Static Phase Converter?

d.com says...


I was able to keep all the original functions of the 2- speed motor on my lathe when I installed a VFD. The two speed select contactors are between the VFD and the motor windings, and work as they always have. The direction commands to the VFD come from the reversing contactor, which no longer has any direct connection to the motor.
The only thing I can't do (you *can*, but for the reason you mentioned, *shouldn't*) is switch from hi to lo on the fly, but that's not a problem now that speed is controllable with the VFD's speed pot. Most VFDs have a zero speed output, so it would be possible to prevent switching the speed select contactors unless the motor is stopped, but I didn't think it worth the trouble.
Ned Simmons
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    [ ... ]

    O.K. The switching between the VFD and the motor is what most VFD manufacturers explicitly warn against.

    That depends. If you are the only one who ever uses the lathe, you can probably depend on remembering the proper operation. However, with multiple people using the same machine, with a constant potential for a new hire to not have it locked into his memory yet, I would think that such an interlock would be well advised.
    Enjoy,         DoN.
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On 13 Oct 2005 06:24:06 GMT, snipped-for-privacy@d-and-d.com (DoN. Nichols) wrote:

Rather than risk frying the old two speed motor on my TM mill, I got a 1 hp. Marathon inverter duty motor to go with the VFD. Good motors aren't that expensive, or find a used one. The VFD handles generating the low speed end well.
Pete Keillor
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    [ ... ]

    [ ... ]

    O.K. This is a reasonable approach, as long as the motor is not mechanically unusual in its mounting, thus making the finding of a replacement more difficult.
    Enjoy,         DoN.
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On 13 Oct 2005 06:24:06 GMT, snipped-for-privacy@d-and-d.com (DoN. Nichols) wrote:

Absoutly correct Don. Bad things MAY happen when switching the lathe controls when operating via a VFD.
I pulled all my lathes off the several VFDs and run them all on a 5hp RPC for this reason.
The sole exception is that 9-18 Rivett that I wound up with several months ago. It has a two speed motor..but last weekend, for the first time I pulled the tarps and shrink wrap off of it..and discovered the damned thing is 480vts....(Im not happy camper with a certain Vietnamese charector because of this)
I could stick in one of the very very expensive 2 speed Hardnge motors I have on hand...but I can sell them for more than the lathe is worth..so will likely put in a single speed 3ph motor and run it off a VFD. Its only a second ops lathe..so its no big deal.
Gunner
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wrote:

I'm not sure I understand exactly how bad things might happen with a VFD. Do you mean switching something like a dual-speed motor or some other electrical control while it is being driven?
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wrote:

Correct. If for example..I were to use the onboard reversing switch...it momentarily interupts the power from the vfd..then spikes it badly when it makes up again. Some serious spikes.
Think of it as spiking the clutch on your vehicle..while doing "hole shots".
Sooner or later something will bust. With luck..it will simply be a universal joint..but it could be the differential or tranny.
Gunner
"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner
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wrote:

Yep. Did that. Or torquing against the brakes on an automatic. Never broke anything like that I can remember. Other ways... other stories... mostly dumber.

Gotcha. Thanks.
Uhhhmm... but an RPC is better for not causing problems when you power switch? Just thinking out loud. But I'm not worried yet.
After posting a couple weeks back about slowing my lathe, I ordered a Hitachi VFD and found a motor, cheap and local. Amazing what a handful of electronics can do these days. I had to read the book for a few days to begin to understand what to think about setting and how I might want to interface to it. Incredible configuration options in the VFD.
Need to go buy some wire this morning to hook up the motor, then I'll try it on the ground for a while. I plan to bypass most of the existing lathe electrics, so I think it will all be good and I should have new things like jog too.
I'll probably resurrect the other thread after I get things going, or if I find some uglies.
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wrote:

Yes..because an RPC doesnt use delicate electronics. It uses the brute force method.

Use the existing lathe Switchs to operate the VFD. Virtually everything is there already, though in some cases..if for example your forward/reverse switch was a momentary and picked a relay..you may have to replace it with a maintained version, though some VFDs have momentary input options. They are actually an amazing contraption <G> and the designers have gone to great lengths to make them as usable as possible under just about any configuration you can imagine. Well..the good ones anyways <G>. From machine tools to pumps, air handling and motion control. And Neptune washing machines......
Gunner
"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner
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wrote:

Yeah. The thing that really amazed me reading the manual is the capability for PID feedback control in various kinds of ways. I don't plan to use that, but I never expected it to be there.

My current plan is to remove the existing control panel and replace it with one of my own design. Existing panel has three identical sized buttons for Fwd Stop and Rev. I'd like to find a big red button in case I ever need to panic-stop the thing. Had one scary screw-up already.
Also plan to remote the speed knob and add a control for jog. This VFD allows lots of remote functions through low-voltage wiring. Seems like it shouldn't be very hard to set up.
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You can build a 10 HP rotary phase converter for next to nothing, in a couple of days, see how I did it
http://igor.chudov.com/projects/Phase-Converter/
I am using it very often these days. Works fine, unless it is overloaded, in which case it is merely mediocre.
With a static phase converter, you will not be able to realize the full nameplate power of the motor, may have problems reversing it, and it would run in an unbalanced mode.
Static phase converter is not really a phase converter, it is a starting circuit that spins up 3 phase motors and lets them run on single phase once they spin up.
i

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JB wrote:

I run a 5 horse 2 speed as you are speaking of on a 7.5 horse rotary built from a phase-a-matic heavy duty static converter rated for 8 hp. It will NOT start the lathe on the low range but doesn't have any problems at all with the high range.
Yea, I know...I need bigger. I just wanted to throw out some numbers that may help. I would suspect that you will not get good service from a static converter alone. It may be "good enough" for light work in the speedier gear range but you'll have to seriously oversize it to go into the low range.
Koz
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