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Thread: VFD vs Staticv Phase converter

  1. #1

    VFD vs Staticv Phase converter

    I just bought my son a used cabinet saw that has a 3hp 3 phase motor. My own cabinet saw also has a 3 phase motor and I have used a rotary phase converter for the past 15 years. At any rate I need a phase converter for his saw and was wondering about using a VFD. I know how a phase converter works(both static and rotary) but am unsure of the VFD. Does anyone use one for a table saw and can you reccomend a brand and how to determine the size needed.

    Thanks


    Fred,

  2. #2
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    I use one for my wife's lathe, and my bandsaw mill.

    You'll need one that will run a 3HP motor with a single phase input.

    I happen to have a Baldor Industrial VFD, you can obtain other brands in the US for very little money............Rod.

  3. #3
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    I've had 4 VFD's so far, and need to order another for my Unisaw I just bought. They're simple to setup, small, and offer functions a RPC doesn't. Some functions like variable speed don't mean much on a TS, but you can have motor braking and soft start which is nice.

    I'd recommend getting a TECO FM-50 from Factoration.

  4. #4
    Teco makes a good VFD - you'd want something like this for a 3HP motor:
    http://www.factorymation.com/FM50-203-C

    There are also lots of "no name" ones available, such as this one on ebay. Most of these are all using the same IC and "transistor pack" (sourced from reputable manufacturers) and just adding their own user interfaces, enclosures, etc, so they aren't as "risky" as you might believe a no-name offshore-built piece of complicated electronics might be

    As Matt says, a VFD is really nice. You can add a braking resistor to make the saw blade stop almost instantly (although you'd need to make sure it doesn't unscrew the arbor nut, in the process). There's no power consumption and no noise when idling (unlike an RPC). For a table saw, the speed control is probably not useful, but if you wanted to mount something like a sanding disk, that might be handy.

    Nothing tricky about choosing one, either: you just need to pick one that supports a 3HP output on a single-phase input (which will certainly require 240V).

  5. #5
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    I had one of the 3hp eBay specials for $116 IIRC. My main complaint was the "instructions" were pitiful and it took many back and forth emails with the "support team" to get it working properly.

    TECO's (~$200) are great for ease of setup and customer support.

  6. #6
    I have a one VFD on a Clausing Drill Press and I love it because I can slow it down or speed it up. Last weekend my home built 7.5 HP Rotary Phase converter blew its idler motor. I purchased a new 10 HP unit from American Rotary. My largest motor is on my 5 HP Tannewitz table saw. The thing about a VFD is if you have a magnetic starter on your machine you will have to bi-pass it. Also you could use multiple machines on one VFD, but it gets wiring hairy. If you were going to have multiple three phase machines I would recommend the Rotary Phase Converter route. My old one served me well for 12 years, it was most likely just a bit underpowered for the Tanny. A rule of thumb for both VFD's and Rotary Phase coverters, you need to double the horsepower you are serving. For instance if you have a three horse power table saw, you will most likely need a 7.5 HP VFD to properly run it. If you have a 5 HP table saw like me, you will need a 10 HP Rotary Phase Converter to properly run it. You most likely know this since your already run a table saw off a RCP. I'd shy away from a Static, I think these just start the three phase motor so it can run on single phase providing only about 50-66% the horsepower of the motor.

    Hope this helps.

  7. #7
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    Quote Originally Posted by Eric Commarato View Post
    I have a one VFD on a Clausing Drill Press and I love it because I can slow it down or speed it up. Last weekend my home built 7.5 HP Rotary Phase converter blew its idler motor. I purchased a new 10 HP unit from American Rotary. My largest motor is on my 5 HP Tannewitz table saw. The thing about a VFD is if you have a magnetic starter on your machine you will have to bi-pass it. Also you could use multiple machines on one VFD, but it gets wiring hairy. If you were going to have multiple three phase machines I would recommend the Rotary Phase Converter route. My old one served me well for 12 years, it was most likely just a bit underpowered for the Tanny. A rule of thumb for both VFD's and Rotary Phase coverters, you need to double the horsepower you are serving. For instance if you have a three horse power table saw, you will most likely need a 7.5 HP VFD to properly run it. If you have a 5 HP table saw like me, you will need a 10 HP Rotary Phase Converter to properly run it. You most likely know this since your already run a table saw off a RCP. I'd shy away from a Static, I think these just start the three phase motor so it can run on single phase providing only about 50-66% the horsepower of the motor.

