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Thread: VFD for 7.5 hp 3 phase to run on 220 single phase

  1. #1

    VFD for 7.5 hp 3 phase to run on 220 single phase

    Anyone with any experience running a 7.5 hp 220 volt 26 amp 3 phase from a VFD powered by 220 single phase? I would like to know
    a) what specific vfd you are using if you recommend it,
    b) any issues I should be aware of

    The motor is driving a 1995 Lazzari Tema 3000i. The alternative for me is to swap out the nice italian motors for single phase 5 hp main and 1 hp scoring. I doubt I will strain a 5 hp motor, as the Unisaw this is replacing only had a 3 hp and I never made it work to hard. The Lazzari uses either 10 or 12 inch blades, and I imagine the 12 inch blades might take a little more power, but comments from users with 5 hp 12 inch machines would be appreciated also.

    Thanks in advance.

    Picked up the saw in Detroit over the weekend and have it complete disassembled for cleaning and rebuild. Looked like a basket case when I got it but think it will clean up nicely. Built like a tank.

    Mike

  2. #2
    You will need a separate vfd for the scoring motor. Also, since you can't have any switching between vfds and motors the original controls will be bypassed. If you want to use the existing e-stops they will have to be rewired to cut power to the vfds. Alternatively you can set up remote start/stop stations.

    I run a Paoloni P260 saw with12" blades and (approx.) 6 hp motor from a rotary phase converter. It works well since I don't need speed control and I can run other 3 phase machines off it.

    I think you could run your saw on a 5hp 1ph main without a problem but the new motors won't be inexpensive and it may be difficult to find a single phase scoring motor that fits. Also, you will have to reconfigure the controls to single phase.

    If you are looking for the least expensive solution consider a static phase converter. You will get only about 2/3 of rated power. I have run a slot mortiser (admittedly grossly overpowered at 3hp) on a static converter for 30 years.

  3. #3
    There is an excellent thread in the Workshop forum on options for powering a 3-phase slider: https://sawmillcreek.org/showthread....ase-convertors

  4. #4
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    Start by looking at prices. A VFD for a motor that size is really expensive. I went with a rotary phase convertor and wired in a 3 phase breaker panel in the shop for other 3 phase machines.

  5. #5
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    Since you have 2 motors and a big main motor, Iíd suggest a rotary phase converter. For a 7.5hp motor youíll want a minimum of a 10hp idler, if not 15.

  6. #6
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    If you go VFDs, contact Automation Direct. They will set you up with the correct VFD for each of your motors. However, a VFD for a 7.5hp motor is probably pushing $600, and then the scoring motor will need another $200+/- VFD. At $800, you might be better off with another means of conversion.

    Unless you are powerfeeding stock, or ripping 12/4 hardwood, i dont think you will ever be disappointed with 7.5hp on a 12" blade.

  7. #7
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    I have been looking at something similar albeit a belt sander. (in the workshops threads).

    Once you go over 10hp on the VFD the choices drop, and what I have read recommends 2x VFD rating over the machine. So 7.5hp would ideally mean a 15hp VFD. Price goes up. Then you have the second VFD for your smaller motor.

    For a rotary phase convertor (what I have now, a 10hp Phoenix), to get it 'properly' wired means something like what Richard writes with 3 phase breakers after the convertor in addition to a fairly large input breaker. A decent size RPC in my area can be had for around $500 used. But install is more than this (wire, panels, breakers, etc) I think I would not purchase a VFD used, and some warn against the chinese versions (which may be cheaper)

    Having said that I do have a 12" blade on my smart 300 and it has never bogged (4hp perhaps), so I cant imagine you would over tax the saw by derating a bit (keep the blade sharp). Just my opinion there may be users here that do push it to the limit.

    Swapping motors is not crazy. Then you can always plug it in like any other equipment. But if you think you will collect more 3 phase equipment then permanently wiring in a RPC with breakers may be a good route.
    Last edited by Carl Beckett; 03-22-2022 at 2:36 PM.

  8. #8
    Thanks for all the responses.

    Current single phase equipment includes a 350 mm Minimax J/P, Aggazani 5hp 600 mm bandsaw, and a Hammer sliding table shaper. 3 hp cyclone dc.

    I will try to get VFD's to work to keep the saws original motors intact, but if the vfd for the main is not feasible, will replace the main with a 5 hp 1 phase, and get a vfd for the little 4 amp 3 phase scoring motor. Again, everything else is single phase, so want to keep it simple if possible.

  9. #9
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    Buy a 5 hp VFD with single phase input and program it to limit the output to 5 HP.

    Youíre never going to use even 5 HP.

    Add another small VFD for the scoring motor

    Iíve modified a few saws that way, works greatÖ.Regards, Rod.

  10. #10
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    Why arenít you considering a RPC? Itís the best way to keep it original (change nothing) and have full power.

  11. #11
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    I have several 7.5 hp motors I run them each with there own vfd. I have had good luck with the fuji brand they make vfds that are designed to support single phase input. I believe this is the model of the ones I have FRN007G1S-2U. I got mine from Marshall wolf automation.

  12. #12
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    I have been running my 7.5hp RedStar radial arm saw on a Fujitsu VFD of proper rating for near a decade now. I have never had a problem.

    I ran it for several decades on a home built RPC before that... I REALLY don't miss the hum of the idler motor on the RPC!

    How comfortable are you with wiring? A big VFD and a second small VFD for the scoring blade with those nice Italian made motors would be awfully nice and probably a lot cheaper than new motors... but only if you are comfortable digging to the wiring on the saw.
    Last edited by Michael Schuch; 03-23-2022 at 11:04 PM.

  13. #13
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    Check if the saw has a break on the main motor and if it does make sure you tell the company selling you the VFD. It may or may not be an issue.

  14. #14
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    Quote Originally Posted by Rick Fisher View Post
    Check if the saw has a break on the main motor and if it does make sure you tell the company selling you the VFD. It may or may not be an issue.
    Friction brake motors on euro machines are a pain with a vfd. The solution is to disengage them or don't use a vdf.

  15. #15
    Thanks for all the input. Will look at the FUJI vfd's. I am not too concerned about doing the wiring - but have a friend who is an electrician if I stumble, or to look things over before I push go. I don't think the motor has an integral brake - we took it to a friend who has three phase to test it and it kept spinning after power was turned off. I assume that would mean there isn't one or it's broken.

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