What motor HP for 3 phase with VFD on 9"?
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  1. #1
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    Default What motor HP for 3 phase with VFD on 9"?

    Looking around, it seems like these lathes either came with a 1/4 or 1/2 hp motor. Would a 3/4 or 1 hp motor on a VFD be too much and damage something?

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    I have a 10K (basically same as a 9) with a .5 hp, and TecoFM50, which works very well and will cause belts to slip before any motor stall. IMO, a 1/4 is small, a 3/4 is overkill but no harm in using one, a 1 is way overkill. The VFD is a very good improvement on those lathes, the 3p motor is much smoother and quiet, no jumping when starting/stopping, much less vibration (and you can tune out resonance with the speed control), infinity variable speed, etc. I bought a brand new baldor 1/2 hp 3p on Ebay for cheap at the time.

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    1/2 HP is plenty for that lathe. I've been running mine with 1/3 HP and VFD for several years now and don't see any indication that it's underpowered. Unless you have the V-Belt drive option, it's going to be belt-slip limited by anything more than 1/2 HP. Higher power won't hurt anything but it's really wasted.

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    Thanks for the input guys. If I go with a 1/2 hp motor, is it worth it to get a VFD that's sized larger than that? Say a VFD sized for a 3/4 HP motor or a 1 HP motor?

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    I’m running a 9A with a KBAC and a 1/2 HP and am very happy with the combination. I have not Been able to stall the motor, but I’m not too mean to it either. It’s a 9A after all.......

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    Quote Originally Posted by Domodude17 View Post
    Thanks for the input guys. If I go with a 1/2 hp motor, is it worth it to get a VFD that's sized larger than that? Say a VFD sized for a 3/4 HP motor or a 1 HP motor?
    There's not any advantage other than if you think you might want to swap the VFD to a bigger motor sometime in the future. The higher hp VFD is somewhat bigger and a little more expensive. Plus its unlikely the 1/2 hp will even be used at its full rating in practice. Cheers

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    Mine has a 3/4hp DC motor w/ variable speed (a slightly different animal than the 3ph). I like the power, but I have stalled it a few times (using a serpentine belt, not leather). When that did happen, the blue chips were flying well! (carbide inserts of course).

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    Just out of curiosity why don't you guys use a Variac to control speed?. Also 1hp 220 volt motors are not that expensive ether. Just wondering?

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    Also what are the advantages of 220v over 110v? I can hook mine up ether way. What would you guys recommend?
    Attached Thumbnails Attached Thumbnails cimg6173.jpg  

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    A variac will not work on a typical syncronous AC motor. The Variable Frequency Drives (VFD) folks are discussing are for 3-phase motors only, and allow speed control, acceleration, deceleration, reversing, and all other sorts of function not required on a basic manual machine tool. And, 3-phase motors are smoother and more efficient, and the VFD allows use of the 3phase motors often found in equipment, without having to replace the motor with an (inferior) single-phase motor. VFD's 1 hp and under are very inexpensive now, around $100.

    Your motor shown above is a single-phase motor, so isn't a candidate for a VFD. Using the 220-volt wiring will halve the required amps versus hooking it up at 110 v. 13.6 amps (at 110v) is a fairly hefty current, seeing that a typical shop/garage circuit will be 15 or 20 amps max, so at 110v it has theoretically taken up about all the capacity of that circuit (granted it's not typically going to draw nearly that much since it's not being used at full load, but the startup current is high also). So for that size motor, if I had a 220v circuit/outlet handy, I'd hook it up to 220 volts, if it was a 3/4 or less hp, it wouldn't be much of an issue for 110v. If a 220 volt outlet/circuit isn't handy, then you can probably use the 110 (assuming there isn't much else on that circuit being used at the same time). Cheers

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    All motors have an optimum speed where their efficiency is greatest. A VFD varies the speed of a 3 phase motor both above and below their most efficient speed. Even though a 1/2 HP motor is plenty for a SB 9, I would choose a 3/4 HP motor with a VFD for that reason. As an example of this practice, An older DoAll 16" band saw with a mechanical variable speed drive used a 1.5 HP motor. The same 16" DoAll band saw made today with a VFD uses a 3 HP motor for the same reason.


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