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  • uncle pete
    replied
    My electrical skills and understanding could fit on the head of a very small pin, But after seeing what a 3 phase motor VFD combination can do on my mill I'd never go back to single phase. Smoothness of opereration, Soft start, Programable ramp up/down, Variable speeds ect. In fact I plan to change my single phase lathe motor over to a 3 phase VFD set up. Forrest's point about not getting too far away from the motors normal operating range is of course 100% correct. Everyones needs and wants are different, But for 99% of us here I think that a VFD is the way to go.

    Pete

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  • lakeside53
    replied
    Originally posted by MichaelP
    You'll need a separate one for each machine. Sorry!

    Lakeside53,

    Thank you for the very interesting link.

    Now, some measurements and calculations demonstrate that my 3-phase RPC-based line, when fully unloaded, is 3.4% unbalanced. This is only slightly above the recommended 3% max. for the utility lines, but well below the 5% max. permitted by Nema MG-1 for motors.

    As soon as I turn on one of my machines, the unbalance drops to 1.8-2%. Based on the table presented in the article, I can derate my motor to about 95-97% of its full capacity to be very safe. And it's not because the motor loses power, but in order to keep it at specs at full power (in terms of heat). Anything to avoid an extra 10% of temperature rise if I decide to take the motor to its limit.

    How often, if ever, we operate our motors at their full capacity is, really, a rhetorical question.

    You are one of the lucky owners then; good, you can sleep at night You can even run cnc from that. Most rpcs I measure are far from balanced, and the owners are safely oblivious. In addition, most equipment I see in the home ship doesn't have over current protection for the motors, so I guess that they don't know won't hurt them Must be true, because few homeshops actually burn out motors.
    Last edited by lakeside53; 08-21-2011, 10:27 PM.

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  • lakeside53
    replied
    Originally posted by PixMan
    What do you mean by this?

    A Phase Perfect Digital Phase Converter is no laughing matter in price or performance. Full power, perfectly balanced phase and voltage, and dead quiet. They are anything but cheap but if you're trying to power-up a 1990's vintage CNC mill or lathe such as I anticipate doing, a Phase Perfect DPC is the closest thing to incoming 3-phase, and probably cleaner.

    http://www.phaseperfect.com/

    Do you mean you have purchased and installed one of their products? If you have one of these, why spend even more money on 3-phase VFD's? I can see where some speed control on some machines would be nice, but it sounds like you'll be spending beaucoup bucks on power supply stuff. I try to spend it on tooling and machines.


    yes, I just purchased and installed one (blue box to the left). 10hp unit for $1500 from CL - about half price. It currently runs my lathe and compressor, and a few extra outlets for whatever.






    VFD's offer much more than three phase conversion. Soft start, rated motor starter (over current protection) etc etc. and... single phase vfds over 3 hp get expensive. 3 phase means I can buy cheap surplus vfds. Industry seldom buys used vfds; homeshops rarely have 3 phase


    I'm about to intall a 240->480- transformer to take advantage of even cheaper vfd's
    Last edited by lakeside53; 08-21-2011, 10:26 PM.

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  • flylo
    replied
    If you change motors I'd like to buy your 3 phase. Please let me know as soon as you decide. Thanks! Eric

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  • Forrest Addy
    replied
    Well, IDEALLY you need a VFD for each three phase motor (single phase motors cannot be made to work from a VFD).

    BUT - I went for years swapping plugs on my lathe and mill on a single VFD. I set the VFD in a central location, added a drag around control station with a magnet mounted on the bottom, made a long cord from control station to the VFD, and used good three phase rated plugs on the power connectios. I used this set-up from 1993 to 1998 when I lucked on to more VFD's.

    A lot of home shop owners mounted their VFD's on a little stand they took from machine to machine. A VFD may run only one motor but it will run any three phase motor in a range from a little larger to 1/3 its rating - depending on the motor and how the VFD responds to it. You may have to jigger the parameters if the motor range is too extreme but that takes seconds once you're practice. Post a how-to cheat sheet on the VFD.

    In the mid '90's, my VFD was a MagneTek GPD333. My mill motor is still 2 HP and Chinese. The lathe motor at the time was 5 HP and German. No parameter changes required. YMMV
    Last edited by Forrest Addy; 08-21-2011, 05:55 PM.