    Hope this helps.
    That's not true for VFD's, at least up to 3HP. If you have a 3HP motor, get a 3hp VFD.

  8. #8
    Quote Originally Posted by Matt Day View Post
    That's not true for VFD's, at least up to 3HP. If you have a 3HP motor, get a 3hp VFD.
    +1. You don't need to oversize the VFD. Size it for the motor it is driving.

    And, yes, the instructions for the ~$100 eBay VFDs are....lacking. But it's not terrible - certainly it can be figured out with some time and trial-and-error.

  9. #9
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    For smaller items, a TECO/Westinghouse works just fine. My friend, Bruce Norton, who does a LOT of things with VFD's will tell you that most are good but the more costly ones have a better sine wave (he's an engineer). He says for motors, the sine wave difference won't justify the difference in price on the best models because motors are far more forgiving than electronics. We had this conversation last night on the phone. He recommended considering the Hitachi VFD or the 7300 series of TECO/Westinghouse. While visiting Bruce in Tennessee on Sunday, I took a couple photos of a FEW of his tools on VFD's.

    Bruce.jpg

  10. #10
    " certainly it can be figured out with some time and trial-and-error."
    LOL. 'Im always a bit concerned about trial and error with electrical stuff cause once you let the smoke out its REALLY hard to put it back.

  11. #11
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    Quote Originally Posted by fRED mCnEILL View Post
    'Im always a bit concerned about trial and error with electrical stuff
    That's exactly why I think you should get a TECO FM-50. Excellent directions (I suggest you print them out full size, as a little booklet is supplied with the drive, see below), and excellent CS from Factorymation if you need it.

    http://manuals.chudov.com/TECO-FM50-Manual.pdf
    Last edited by Matt Day; 01-06-2017 at 2:04 PM.

  12. #12
    The nice thing is that most VFDs are very forgiving, in the sense that they have built-in protection for over-voltage, over-current, over-speed, etc. So there is low risk of blowing anything up. But they can also be onerous to set up, since they allow you to adjust all those protection settings (and a seemingly infinite number of other things), often through a rather overwhelming menu of parameters (eg - "Use the up/down arrows to navigate to parameter #b01-45, press the 'Enter' key, then use the up/down arrows to adjust the value of maximum motor speed, expressed in 'RPM divided by 10', or expressed in 'RPM divided by 100' if parameter #b02-34 is set to '1'")

    I agree with Matt, though - the TECO is a much more user-friendly first VFD...

  13. #13
    I'm just re-stating what a VFD salesman said to me...maybe he was trying to sell me a more expensive VFD...


    Quote Originally Posted by Dan Friedrichs View Post
    +1. You don't need to oversize the VFD. Size it for the motor it is driving.

    And, yes, the instructions for the ~$100 eBay VFDs are....lacking. But it's not terrible - certainly it can be figured out with some time and trial-and-error.

  14. #14
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    I have a teco fm-50 on my drill press, very easy to set up and works great. I would recommend this route as well.

  15. Sizing a VFD for phase conversion boils down to current (amps). When going from a single phase input to three phase out put you will need the drive to be capable of putting out 1.73 times the motor nameplate amps. You roughly de-rate the drive by half. I work in the electrical field and we routinely put VFDs on three phase irrigation motors where only single phase power is available. They do not work unless properly de-rated. I suppose one exception would be a motor that isn't under a load and therefore not pulling anywhere close to its nameplate amps. Once a load is applied the drive would likely trip/fault if not sized correctly.

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