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Thread: VFD question

  1. Quote Originally Posted by David Kumm View Post
    No Mike, when you run bigger stuff the cost of the power supply doesn't seem so bad. I'm mainly a used guy but have paid 800 for a 15 hp Kay, 1500-2000 for used 10 hp PP, 2500 for 20 hp and 3700 for a 30 hp PP. The PP are worth the upcharge ( I can make you a deal on either a 10 or a 15 hp Kay ). I found I couldn't run vfds off the Kay as the third leg voltage was too wild so any speed control machine needed single phase input. The PP third leg is 208 volts so as long as the vfd can handle that you can run it in conjunction with the PP. Dave
    I see what you mean now
    good to know , I'm in a used buying mode
    Mike >............................................/ Maybe I'm doing this Babysitting Gig to throw off the Authorities \................................................<

  2. #17
    Quote Originally Posted by Tai Fu View Post
    So what exactly is 3 phase? I mean in Taiwan that seems to mean 3 live wires that are 110v each, whereas "single phase" meant 2 of those phases connected together to make 220v. So in the US 3 phase means 3 live wires 220v each? I'm not sure how to get 3 phase but I tried asking around and it's complicated. They said it would cost many thousands of dollars and the power company wouldn't even run 3 phase to your place unless it was a factory. I know many talked about having lots of HP for their tools but being stuck to a 50amp 1 phase circuit means that the biggest motor I could run is a 5hp motor... anything bigger and it's 3 phase.
    I believe the power distribution system in Taiwan is the same as in the US (120V/60Hz). I don't think you're understanding it correctly, though.

    Typical residential power in the US is 2 "hot" legs and a neutral. The hot legs are 120V (RMS, relative to neutral). Because the voltage is alternating (as a sine wave), they are designed to be 180 degrees out-of-phase with each other, and thus, have 240V potential between them. Thus, you connect between a "hot" and neutral to get 120V, and between the two "hots" to get 240V. We call this "single phase".

    For many reasons (including the reason that Mike mentioned earlier), there are benefits to using more than 2 "hot" wires. Typically, commercial and industrial power is "3 phase", meaning there are 3 "hot" legs, each being sine waves 120 degrees apart. Depending on how these are supplied, you can derive 120V, 240V, 208V, and 277V from these (as well as 480V, 600V, and others in some industrial settings).

    3 phase is not typically available for residential service (in the US, at least), for non-trivial reasons. Often, 3-phase transformers are not available in residential areas, making it a much more complicated matter than just "adding a 3rd wire".

    Thus, if you want to power 3 phase machinery, you need a VFD or RPC. I think what is atypical, here, is that your service is only 50A? Most (new construction) residential service in the US is 200A.

  3. #18
    Join Date
    Mar 2013
    Location
    Taipei, Taiwan
    Posts
    537
    My house is old and designed without air conditioning in mind. Modern buildings here are at least 200 amps and 3 wire. The infeed line is 14mm square so I think it can handle 150 amps but I would need to change the main breaker which I don't know how because I can't shut off the meter.

  4. #19
    Join Date
    Mar 2011
    Location
    Rochester, Minn
    Posts
    228
    Quote Originally Posted by Tai Fu View Post
    My house is old and designed without air conditioning in mind. Modern buildings here are at least 200 amps and 3 wire. The infeed line is 14mm square so I think it can handle 150 amps but I would need to change the main breaker which I don't know how because I can't shut off the meter.
    Two things:
    1. I grew up on a farm and we did most of our own wiring, I did all the wiring in my shop and most in my house. Still, I hired an electrician to change the main panel, without hesitation. If it involves pulling a meter, let the pros do it. You want it done right, including the required building permit and electrical inspection.

    2. I am running 3 phase motors off single phase power, through a pair of ABB VFDs that I got off ebay. The 7.5 HP vfd runs a 3 HP motor and the 15 HP runs a 5 HP motor.
    a. To run a 3 phase motor off a VFD with single phase (220 volt) input, the VFD needs oversize capacitors. There are two ways to get this: a VFD that is marketed as one that allows single phase input, or use a VFD that is 2x times bigger than needed.

    b. The motor plate of the 3 HP motor indicates a draw of 8 FLA (full load amps), more of course when it is starting. The power delivery of 8 amps 3 phase = the same as 8* 1.73 = 14 amps from a 2 phase circuit. So I have a 20 amp circuit (12/2 with grd) feeding the VFD. The 5 HP motor's VFD has a larger circuit.

    c. High quality VFDs do a lot of checks: motor speed, current, over and under voltage, .... If you are (un)lucky enough to get one that also checks the input power, then it will not be "hook up and go" with 2 phase input. The VFD will stop and put up an error code, all in the name of helping you out. I don't have wide experience in this area, but my impression is that this is not a common feature.

  5. #20
    I haven't really seen any micro drive accepting 1ph going higher than 3hp. I've used a Hitachi WJ200-022SF in a VT application with a 5hp motor.

  6. #21
    Join Date
    Oct 2006
    Location
    Bloomington, IL
    Posts
    6,009
    Speedstar drives at driveswarehouse has all kinds of single phase 220V AC drives/VFDs above 3hp.

    Hre is a 10hp for example: http://driveswarehouse.com/p-2125-pc1-100.aspx
    Glad its my shop I am responsible for - I only have to make me happy.

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