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[How do I?] Wire a Two Speed motor to vfd

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wildcatfan

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#1
I purchased a Summit brand (Bridgeport clone) knee mill. Now comes the joys of getting it up and running.
Ive bought and have mounted a single phase 220v to 3phase 220v VFD.
Now the issue is how to wire the two speed motor to allow the vfd to control it.

Attached pictures show the motor data plate, the hi and low speed wiring diagrams, and the current wiring in the junction box on the motor.
I would prefer to leave the factory connector intact for future use since i will eventually install a rotary phase converter to run my hendey lathe i'm also working on rebuilding.

Is it as simple as running individual legs from vfd to each of motor contact as shown on low speed diagram? Or are there other steps involved?
 

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Briney Eye

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#2
If it were me, I would wire to the low-speed terminals and use the VFD to get the high speed. I think you would get more low-end torque than the other way around, but someone may correct me.
 

Superburban

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#3
If you look at the data plate, it is 1.5 HP at low speed, and 2HP at high speed.

I have heard many mixed feelings as to using a VFD to control speed on older motors. I think I would consider wiring it up to a switch, so that the VFD could be switched to either set of leads. Just have to be damm sure not to switch the speeds while the VFD is on. That way, you can keep the motor closer to the speeds it was designed for (Or keep it closer to the power frequency it was designed for, how ever you want to think of it).

Maybe someone knows from the rest of the info on the data plate, if it will work well with a VFD.
 

mksj

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#4
Technically you want a direct connection from the VFD to the motor and no switches. I would recommend leaving the motor switch in the low speed setting and over speeding the motor to 120Hz which will give you the same top speed as before. You would use the VFD low voltage inputs or front panel to run the mill. I would keep the carrier frequency low like 2-4kHz if this is an older motor, this should minimize insulation damage. I have used VFD's with dual motor functions to run both low and high motor settings, but in my experience it has been with less than satisfactory results. If one has a constant Hp 2 speed motor, then they do better to set it on the low speed wiring and increase the VFD top Hz to match the same top speed as on the high speed wiring. As noted above you get more low end torque on the low speed connections, above the motor base speed Hp stays constant to about 2-3X the base speed. Below the base speed Hp drops off in a linear fashion down to 0.
 

wildcatfan

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#5
Thank you for the replies.
The use of an external switch and potentiometer will be done in the future.
For the immediate future i plan to use the panel controls of the VFD to control the motor.

My question really was concerning the actual physical hook up berween the vfd and the motor.
Since the motor is currently wired for 2 speed operation using the factory drum switch, should the leads at the junction box be disconnected completely then wired up only as depicted in the low speed diagram with leads only going to low speed inputs?
 

Karl_T

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#6
I suppose that would be most correct. But you want to be able to go back. Myself, I'd just tape the switch down to low position. Should not hurt a thing.
 
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f350ca

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#7
You can leave the drum switch connected. Just don't switch it while the motor is running. I have a two speed motor on my drill press. The techs from Automation Direct said no problem using the switch. You can have power to the VFD ON, but NO motor power applied when switching speeds.

Greg
 

Briney Eye

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#8
Thank you for the replies.
The use of an external switch and potentiometer will be done in the future.
For the immediate future i plan to use the panel controls of the VFD to control the motor.

My question really was concerning the actual physical hook up berween the vfd and the motor.
Since the motor is currently wired for 2 speed operation using the factory drum switch, should the leads at the junction box be disconnected completely then wired up only as depicted in the low speed diagram with leads only going to low speed inputs?
As others have suggested, you can wire it through the drum switch. Why not start with that just to try it out. Then you can try it both ways by flipping the switch (with the power off) and reprogramming the VFD. I would not leave it that way, though. Once you settle on high or low, pull the drum switch and wire the VFD directly. Taping the drum switch in one position is, to be diplomatic, less than professional.

Experiment with the VFD carrier frequency. Chances are that the motor will be happy with a higher frequency, and maybe you can get it high enough that you won't have to listen to it whistle. I've got both of my VFDs maxed out (14-15khz) because I can't hear that high any more (but I did use inverter-rated motors).

Best wishes.
 
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