# VFD and 2 speed motor



## jbobb1 (Mar 10, 2021)

I'm kind of confused as to what speed I should set my VFD for. I've read a lot of info and have gotten mixed answers. I'm leaning towards using the lower speed and run the motor above rated Hz when needed, but would really like to hear what you guys think. Thanks.


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## JimDawson (Mar 10, 2021)

Connecting the motor for the low speed is exactly what I would do.  Normally this will give you the best performance.


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## jbobb1 (Mar 10, 2021)

Thank you.


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## f350ca (Mar 10, 2021)

My radial arm drill has a two speed motor. I left the selector switch in place and can run it on either speed. Just don't change speeds while the motor is running, you'll damage the vfd. Techs at Automation Direct confirmed it would be fine doing so.

Greg


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## Ulma Doctor (Mar 10, 2021)

I have a 3PDT toggle switch on my 7x28 motor, it allows retention of the 2 speeds.
as Greg said, it is not switched during operation


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## AGCB97 (Mar 11, 2021)

Just for my own education, what is a 7x28 motor?
Thanks
Aaron


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## cathead (Mar 11, 2021)

My Enco mill switch wore out some years ago so I opted for a VFD.  The motor has two speeds so I picked the
lower speed and at times overclock the VFD to 130 Hertz or so.  It works fine at any speed I desire.  I use the back
gear when drilling large diameter holes and reverse the motor direction.


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## jbobb1 (Mar 11, 2021)

I have a Jet lathe that most of the electronics are pretty much shot, including the 2 speed switch, which is the obvious reason for the VFD.
As Cathead mentioned, I plan to overspeed the motor if/when needed.
I did perform the "Powerup" test today, and everything worked as it should.  Next step is the "Auto Tune".


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## jbobb1 (Mar 11, 2021)

Also, Thanks for all the info/suggestions.


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## mksj (Mar 11, 2021)

It all depends on the motor and if it is a constant Hp or constant torque and the number of poles. If it is a constant Hp, then you use the lower speed wiring (higher pole) configuration and double base frequency to 120 Hz so the speed is the same as it would be in the lower pole wiring. So if a 8P/4P you would use the 8P, and on a 4P/2P you would use the 4P. If it is what as known as Dahlander motor which usually has 1/2 the Hp on the lower speed setting I usually use the high speed wiring configuration at 60 Hz, you will have full Hp, you sometimes give up some torque at low speed setting of 30 Hz but you will have the same Hp as the low speed wiring. Since the VFD can boost torque typically by 150%, I have not seen this as an issue. So the added wrinkle, is I have done a number of VFD installs with Dahlander 2 speed motor's, tried both pole settings and frequently had issues with rougher running despite loading the different parameters and auto-tune for each motor setting. In these installs, I ultimately switched the motor out to a single speed 4P inverter rated motor with much smoother and better performance.  Also, trying to use a single VFD to run both motor settings is doable, but complicated and has no performance benefit in the installs I have done. Factory VFD machines up-size their motors and fewer mechanical speeds. In some applications when retrofitting a VFD motor and going to say a direct drive with a back gear,  you would want to oversize the motor and maybe consider a vector or PM (BLDC or similar) motor.





						How to Install Motor Dahlander on VFD? | GoHz.com
					






					www.gohz.com


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## jbobb1 (Mar 11, 2021)

The motor isn't constant Hp. I had thought about a motor change, but I'm having a hard time with the 1200+ price tag on some that I've found.
I'll change to 4p tomorrow and see how it goes.


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## mksj (Mar 11, 2021)

Try both pole settings, but also worth keeping an eye out on eBay for an inverter type motor or vector type. There are also replacement motors that are inverter rated that run around $400 and will work great.
This is a very popular replacement, Marathon Blackmax and Bluemax, if you have any specific questions let me know.








						Marathon Y551 Electric AC Motor, HIGH PERFORMANCE INVERTER DUTY Series  | eBay
					

Find many great new & used options and get the best deals for Marathon Y551 Electric AC Motor, HIGH PERFORMANCE INVERTER DUTY Series at the best online prices at eBay! Free shipping for many products!



					www.ebay.com
				











						Marathon Black Max 2HP 1750RPM 230/460V 145TC TENV 3Ph 3.4/1.7 60Hz NOP  | eBay
					

Inverter Duty AC Induction Motor; 6 LB FT 5400 Max RPM, 2kW 3525RPM 3 LB FT 460V 3A 120Hz. Due to the multiple quantities available, you may not receive the item pictured in the ad above.



					www.ebay.com


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## jbobb1 (Mar 11, 2021)

I didn't even give Ebay a thought! I'll keep this in my watch list. Thanks!
I know more questions will arise, but I'm trying to get my head wrapped around all of this, so I'm trying to take my time.


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## Ulma Doctor (Mar 12, 2021)

AGCB97 said:


> Just for my own education, what is a 7x28 motor?
> Thanks
> Aaron


my apologies, the 2 speed motor on my 7x28 Vertical/Horizontal milling machine


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## AGCB97 (Mar 13, 2021)

AHH


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## jbobb1 (Mar 13, 2021)

Success!
I got everything connected and it works, Thanks to you guys!
I did have a situation were my heart almost stopped. After completing all the connections, I turned the drive on went to my front panel and pushed the power on button and nothing!
I had forgotten to program A002 to 01: (control terminal).
I do think I'm going to give the high speed a try though.


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