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VFD wiring HELP!!!!

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Forum topic by benk posted 06-27-2011 02:40 PM 2614 views 0 times favorited 11 replies Add to Favorites Watch
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benk

4 posts in 1989 days


06-27-2011 02:40 PM

Hello all! Trying to get my restored 1976 Unisaw up and running and need some help for the “last hurdle”! My saw is of course 3 phase, and i’m running it in a 1 phase shop. I wired a 220v outlet off my breaker box, got a 3 hp capable VFD that takes 1 phase in, 1 or 3 phase out to use as a converter, and rewired my motor on the saw for 220 not 440v. Here is where it all goes wrong…I was inder the impression that since the VFD is putting out 3 phase 220, which it is (checked the plug with a multimeter), that I could just connect it to the existing saw plug and use the saw on/off as it was intented? Will this work? Or do I have to wire the VFD directly to the motor? I ran a 4 wire, correctly rated for the amperage, cord out of the VFD and put a female plug (also properly rated for the amperage) to match the 4 prong plug that the saw’s cord came with. Hopefully someone who has experience with setting up VFD’s can shed some light on the configuration for me? Did I try to make it to simple by just connectling it with the existing plugs? In a perfect world I would be able to use the nice, large, on/off switch that the saw came with but right now I just want this thing to run! Help please! THANKS!!! -BEN


11 replies so far

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crank49

3981 posts in 2434 days


#1 posted 06-27-2011 03:40 PM

I don’t know specific information on your VFD, but, in general those drives have to be programmed (set-up) and have input connections where an external signal, switch closure or other control input, will tell the VFD to start the motor. The VFD will then ramp up the output voltage according to the time interval you have programmed to “soft start” the motor. You stop it the same way. Some drives can even cause the motor to apply reverse power to bring the motor to a stop in a short time. The VFD is normally wired directly to the motor. It can be through a plug if you wish, but the start stop switch in the saw usually is wired to the VFD, not the motor.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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benk

4 posts in 1989 days


#2 posted 06-28-2011 06:32 AM

Thanks for the help guys…next step is to contact the VFD manufacturer and get some details. (the manual is horrible!) I forget the brand off the top of my head, its some tiawan import blah blah blah! Huanyang maybe? Either way the machine itself looks solid and capable of what I need it to do but if I can get it set up. So, the VFD should have been wired to the motor? This is the part I don’t understand. Why would I want to use the tiny on/off switch on the VFD (on the wall 8 feet away form my saw) when I could use the big rockwell on/off switch on the saw? Unless this is not possible. Im sorry to bore people with this, im just trying to get this done without paying an electrician to come out! And I wana hear my badass 1976 3hp Rockwell fire up for the first time! Its a beauty and in mint condition, I got it form a high school for a steal and it was used lightly! Thanks for the help guys! -BEN

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crank49

3981 posts in 2434 days


#3 posted 06-28-2011 07:00 AM

Didn’t say you couldn’t use the big switch on the saw. I said the VFD is usually wired to the motor and the switch could usually be wired to the VFD.

The VFD is the motor controler.
The switch is the HMI (Human Machine Interface)
You flip the swtch and the switch tells the VFD, “we want some power here”
The VFD responds by ramping up the power to the motor.

This means, if you haven’t considered it, that you will have to have at least two control wires between the VFD and the switch on the saw. It may be more.

Again, I must point out, I don’t know the specifics of your exact equipment. I’m just talking in generalities.
You will have to get the specific information you need from the folks who sold you the VFD.
Also, it is unlikely a residential type electrician will be able to help you. This is stuff controls specialists, industrial electricians will be needed for. If you know an industrial maintenance electrician, that is the type of help you will need if you don’t get it from the drive supplier.

Good luck.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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TopamaxSurvivor

17671 posts in 3139 days


#4 posted 06-29-2011 01:56 AM

Sounds like you have a saw that should have a motor starter on the saw. The VFD may or may not pull in the magnetic starter. If it does, there is a good chance you will wipe out the VFD starting and stopping the motor without the VFD knowing about it. i would wire it direct to the motor. You did not say what size your motor is, but the VFD needs to be over sized to run with single phase in.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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Gregn

1642 posts in 2447 days


#5 posted 06-29-2011 02:23 AM

Okay its education time for me, does VFD stand for variable feed delay?

-- I don't make mistakes, I have great learning lessons, Greg

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TopamaxSurvivor

17671 posts in 3139 days


#6 posted 06-29-2011 03:09 AM

Variable frequency drive. It varies the frequency, voltage, amperage and hp of AC motors from 0 to about 150% of rated capacity. Obviously, it is not good to run over 10% for very long ;-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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beginner1

72 posts in 2021 days


#7 posted 06-29-2011 04:51 AM

Ben, you might call your local utility company. The line people might be able to help. Most times its free. Of course I’m in the little town (pol. 3500) of Red Bud,IL. It’s worth a call.

-- Gerald, Illinois

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crank49

3981 posts in 2434 days


#8 posted 06-29-2011 04:57 AM

Thanks for joining in ToPo. The OP (original poster for Gregn ;-)) said he got a 3 hp VFD so I assume he has a 3 hp saw, but you’re right, the drive needs to be oversized in this application.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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TopamaxSurvivor

17671 posts in 3139 days


#9 posted 06-29-2011 09:20 AM

It is kind of hard to really know what the deal is without all the proper info. I think this application just using the drive as a power source with motor switching off and on down stream is asking for trouble. Drives are not made to have loads added and dropped like a transformer is made. Guess there is a reason electricians charge the big bucks :-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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Gregn

1642 posts in 2447 days


#10 posted 06-29-2011 01:42 PM

Thanks Topa, for the info. not that I need to use it, but inquiring minds just need to know.

-- I don't make mistakes, I have great learning lessons, Greg

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benk

4 posts in 1989 days


#11 posted 06-29-2011 07:34 PM

Hey guys, thanks again for all the info! So, my plan is to wire the VFD directly to the motor and get it working, then deal with wiring some Control wires to get the switch on the saw working. We will see how it goes!

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