that let's me instant stop and reverse..as you said with a huge heating element.

My clunky belt drive 3 phase lathe won't let me bump stop the chuck so I do not miss it..

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John Hasler
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Re: Digital Phase Converter for lathe

Post by John Hasler »

Bill writes:
> I have a vector drive...

That's the key. Cheap VFDs are V/Hz and cannot deliver the torque that vector drives can.
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liveaboard
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Re: Digital Phase Converter for lathe

Post by liveaboard »

I have 3-phase supply at home; so after adding the VFD (for speed control), the lathe has slow(ish) start and reverse compared to before.
I like it better this way, although it took a little while to get used to it.
I sometimes reversed to brake, but usually let it coast to a stop, so the braking on the VFD saves time.

My VFD doesn't have provision for a heating element, so braking is not so sharp.
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Bill Shields
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Re: Digital Phase Converter for lathe

Post by Bill Shields »

For those of you who do not know...a vector drive motor and control basically has an encoder on the motor so that the control knows the actual speed of the motor (in 50 words or less)
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John Hasler
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Re: Digital Phase Converter for lathe

Post by John Hasler »

There is also sensorless vector control in which the speed and angle are inferred from current and voltage measurements. It cannot match the performance of sensor control but is less expensive and easier to install.
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Bill Shields
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Re: Digital Phase Converter for lathe

Post by Bill Shields »

Ah...but that is not a 50 word or less description....
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pete
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Re: Digital Phase Converter for lathe

Post by pete »

I guess it depends on how the machine is arranged and what additional motors or controls are there for making a decision about a DPC, RPC or VFD. Some of the Euro type mills can have 3 or more 3 ph motors. For my mill with it's single 3 ph motor, it's the standard BP type with back gear and a 4 position step pulley. Using any DPC or RPC would be a huge step backwards. Anything either of those can do the VFD can, plus I have multiple and infinitely adjustable pre programmed speed selections, that ramp up/ramp down that does ease the motor starting loads etc. I've tried visualizing any other method of getting 3 ph out of the standard house hold single ph and there's nothing else that would do everything a VFD can. Between it and the built in mechanical drive on my mill I have anywhere from about 30 rpm to over 4,000. If I had a large shop full of multi hp machine tools, then yes the RPC or a distant second choice would be a DPC would certainly be more cost effective.

It's still not the best or most versatile set up though and I can prove it. At the last mine I worked at we had pretty much unlimited true 3 ph power available. A few million dollars worth every month. Any motor in the mill that was processing the ore and there were hundreds that could benefit from having one had either a PLC or VFD on it. Afaik most of industry today has completely moved to that type of motor control system. Even new industrial level manual machine tools have been available for awhile now with VFD's already built in. And some lathes that can slave the VFD to the DRO for a constant surface speed capability. Newall and a few other DRO manufacturer's make specific models that are designed to do exactly that. It also requires a slightly different VFD that's designed to take those DRO input's so it's not exactly dirt cheap for a home shop and you probably won't find one of those on Amazon. But it's at least worth knowing it can be done.

And I sure don't power the VFD down to switch motor directions. I'm not sure why anyone would. I do have a big fat emergency kill switch up stream from the VFD, but unless I do something real stupid it's used only to power the VFD up or down. For motor direction the mills original 2 spd fwd, rev direction switch is gone and that's what the VFD's keyboard is for. Instant fwd, rev at the touch of a button. But depending on the mill or lathe, then one thing to be aware of that I almost never see mentioned and it almost caught me buying the wrong VFD. If it's got a back gear, then you do need a VFD with that fwd, rev capability and not all of them do. Luckily for me the electrical supplier I was dealing with did ask if my mill had a back gear.
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