Replacing 3 phase motor with single phase or go with a VFD?
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    Default Replacing 3 phase motor with single phase or go with a VFD?

    Hey guys, I'm new here. Im just looking for advice to see how I should proceed. I have a paper cutter I need to start running in my print shop. It currently has a 3 phase 3hp motor powering it. My new shop doesn't have 3 phase available. Its really the only thing 3 phase we'll ever run. I already bought a single phase motor to replace it, but I wasn't sure if I wouldn't need to rewire the distribution box as well? It obvious has lines T1,T2,and T3 coming into it and leads coming out of them. Nothing on the machine required 3 phase except the motor. Could I just wire up 220v to the distribution box and skip T2 line? Or could I use a 3 pole breaker and wire in 3 hots to each line? That would then be 440v though right? I could also just buy a VFD and have an electrician install it, but in a small town I feel like im not going to get a very knowledgable person on VFD's. What would you guys suggest being the easiest or most economical thing to do? Ive attached a picture of the distribution box on the cutter below. Thanks in advance!

    image0.jpg

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    What is the FLA of the original motor and what is the FLA of your new motor?

    The issue you will run into is motor protection circuitry being unhappy with the extra amps on two legs

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    Quote Originally Posted by AP90 View Post
    Hey guys, I'm new here. Im just looking for advice to see how I should proceed. I have a paper cutter I need to start running in my print shop. It currently has a 3 phase 3hp motor powering it. My new shop doesn't have 3 phase available. Its really the only thing 3 phase we'll ever run. I already bought a single phase motor to replace it, but I wasn't sure if I wouldn't need to rewire the distribution box as well? It obvious has lines T1,T2,and T3 coming into it and leads coming out of them. Nothing on the machine required 3 phase except the motor. Could I just wire up 220v to the distribution box and skip T2 line? Or could I use a 3 pole breaker and wire in 3 hots to each line? That would then be 440v though right? I could also just buy a VFD and have an electrician install it, but in a small town I feel like im not going to get a very knowledgable person on VFD's. What would you guys suggest being the easiest or most economical thing to do? Ive attached a picture of the distribution box on the cutter below. Thanks in advance!

    image0.jpg
    I've used "paper cutters" in a sheet-offset print shop that DID have 3-Phase. If yours is anywhere near the size of our one that cut bulk stock a foot thick at a single go? Baum, built, IIRC. Same as our folder was.

    I hope you had the foresight to use a FIVE HP single-phase, and "TENV" to replace the 3 HP - probably also a paper-dust ignition-source safe "TENV" that it shipped with?

    Single-phase motors tend to get a tad raggedy-ass when worked HARD, so one allows a bit of reserve when converting from 3-Phase...if you want smooth and reliable operation.

    Shouldn't have to mention why "TENV" in a building full of flammables?

    I'd leave the old controls in-place, blocked-off, store the old 3-P motor also documented.

    And simply set a NEW and properly matched single-phase motor-starter for the new motor. Document that, too. Keep a copy in lamination with the machine.

    It will be faster, cheaper, less of a service hassle, going forward, and even rapidly restorable, if/as/when need be. And/or if ever you sell or trade for a new shear.

    "Personally".. given no other 3-Phase need? I'd put a basic RPC up.. with a "TENV" idler. And simply use the shear "as-built". It doesnt' need the variable feature of the VFD, nor even "ramping". Clutch and reduction gears do the do just fine. It does need to retain a "TENV" drive motor.

    And the RPC doesn't even need to be indoors, so one COULD cheap-out on the pain-in-the-FAT-AND-HEAVY-ass but SAFER "TENV" for the idler.

    2CW.

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    TENV or TEFC? At that power level TEFC is probably going to be cheaper and lighter and no less safe. Most Ex motors are a beefed-up TEFC motor anyway.

    Realistically, the motor is not the only/main hazard here. Induction motors generally only produce sparks during a fault (although paper dust on hot windings could self-ignite). Be more wary of your contactors, breakers etc. in the control cabinet, and all the rest of the crap in the same room.

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    Quote Originally Posted by SomeoneSomewhere View Post
    TENV or TEFC? At that power level TEFC is probably going to be cheaper and lighter and no less safe. Most Ex motors are a beefed-up TEFC motor anyway.

    Realistically, the motor is not the only/main hazard here. Induction motors generally only produce sparks during a fault (although paper dust on hot windings could self-ignite). Be more wary of your contactors, breakers etc. in the control cabinet, and all the rest of the crap in the same room.
    Paper dust is an unpredictable bitch. Food for some life-forms. TEFC's tend to clog. See sawdust-production industry as well.



    But let "guys like me" have what we want of either - and in the condition we want it?

    Your building doesn't burn. The roof lands two carparks away and the walls have been flattened!

    Fortunately, offset lithography tends to not support a very "dry" environment!

    At least "not all hours of all days."


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    Replacing 3 phase motors with single phase is a really bad idea. They are not equivalent in any way. Single phase motors have too few torque impulses per revolution and under load they decelerate and accelerate many times during each revolution causing radial vibration. That vibration is bad on drive trains and can leave a herringbone looking surface finish on a lathe during a light final pass.

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    So a few things to consider.
    1. Single phase 220V is single phase 220V, you do not get 440V out of the contactor.

    2. To use a 3 phase (3 pole) contactor for single phase, what is typically done is single phase power comes in on L1 and L2, a jumper wire goes from T2 to L3, the motor is connected to T1 and T3, this assumes there is an overload relay and some will sense a phase loss. Otherwise just use L1 and L2 in, and T1 and T2 out. You still need to change the size of the overload output, and probably need to rewire the whole panel and motor cable to handle the additional current load for single phase and also a larger motor if you go that route.