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  • davidwdyer
    replied
    Originally posted by MichaelP
    You'll need a separate one for each machine. Sorry!
    Well, that settles that question for me anyway. Everything is already working great without one.

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  • MichaelP
    replied
    You'll need a separate one for each machine. Sorry!

    Lakeside53,

    Thank you for the very interesting link.

    Now, some measurements and calculations demonstrate that my 3-phase RPC-based line, when fully unloaded, is 3.4% unbalanced. This is only slightly above the recommended 3% max. for the utility lines, but well below the 5% max. permitted by Nema MG-1 for motors.

    As soon as I turn on one of my machines, the unbalance drops to 1.8-2%. Based on the table presented in the article, I can derate my motor to about 95-97% of its full capacity to be very safe. And it's not because the motor loses power, but in order to keep it at specs at full power (in terms of heat). Anything to avoid an extra 10% of temperature rise if I decide to take the motor to its limit.

    How often, if ever, we operate our motors at their full capacity is, really, a rhetorical question.
    Last edited by MichaelP; 08-21-2011, 06:56 PM.

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  • davidwdyer
    replied
    As you can see, I don't have a VFD, but it sounds like someone would need a different one for every machine. Is this the case or can I use one for the whole shop but only use one machine at a time?

    Sorry if this is a dumb question, but I never have worked with VDF before.

    Leave a comment:


  • Forrest Addy
    replied
    I'm often challenged when I assert the 85% figure on HP attainable on motors run from an RPC. It's more a figure of merit than quantifiable expectation. 85% is pretty close to 100%. Without instrumentaton I doubt if I could tell if a machine motor was giving 100% or 85%. Most induction motors will 15% overload for the two or five minute duration of a cut. The motor will hum a little louder and the induction motor slip might be noticable in the note from the gear meshes. Otherwise I'd think the motor under 15% overload would do little other than warm a trifle more than normal. Keep it up for an hour and you may fry the motor. Depends on ambient temperature..

    It stands to reason that an RPC balanced to run equal voltages at idle current will still have a weak leg at full current demand from the load motor. Whether the difference is 90% or 80% much depends on the relative rating of the idler motor, the load motor, and the circuit elements that "balance" the weak leg.

    You really can't make these distinctions without instrumenting each individual case. Once upon a time I had time and resources to do just this. Results varied so I picked 85% as a fair approximation and went with it. YMMV

    A VFD is not a universal solution. A little experience and strategy is needed to take full advantage of its benefits and features. A plain one motor manual machine benefits out of proportion to the investment from a VFD.

    If you have single phase power and a complex machine combining motors, digital controls, and other wierdness, a Phase Perfect is the way to go. The output of a Phase Perfect can be treated just like three phase from the utilty company. Your machine won't know the difference except the power is a little cleaner on the synthetic leg.

    Rant mode: The witless will install a VFD on a mill, set the step pully at 1700 RPM, dial the spindle speed down to 450, stall the mill with a 4" carbide shell mill, and forever after condemn a VFD as "having no torque". Idiot assertion.

    People shouldn't use big words like "torque" if they don't understand what they mean. Torque is twisting force not power. You wouldn't lever up a rock by placing the fulcrum near your hands because of the mechanical disadvange. Similarly, you don't belt or gear a machine for high RPM, dial it down and expect it to develop full rated motor power at low RPM. An induction motor is a constant torque device. Dial it down in RPM and the developed mechanical power drops in proportion.

    In these situations it's the operator setting conditions that's at fault not the VFD "reducing torque".

    When ignorance of physics doesn't kill, it humiliates you or costs you money.

    OK, rant off. The topic was a Bridgeport with a three phase motor. Yes, a VFD will do the job of running its three phase motor from single phase power and the features incorporated in a VFD will greatly enhance the operabiliy and performance of the machine. Thousands have made the conversion on similar amachines but very few were dissatisfied.
    Last edited by Forrest Addy; 08-21-2011, 05:38 PM.

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  • davidwdyer
    replied
    Originally posted by jcon
    mich 88 13

    I do not understand what davidwdyer means by an idler motor. I ran my old 3 phase motor by hooking a capacitor to the third lag of the motor with a button hooked to one wire of the singer single phase. Turn the switch on while holding the button for a few seconds, the motor will run fine, but with some loss of power. Do not hold the button after the motor starts.

