Help rewiring motor from 460 to 208 - Page 2
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  1. #21
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    There is a unknown in these ABB contactors, what is the coil voltage? What is the control voltage of your existing system? I can't see that from the wiring diagram in your post #3. Look at the side of your existing contactor, that will tell you what the secondary of your transformer is required to supply. That could be 120, which I'm assuming.
    I did not see the ABB contactor coil voltage on the ebay listing. The side photo shows B25C for operating voltage, google search I think that is a 440VAC coil voltage, which I don't think you want.
    The contact rating of these ABB are right what you need, 7.5HP at the 208VAC input.
    abb-contactor-hp-rating.jpg

    The problem with the magnetic starter that is complete new box and contactor, what is the coil control voltage of that? I think it's 208/240. If so, you just use the line voltage.
    There is another one on ebay less expensive and would use the remote start-stop buttons.
    MAGNETIC MOTOR STARTER CONTROL FOR ELECTRIC MOTOR 7.5 HP 3-PHASE 208-240VAC 21A | eBay

  2. #22
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    yet another thing I didn't know... I think I understand a little bit better tho. So the transformer is basically just to give a different voltage for the control box but doesn't have anything to do with the motor itself. I will look tomorrow to see what the voltage is on mine, but I think at only $10 more I would rather get the box(the one you linked) already set up for it but I will ask them if it has a different control voltage first.
    So one more questions(sorry) would my current setup work for anything as is, the contactor says 3hp at 230v so would it be good for say a 2.5hp or would it be fine with a 3hp? or is it all trash(other then the start/stop switch hopefully) unless I have 230v/460v?

  3. #23
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    Well I guess I am back to trying to get replacement parts for mine, they responded with "This starter is not very good, especially at 208.
    I highly recommend a square D, Weg or Eaton"

  4. #24
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    Quote Originally Posted by Damon73 View Post
    yet another thing I didn't know... I think I understand a little bit better tho. So the transformer is basically just to give a different voltage for the control box but doesn't have anything to do with the motor itself. I will look tomorrow to see what the voltage is on mine, but I think at only $10 more I would rather get the box(the one you linked) already set up for it but I will ask them if it has a different control voltage first.
    So one more questions(sorry) would my current setup work for anything as is, the contactor says 3hp at 230v so would it be good for say a 2.5hp or would it be fine with a 3hp? or is it all trash(other then the start/stop switch hopefully) unless I have 230v/460v?
    Yes, the transformer is mainly so the system does not run 440VAC out to the stop start buttons. That voltage is scary. So typical control is at a lower voltage. In the case of 208-240, any of the phases to ground will be 120VAC (unless it's the wild phase, read up on that, but you don't want that in your control system.)
    The contactor you have is not junk. It would work fine for a 3HP motor at 208-240VAC.
    I don't think I've seen anywhere in this post what your trying to power that has the 7.5HP motor. Is it going to be running hard at the full rated HP?
    I have a lathe and a 14" table saw that have 3 phase 7.5HP motors. I know I never use them at their rated max. But I do think you need to upgrade your contactor, as eventually the contacts will arc and fail. But if you have the machine running now, your most of the way there.

  5. #25
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    Quote Originally Posted by Damon73 View Post
    Well I guess I am back to trying to get replacement parts for mine, they responded with "This starter is not very good, especially at 208.
    I highly recommend a square D, Weg or Eaton"

    Was that seller comment for the one I linked or your earlier linked starter with the built in start stop buttons. It's odd a seller would point you in a non sale of their item, on ebay.
    I liked the contactors you found ABB brand, but the coil voltage is an issue, that needs to be what your control transformer supports.

  6. #26
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    Its on a abrasive wheel saw? like a normal chop saw but huge so I am not sure if I would every need the full hp. I do want to do the upgrades so it doesn't fail on me when I need it but ya I did turn it on to make sure it worked(bought in unknown condition).

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    Quote Originally Posted by ignator View Post
    Was that seller comment for the one I linked or your earlier linked starter with the built in start stop buttons. It's odd a seller would point you in a non sale of their item, on ebay.
    I liked the contactors you found ABB brand, but the coil voltage is an issue, that needs to be what your control transformer supports.
    It was the one you linked, I asked "On the title of the listing it says 208-240vac but in the description it says 230-240, would it be able to run a 7.5hp 3 phase motor on 208vac? does it require on different control voltage?" and he responded with that...
    I sent the person selling the abb contactors a question on the coil voltage so hopefully he gets back to me and its not 440v. I have been looking at the other ones like WEG 7.5 HP Three Phase Magnetic Starter Electric Motor Control NEMA4X 208-240 V 685650081403 | eBay but they always seem to not be right, this one says 208v 7.5hp but if you look at the pictures it says on the side of the contactor that it is only for 5hp at 200 and 240v

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    This overload and either this 24VAC coil contactor or [url=https://www.automationdirect.com/adc/shopping/catalog/motor_controls/iec_contactors_-z-_starters_-z-_overloads/fuji_contactors_-z-_overloads/32_to_50_amp/sc-e1-110vac]this 110V coil contactor] should be what you need.

    You really need to find out what coil voltage you have. You need to look at your current contactor to do that.

  9. #29
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    You do need to probably unscrew the existing contactor from the enclosure to see what the existing coil voltage is (it will be on the side near the bottom don't know if you can see that from above). That should be easy to see where the connection wires are to the coil. There should be a nameplate, might be stamped or part of plastic casting. These coils are replaceable, so it will be on the coil.
    If the ABB contactors, use that same coil voltage as your current system, the contacts are rated for 7.5HP at 200VAC, so they are just what you want. Ideally 24VAC is a nice control voltage, as running that out to a remote control button enclosure will not give a horrible shock if some wire pulls loose and contacts ground. Either way, an inline fuse is good to protect the transformer from burnout (this is shown on your diagram on the input side to the transformer, and is separate of the 3 main fuses that handle motor current), or damage to the start switch contacts.
    Next you need to look at 3 wire control for start stop push buttons. There you will see an auxiliary contact (4th pole) that is normally open, that is put in parallel with the start button. You can easily find this on the internet. But the idea is the start button energizes the contactor coil, and it is held energized by this aux. contact. The stop button is normally closed, and when pushed removes this power. If you study the electric diagram on your existing contactor, you will see this. It's just learning about normally closed (NC) and normally open (NO) contacts that are provided on some contactors for this purpose of remote control.

  10. #30
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    Sorry didn't see your post before I looked, I cant tell if it said anything about the coil voltage so I took pictures of it and the transformer, if it isn't shown then I will take it apart on Sunday.
    Attached Thumbnails Attached Thumbnails img_20201030_145710.jpg   img_20201030_145742.jpg   img_20201030_145722.jpg  

  11. #31
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    Quote Originally Posted by Damon73 View Post
    Sorry didn't see your post before I looked, I cant tell if it said anything about the coil voltage so I took pictures of it and the transformer, if it isn't shown then I will take it apart on Sunday.

    The control transformer photo #3 shows 110/115/120 on the secondary side. So that's the coil voltage you want.


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