    3. Power in with single phase, you need to trace back power to transformers or any other sub system and use the two legs to power with single phase. Typically there is a single phase transformer for the contactors and to power other controls or sub systems.

    4. The current contactors are probably matched to the current motor size and 3 phase use, running a single phase 5 Hp motor through the same contactors will result in almost 3X the current and they will probably fail quickly and the wiring will overload and could catch fire.

    5. The overload protection would need to be changed to account for single phase and the increased Hp, so essentially you would need to replace the contactors and the overload protectors. Doable, but requires replacing the contactors and probably adding overload relays on the outputs. An electrician should be able to do this, the contactor and overload relay would need to be sized to the application. You also would need to consider the input current, for 5Hp single phase motor would typically be 50A feed.

    6. TENV vs. TEFC, depends on the dust level and size. Either should work acceptably in this range. A TEFC single phase will be a much more common motor, I would look for a farm duty motor which are made for heavier loads and are sealed to decrease dust and moisture from getting into the motor.

    7. Most likely there are other control sub-systems that need to be powered, these need to be factored into the rewiring solution.

    8. A VFD may be the easiest solution, something like the KBVF-29 is a very simple 3Hp VFD AC drive (no programming) that would replace the motor contactors and overload devices. The motor is directly wired to the output, there is a low voltage for ON/OFF run. You are running at a single speed and the same direction so you do not need any other connections. They are reasonably priced and simple to install. Alternative if you want something more full featured is the KB KBDF-29 or Teco L510-203-H1-U.

    The KBVF-29 is the simplest and most cost effective solution in my opinion and keeps the stock motor. The input wiring may need to be upsized to handle the single phase load to the VFD (10AWG for this model). Single phase motors have more pulsations which can show up as surface finish issues in lathes and surface grinders, but unlikely to be an issue in your application. A farm duty single phase 3 Hp should be equivalent HP wise to your current 3 Hp motor, so I do not see a reason to go to 5Hp single phase and it also may stress other parts of the machine that could cause more damaged if mechanically overloaded.
    KBVF-29 (9593) AC Drives, Chassis Inverter - KB-Controls.com, Your online Shopping for AC & DC Controls & Drives

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    Wow guys, thanks for all the great information. I think i'll probably end up getting a VFD and using the current motor to power the machine. That way 0 rewiring is done. Frankly, we bought the machine at an auction and could probably end up scrapping it for close to what we paid for it. So im not wanting to dump a bunch of money into it. Which a new motor sounds like it would be the most costly after an electrician re-wires it. Im somewhat handy with electrical, but not handy enough to tackle that job. And thanks for the recommendation on the KBVF-29. That is exactly what im looking for. All the other ones kept mentioning all the features which is pointless for my application.

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    There may be people other than licensed electricians around who know how to wire a VFD. Ask a local machinist, if you know one. Indiana is an industrial place, after all, at least the northern part.

    Quote Originally Posted by AP90 View Post
    ... I think i'll probably end up getting a VFD and using the current motor to power the machine. That way 0 rewiring is done. ....
    Uh, think again. VFDs need to be wired directly to the motor. No switches or contactors between. All controls (on/off switches, etc, etc) wired to the VFD, not the motor. Your machine will need to be rewired.

    Before you buy the VFD, best to read the manual and understand it first. Hitching one of these things up successfully requires considerably more knowledge than changing over to a single phase motor or using an RPC. Get one connection wrong and the VFD is fried. Motors are much more forgiving.

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    Gee, i'm going to have to close my shop down since most of my machine tools are 220 single phase up to 7.5hp. I didn't realize I was getting a bad surface finish it must have slipped by me.

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    Quote Originally Posted by tonystoolroom View Post
    Gee, i'm going to have to close my shop down since most of my machine tools are 220 single phase up to 7.5hp. I didn't realize I was getting a bad surface finish it must have slipped by me.
    Dunno there. He might get herringbone-shaped features on the sheared paper....

    7.5 hp single-phase? Must be a *brute* of a motor!

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    FYI, single phase surface finish issue on a lathe which was eliminated with going to 3 phase. Tends to be less of a problem with heavier lathes, but have also seen issues with surface grinders and using a static converter. Not an issue in this application.
    single-phase-surface-finish-lathe.jpg

    Evidently didn't read the KBVF-29 manual, no programming, just adjust some trim pots. Connect power in L1 and L2 of VFD, connect VFD motor terminals to current motor cable and eliminate contactors and fuses. Close low voltage connection for run and one can add serial switches for safety interlocks. Alternative is to wire contactor for single phase and connect to the input of the KBVF-29, set the jumper for auto-start on power up, connect motor output to current motor cable. QED.

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    I've got a little brother to the KBVF-29, bought it with intention of using it on my Bridgeport, 'till the A-B 1305's came along. My KB is on a small pedestal grinder fitted with diamond wheels. While I can SAY that I 'read' the KB's setup documentation, I'll caveat that when I set it up, I just connected the wires, flipped the switch, and fiddled with the pots 'till something happened. Ran it that was for quite a while before re-reading, and I was absolutely shocked to discover that the 'twiddling' I'd done, was in exactly the same process as identified in the docs.

    They're handy little buggers... not what I'd call 'heavy industrial' category, but for small tools, yes.

    7.5hp into a paper cutter... I don't think I'd do that.

    herringbone paper pattern... that's actually the common standard at the Long Wharf market... they tear it off, wrap your fish in it, and off you go...


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