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Thread: Drill press table?

  1. #11
    Supporting Member high-side's Avatar
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    You can run that 3-phase motor from single-phase residential power. You will need to use either a phase converter, or a Variable Frequency Drive. I have a VFD running a 3-phase motor on one of my CNC Mills.
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  2. #12
    Masterjuggler's Avatar
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    I admit, I did dismiss the idea of using that motor relatively quickly, so I did some more reading on it and looked into various options.

    VFDs are ideal (relatively for my situation), but they're pretty expensive for a home shop, or at least more than what I'd like to spend to get this motor running well. Especially to get one with a voltage doubler circuit to get from 115V to 208/230V (motor handles 208-230/460, with high/low configs), it'd run me at least $300 for something that won't break down tomorrow. For that kind of money, I'd rather just buy a new single phase 1.5hp motor, or better yet, haul a craigslist treadmill over in a u-haul (no friends with pickups) for its motor.

    There are two other cheaper options, the first of which is to make a rotary converter. I don't have access to another three phase motor to be the pony, and that sort of elaborate setup is overkill for my situation. I could see it being a lot more useful in a shop with many three phase tools and only single phase power.

    The second option is to use a Steinmetz Circuit, which is essentially just using a capacitor to change the phase of one coil enough to make it technically three phase. There are a lot of issues with this, mainly that the capacity only changes the phase by 90* (theoretically, in reality less than that) so you have a crazy elliptical magnetic field going on. What this means during use is maximum hp is reduced to 70%. You also get voltage spikes in the upper 300's and very low starting torque. I might actually do this because even at 1.4hp (70% still far better than my small single phase motors). Because start torque is reduced to like 30% of normal, I might need to include a start capacitor, either manually activated or some sort of automatic switch.

    With any of these, I would need to step up my 115V to ~230V (either through a $50 converter or more likely a rewound microwave transformer or two).

    Well, after all that thinking, in the end it still probably makes more sense to use that 2hp motor in a less-than-ideal configuration than my smaller single phase motors. I happen to have the right capacitors on hand, now I just have to find yet another microwave transformer. I can't seem to get enough of those things.
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  3. #13
    Masterjuggler's Avatar
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    Just wanted to post a bit of an update on what I ended up doing. After trying to use capacitor setups with run and start caps, it was a big pain and I would have had to spend some money on proper caps anyway, so I got a Chinese $100 VFD. Definitely money well spent, works far better than I ever thought it would. Proper frequency control and reverse functions, no start capacitor timing to deal with, and no loss of torque from run caps.

    I did get a microwave transformer and just rewound the secondary to output 220v. I can get about 45min of good grinding in before I worry it gets too hot. Probably just a simple 120v fan would fix that.

    I think the most likely use I'll get out of the drill press is turning it into a small lathe or tool grinder. Something where I might be able to re purpose the spindle too. For now it's still acting as my drill press, but I plan to upgrade to an older used one eventually.


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