    Jcon (Jim Connell)

    You haven’t began to learn till you learn how little you know
    The idler motor is used as you are using the normal motor with a capacitor to start it. Except that the idler motor, while idling, generates your third leg of three phase although it does not generate 100%. This is a cheap way two produce "3 phase" with only slight reduction of power. I've never noticed any lack of power. However, using an "air over" motor is slightly noisy.

    Your motor, when running was only running on two legs, which must have noticeably reduced power. Perhaps unbeknownst to you, it was also generating a third phase of power which went unused.

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  • jcon
    replied
    Bridgeport Motor

    mich 88 13

    Sometime in the 70’s I bought a G.E. single phase ¾ Hp 115/ 230 motor from the local Bridgeport Dealer. It bolted on to my Bridgeport with no changes needed. It reversed instantly just as will as a three phase motor.

    I do not understand what davidwdyer means by an idler motor. I ran my old 3 phase motor by hooking a capacitor to the third lag of the motor with a button hooked to one wire of the singer single phase. Turn the switch on while holding the button for a few seconds, the motor will run fine, but with some loss of power. Do not hold the button after the motor starts.

    The ¾ Hp motor or the loss of power with the 3 phase motor has never been a problem .

    Jcon (Jim Connell)

    You haven’t began to learn till you learn how little you know

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  • JoeLee
    replied
    Originally posted by macona
    Install a VFD.
    Agreed, this is your best bet. Yaskawa makes some real nice VFD that will run that mill without a problem.

    JL.................

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  • PixMan
    replied
    Originally posted by lakeside53
    Phase Perfect? ha, I just put one of those it, so now I'll run three phase vfds as well.
    What do you mean by this?

    A Phase Perfect Digital Phase Converter is no laughing matter in price or performance. Full power, perfectly balanced phase and voltage, and dead quiet. They are anything but cheap but if you're trying to power-up a 1990's vintage CNC mill or lathe such as I anticipate doing, a Phase Perfect DPC is the closest thing to incoming 3-phase, and probably cleaner.

    http://www.phaseperfect.com/

    Do you mean you have purchased and installed one of their products? If you have one of these, why spend even more money on 3-phase VFD's? I can see where some speed control on some machines would be nice, but it sounds like you'll be spending beaucoup bucks on power supply stuff. I try to spend it on tooling and machines.

    Leave a comment:


  • lakeside53
    replied
    Originally posted by MichaelP
    Where did you get the number, Forrest? It looks like it belongs to a good static converter rather than to a reasonably well balanced RPC.

    All sources I ever seen quote full power when a motor is run out off a well balanced RPC. Granted that the output of an RPC is not as ideal as a 3-phase utility power, I doubt that you'll ever notice the difference in terms of your machine power.

    Balance? at what load? How many RPC are realy balanced within 5% at max load? How can the average guy at home even do this?

    Still, you may be able to get 100% out, but at the expense of your motor. Motor are supposed to be derated if the voltages are unbalanced. A 5% unbalance requires derating to 75% or so... here a useful link to explain:
    http://www.pge.com/includes/docs/pdf...lance_rev2.pdf


    Static converters? I will never use one on any motor I care about. Maybe you get 50% power before you are overloading the motor, and how do you know? If you 'hear" it slow down, it's already way into overload.
    Last edited by lakeside53; 08-21-2011, 12:18 PM.

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  • lakeside53
    replied
    Originally posted by PixMan
    How does a VFD work with the step-on-it brake of our lathe or the little brake lever on the Bridgeport that I've instinctively reached for over the last 35 years? Does one need an EE to wire the VFD into the circuits of the lathe's Forward-Neutral-Reverse lever, brake and jog buttons?
    ......

    I could be convinced to go VFD in the future, but I'm more inclined to look at a Phase Perfect as I intend to someday install CNC milling and turning machines.

    You can't use the brake on the vfd if you have programmed deceleration; simply set the vfd to freewheel on deceleration (i.e., it just cuts the power). On your mill, just take the handle off the brake On some VFD you can feed the the lathe brake switch to the vfd and have it freewheel only when you stomp on it.

    Phase Perfect? ha, I just put one of those it, so now I'll run three phase vfds as well.

    Leave a comment:

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