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Thread: Soft-start motor switch

  1. #1
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    Soft-start motor switch

    Can someone recommend an appropriate soft-start switch to use with a 3-phase 5 hp 1750 rpm motor?

    It's going on a band saw, if that matters.

    Thanks, Mark

    I don't know why the two sideways photos of the nameplate are below the post. I also cannot remove them. Sorry for the duplication.

    motor nameplate.jpg
    Attached Images Attached Images
    Last edited by Mark Gibney; 07-22-2022 at 9:37 AM. Reason: explaining photo crowding

  2. #2
    What is your operating voltage?
    Safe to assume you already have 3-ph power available? (manufactured or grid?)

    Allen-Bradley is my go-to for all MCC gear, but Telemechanique is 2nd.

    Traditional soft-start requires 2 contactors, timer, CB, and O/L - - and can get pretty expensive. Never used one, but I recall sales pitch of some 'packaged' electronic soft-starts that are simpler - but still more expensive. If you NEED reduced current start, a VFD is more versatile and about the same cost in 5Hp sizes. (End of VFD sales pitch.)

  3. #3
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    Malcolm, I have 240 volt 3-phase from the utility. I'm in a rented shop in a manufacturing zone, so all good in that respect.

  4. #4
    Some links for info, if you need such:
    https://www.rockwellautomation.com/e...ac-drive-.html

    https://www.rockwellautomation.com/e...starters-.html

    https://www.rockwellautomation.com/e...wye-delta.html

    I haven't looked at the wiring for that motor, but it becomes important for soft-start selection. You'll also need to make some decisions about what control voltage you want to use for a soft-start. I can't offer any specific part numbers w/o that.
    Last edited by Malcolm McLeod; 07-22-2022 at 9:59 AM.

  5. #5
    Link to the 'electronic' style soft-starts I referenced. Never spec'd, installed, used one of the 'flex' versions - available for 240VAC power.

    https://www.rockwellautomation.com/e...ntrollers.html

    I had forgotten, but I have integrated a couple of the SMC-3 electronic soft-starts (long time ago). They're all 480VAC, so won't work for you.

  6. #6
    One more....

    I realized it has been a long time since I have done anything with soft-starts, so I've been reading - - call it professional development.

    StarDelta.jpg
    ^ The right hand of the schematic is what I'm calling traditional; a 6-lead motor needs a total of 9 relay contacts. As you might imagine, these contactors, their interlocks, extra wiring, and controls can get expensive. This took me several minutes to find, presumably because nobody does this anymore and EVERYBODY offers electronic soft-starts now.

    And this is typical electronic soft-start -
    SMC.jpg
    ...and shows why control power decisions are important for selection; the control terminals must match the provided signals' voltage.
    Last edited by Malcolm McLeod; 07-22-2022 at 11:06 AM.

  7. #7
    You could also consider a Variable Frequency Drive over a soft start switch that has the capability to ramp speed upon start and is configurable.

    ESV402N02TXB LENZE 5HP NEMA1 IP31 SMVector VFD (electricmotorwholesale.com)

    Acceleration/Deceleration Profiles
    Two Independent Accel Ramps
    Two Independent Decel Ramps
    Linear, S-Type
    Auxiliary Ramp(or Coast)-to-Stop

  8. #8
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    Due to demand and the numbers produced I would think a VFD may be cheaper then a soft start switch. Espically since you already have three phase input and do not need to oversize the VFD.
    A generic china made 5hp vfd is around $150.
    Bill D

  9. #9
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    Malcolm, the info you provided is way above my pay grade. I don't understand it well enough to use it in my decision making, but I'm sure it's great info! So thank you.

    Mark, from what I gather, VFDs are a little more complex, they do more than what I need, so maybe staying with a soft start is better.

    Rockwell Automation recommend a particular soft start switch that comes out at about $750 before shipping. There's a "refurbished" one on the Bay for a little over $200. Shipping from India. I contacted the seller to ask in what way it has been refurbished.
    Any opinions here about refurbished electronics like this?

    Here are two photos of it -

    Screen Shot 2022-07-22 at 9.33.49 PM.jpg Screen Shot 2022-07-22 at 9.34.08 PM.jpg
    Last edited by Mark Gibney; 07-23-2022 at 11:07 AM. Reason: clarification

  10. #10
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    Quote Originally Posted by Mark Gibney View Post
    Any opinions here about refurbished electronics like this?
    I don't know about industrial stuff like these soft-starts, but "refurbished electronics" in the audio industry is really a misnomer. It just means the original manufacturer tested it and it performed "to specification". Then they just recycle it out to the used buyer crowd. It actually costs them too much money to tear it apart and replace degraded parts such as capacitors (which definitely have a finite lifespan). For $200, I would bet they didn't do anything with it. You're basically looking at a minimum $100 for some engineer to pull apart a device and "look inside". To actually fix/replace parts, the actual cost to manufacturers could be anywhere from $300-600 dollars (you're better off buying it new at this point).

  11. #11
    whats the point to the soft start? Im using machines up to 60 years old original switches and motors. Used by people full time before I bought them, I press a button the machine runs. Just another internet I need thing? Do have one machine Griggio jointer that starts in Delta and switches to Wye I think it is. Other stuff just snaps on and is running full speed in a split second.

  12. #12
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    My Dad's story about soft starts.... They had a large motor driving a vacuum pump. It was hard to start and would trip overloads for the motor. Probably 200-400hp. It was belt drive with 10-12 belts so they cut off one belt at a time until it slipped enough to get started. Sinc ethey use dthis pump only a few times a year it lasted just fine.
    Bill D

  13. #13
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    Quote Originally Posted by Mark Gibney View Post
    Can someone recommend an appropriate soft-start switch to use with a 3-phase 5 hp 1750 rpm motor?

    It's going on a band saw, if that matters.

    Thanks,

    I don't know why the two sideways photos of the nameplate are below the post. I also cannot remove them. Sorry for the duplication.

    motor nameplate.jpg
    Hi Mark, why would you want to soft start a motor that small?

    Regards, Rod.

  14. #14
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    Rod - maybe I don't!
    This thread has educated me a lot on this topic. My initial interest is because several of my machines with 3-5 hp motors SLAM into action, and while I'm putting this bigger (to me) band saw together I got interested in a soft starter.
    I'm within a couple of weeks of firing up the saw for the first time and I'll see how it goes.

  15. #15
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    Quote Originally Posted by Mark Gibney View Post
    Rod - maybe I don't!
    This thread has educated me a lot on this topic. My initial interest is because several of my machines with 3-5 hp motors SLAM into action, and while I'm putting this bigger (to me) band saw together I got interested in a soft starter.
    I'm within a couple of weeks of firing up the saw for the first time and I'll see how it goes.
    Makes sense Mark, you’re probably going to find that with the inertia of the saw you won’t need soft start……Regards, Rod

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