3 Phase Motor Advice Needed
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  1. #1
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    Exclamation 3 Phase Motor Advice Needed

    Hi, i'm new to this forum but i've read a lot of threads on here and some of the replies are from really clued up people so I would like to ask for some help.

    I have brought a 3 phase 3 tonne 2 post car lift and would like to know the best way to go about powering it from a single phase input. I have been thinking of a few ways but my knowledge is limited. I have a motor on each lift and the motors are stamped with plates with the following details:

    50hz - delta/star 230v/400v - 3kw - 14.3/8.3a
    60hz - delta/star 275v/480v - 3.6kw - 14/8.1a
    1370/1670 rpm

    So i wanted to know what is the best way to power these 2 motors and from reading i see there are a few pro's/con's and some people having issues with the various methods. The 3 methods below are what I have thought about can someone shed any light on the best route:

    1) A 7.5kw 1 phase in/3 phase out VFD and rewire both the motors to delta and send out 230v 3 phase from the VFD - the only issue is my lift system has a control unit and I have read this can cause issues with the VFD can this be negated by setting up the VFD properly to have a constant voltage out from the VFD or is this an issue?

    2) If the above control unit is an issue can I wire up both of the motors direct to the VFD and then use a forward/reverse switch wired into the VFD? At 50hz and 3kw x2 would the 7.5kw VFD be able to support this?

    3) I have seen a diesel generator it is a Powertech PT6500w with a 3 phase 6500w output however the manual says it has 6500w split equally over the 3 phase and 1 phase outputs. It also only goes up to 380v is this a big issue? Also would i be able to draw 6000w from the 3 phase output alone?

    4) Will a static converter like the clarke pc-60 be able to generate enough power to run the motors. It is rated at 5.5hp

    I am honestly lost on what the best way to go about this is and I have read stories of people buying a VFD and then the motors or VFD tripping out when trying to lift under load. It is a 3 tonne rated post system and I would be lifting about 2.5 tonnes so near max capacity.

    Any help is greatly appreciated. I want to avoid having to buy new motors for it if possible and I want to learn more about using VFD's for 3 phase power.

  2. #2
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    Not really on your list but I used a home-built 5 hp rotary phase converter for several years but finally bit the bullet and got a 30 Hp commercial rotary. The lights blink when I start the converter but phase to phase is within one volt. My feed from the pole is 80 yds of 300 MCM aluminum. Never looked back; however they are spendy.
    I only upgraded to the 30 hp when I acquired a Mazak V5, 11 KVA nameplate. With any power system you want to be conservative and have more power available for starting. If they brown out on startup you'll pop the breakers/fuses on the feed. Worse yet you won't get the job done.
    However, if you can bypass the controller issue then the a vfd with soft start will limit surges.
    Good luck.

  3. #3
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    Similar here...

    Picked up 2 post lift for sing only to notice 3 phase and 3 hp (guessing...)

    Our 1.5 hp RPC would not start it so stored...

    Later in other actions got a 5hp RPC and it works fine.

    Do not consider static.

    Mounted RPC to top of post...needed isolators due to noise.

    Wired outlet to allow additional use for other items.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

  4. #4
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    Get a wiring diagram or draw one yourself.

    Use a VFD to operate the motors

    The control system gets its power from a leg of the three phase, you'll want to separate the control system out from the 3 phase.

  5. #5
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    As stated above the simplest way to get the lift working would be a Rotary phase converter. Plug the RPC into a 220v outlet. Plug the lift into the RPC and you are ready to use your lift.

    I like VFD's and prefer them when ever practical over my RPC but it will take more initial wiring and work to convert your lift to work with VFD's. I would recommend 2 VFD's, one wired directly to each motor. Then use the FWD/REV control on the VFD's to control up and down. A DPDT-CO (Double Pole Double Throw -Center Off) switch should be all you need to control the VFD's. Use one pole for the first VFD and the second pole for the second VFD. ...or plug it into a RPC and be done with it.


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