Operating 2 Motors with a Single VFD

EdCaffreyMS

EdCaffreyMS

"The Montana Bladesmith"
When I decided to modify my KMG to direct drive, I THOUGHT I would have to buy a new VFD (the old motor was a DC motor with DC drive), but thanks to my Pal Steve Kelly, he gave me the info on how to wire 2 motors into a single VFD. It's actually pretty simple, and with Steve's blessing, I built a page on my website to detail how I did it. I'm certainly no expert, and NOT an electrician, but I feel comfortable enough with these sort of things to do the job myself. For about $30 worth of parts, it saved me having to purchase a $400 VFD!

Now, be fore-warned that I likely can't answer questions about different types of setups/applications. I only know that this will work for a KBAC-29D VFD/Controller and two identical motors. If you're looking to do something different, I doubt I can answer questions or be of much help. I would ASSUME that as long as you have a VFD designed to run the largest HP motor you intend to use, wiring in another motor of equal or lesser HP would work....BUT I CAN'T BE SURE....I only know that the way I did it works.

If you intend to do this, READ ALL THE NOTES AT THE BOTTOM OF THE WEBPAGE. The biggest warning I can offer is that when using this setup, YOU MUST ALLOW ONE MOTOR TO COMPLETELY STOP BEFORE SWITCHING THE POWER TO THE OTHER MOTOR! Otherwise you will likely damage/destroy your VFD, and/or wreck the power transfer toggle switch.

OK, that all being said, here's a link to the page that explains how I did it: http://www.caffreyknives.net/1_VFD_2_Motors.html
 
i'm sure this new tutorial will be a great help to many. i wish you had posted this last fall when i was trying to figure out how to do the same thing. it looks like you have included all of the little bits of info that i had so much trouble tracking down. i will say that the motors don't have to be identical, just identically specified (same power, speed, etc...) also, i put my grinder select switch in an off-board box just to make sure that i would not be reaching for the VFD and switch the wrong switch (swap motors rather than turn it off) and hope that muscle memory might save me when the ol'frontal lobe fails. thanks ed, another great contribution to the board!
 
I just go to the hardware store and get two 4 prong outlets and one matching 4 prong plug. Both motors need to be the same hp and the same rpm. Just wire each motor to an outlet and the plug to the cable from the VFD. Then you just plug into the motor that you are using.

I posted this several years ago at: http://knifedogs.com/showthread.php?22285-VFD-question.
 
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i wish you had posted this last fall when i was trying to figure out how to do the same thing
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I didn't even know it was possible....and frankly had never thought about it until Steve Kelly asked... "Why you gona buy another VFD? Just wire both the motors into the one you have!" He was kind enough to text me a short video and some pics.... when I saw how simple it really was, it was a big DUH moment for me. :) The stuff about burning out the switch I learned the hard way, and it was because I didn't allow one motor to fully stop before switching power...... a day or two later I was talking to the folks where I buy my motors and mentioned to them about what I'd done. The gentleman immediately warned me about making sure one motor completely stopped before switching power. He told me that not doing so would "wreck" the diodes inside the controller....important safety tip! :)
 
Wayne Coe said:
I just go to the hardware store and get two 4 prong outlets and one matching 4 prong plug. Both motors need to be the same hp and the same rpm. Just wire each motor to an outlet and the plug to the cable from the VFD. Then you just plug into the motor that you are using.

I posted this several years ago at: http://knifedogs.com/showthread.php?22285-VFD-question.
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I strongly disagree. For safety reasons, power should NEVER feed from a male plug! Also, recepticals and cord caps are built in standard configurations, depending on voltage, amperage, etc. Granted, as long as it's your shop, no one should ever plug something else in, but you'll still want to watch the amp ratings.
 
Wiredued, while I agree, generally, the VFD is off while you are unplugging one motor and plugging in the other so it is not a hot plug.

But if you don't like it that way just get two plugs and one outlet.

Let me know if I can help you.
 
i think the first thing one needs to do is read the VFD operation manual. TECO, Leeson, Siemens, and Allen Bradley all say no switches, relays or contactors between the VFD and motor, connectors are ok. I use Harting connectors because they were available and are easier to use than twist lock style. for safety, motors have male connectors, the VFD female.
 
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