QT15 Phase Converter Requirements
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  1. #1
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    Default QT15 Phase Converter Requirements

    Hey everyone, I know this is a bit of a contentious subject but having searched a bit it seems there are different opinions floating around about what the true phase converter sizing requirements are for our lathes. I am attempting to find a RPC to run a qt15 which is 15hp continuous or 20hp 30 minute rated. So:

    -Conventional wisdom says double your spindle HP for RPC sizing, does that mean 30hp (2x15) or 40ph (2x20) in this case?

    -The manual recommends some very high amperage requirements (see last post of this thread LINK) Which is probably the right thing to do, but it seems unlikely everyone is actually running 60hp RPCs with 2/0 AWG drops to run their 15hp lathes...

    -Who here is running QT15/20s etc with a RPC, which size did you go with? I see reports of VFD damage when the machine is starved for amperage

    -Some here recommend decreasing accel times (fine by me), how much does this lower the amperage requirements? Enough to allow use of a smaller RPC?

    -I will never fully load this lathe, but on the off chance it happens by accident I don't want to fry anything. Does anyone know if this is likely to happen if I have a converter sized to normal use but it suddenly overdraws under an extreme load?

    Thank you all for any experience / information you can share on this subject.

  2. #2
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    I have been running my QT10 off 40hp(2x20hp) for a couple years now. No problems at all but i limit rpms to 3000. Before that ran it off 20hp with the accel times turned down and i would limit max rpm to 2000rpm. Also never really loaded the spindle but when i did the control would alarm out with an "under volt alarm" which i"m sure wasn"t very good for my machine. That is why i added the 2nd 20hp motor to my converter. haven"t had a hiccup since.

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    Castleville - your QT10 has the 10hp spindle (15hp momentary) correct?

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    I have a QT15 running on an American Rotary 30hp converter. Works fine. I also run other smaller machines off the same rpc at the same time. I have yet to try running my Brother at the same time but will at some point.

    I do believe if you do everything by the book you would come up with a bigger RPC. In the interest of treating my geriatric Mazak nicely I have reduced the max rapid speeds and reduced the acceleration of my spindle. I think this helps with power load too.

    This setup has worked very well for me.

  5. #5
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    john yes that is correct.


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