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VFD Info

Hey Guys,
Enlighten me please.

My current mill setup is pulley stacks and belt drive. Now, correct me if I am wrong, but these setups are good because the motor is always spinning at optimal speed and torque. When you change the speed to slower speeds, the motor is working the same, but the spindle speed slows down but the torque goes up. So it is stronger at slower speeds.

With a VFD you lose the torque gains at slower speeds correct?

Under the premise that above is correct, here are my thoughts.

Majority of the stuff I have worked on so far does not need the torque gains and changing the speeds is a PITA. So that is making me interested in a VFD. But, if needed, I dont want to loose those torque gains if I am faced with a situation where it is needed.

So my questions is. Can I set the belts up to the high speed setting and control everything with a VFD, and when needed, change the belts and bypass the VFD?

Also, where is a good place to look for a 1ph 220V 2hp-ish VFD for an affordable price?


Premium Member
I bought a TECO brand VFD an E510 from them - dealerselectric. I'm still working on that project to upgrade my mill. I think it's a good unit and well made. They did however charge me a lot of money for a RJ-45 cable they claimed was a 'ribbon cable' so watch that if you buy from them. The cable is to allow the front control panel to be relocated away from the drive in a handier location.

Here it is in bench testing mode. It's a 1800rpm motor used and sourced from another forum member. I've overdriven the frequency to 90hz and hence the rpm gauge is showing 2700 rpm. I know other people have just bought lower end made in china drives and report good experience with those too - google the forum. People have posted some interesting conversions. My whole setup was probably close to $500 after shipping and exchange and I also bought the big external braking resistor. I think the chinese VFD drives are less. This one is UL listed and I think safety does count for something. This one also supports an input to measure actual RPM and adjust for load - and it also supports a 0-10V signal to allow spindle speed control from a computer. e.g. CNC Mach 3 etc. Lots of extras you might not need. Some people also say for a low end asian one you need to buy it bigger than you need e.g. buy a 3hp if you have a 2hp motor.

So yes you can set the output to 60hz and have the motor turn at normal rate and torque. Then change your belts as usual.

BTW for anyone unfamiliar with these VFD drives you need a 3 Phase motor to mate with the VFD. The VFD drive lets you use 240V single phase current to power a 3 phase 240V motor. The electronics in the drive then let you vary the frequency of the 3 phase power coming out and that controls the speed of the motor.

The VFD has a lot of different strange parameters you can set to tune the motor settings.

I have both vertical and horizontal mills that are pulley driven and have VFDs on both. I find that most of the time I adjust the belts to an intermediate speed and then use a potentiometer on the VFD to control speed. I have both VFDs set to vary frequency from 5 Hz to 75 Hz and the motors will happily run anywhere in that range. At the low end (5 Hz) torque drops off considerably and you have to be a bit careful of overheating because the motor cooling fan is not turning at is optimum speed. That being said, for short periods and light loads it works fine. In cases where I expect more load at a lower speed, I adjust the belts and go from there. I also find that I'm more inclined to set the spindle speed to an "optimum" value when I just have to turn a knob.

So, if you have a 3-phase motor, its a good way to avoid the majority of belt swaps.


Premium Member

So reading this article apparently torque does not decrease as the rpm is reduced. What is reduced is the power which is the torque divided by time . So the horse power is reduced but the motor at 5 rpm is still going to rip your arm off as the torque is the same. There is a graph showing torque vs frequency and horse power vs frequency. It's surprising.

I think here .... now I'm not an 'geer so your mileage may vary ... imagine your vfd turning a boat winch pulling a boat up the ramp. At full motor RPM and frequency you pull it up as fast as the motor can supply the work up to say 2HP. Now you can slow the motor down to half speed and the motor will still pull the boat up the ramp because it's pulling just as hard (same torque) as before just more slowly at 1HP. hmm not making sense is it. Let's try it manually.

Manually... put a big nut buster 18" wrench on the boat winch instead. You can turn it slow or you can turn it fast but you can only turn it as hard as you are strong to move the gears on the winch. Your strength is the torque. How fast you can turn the wrench at that max torque is your max power.

I think we laymen get power and torque all muddled up all the time.


Well-Known Member
Premium Member
Good info @Janger,

I noticed with my sand muller that lowering the speed cam lead to stalls but I think this is due to overcoming the load. Once it gets going you can add more sand gradually and it will run ok

I don't have my pinky ring either and I don't pretend to know the math but your explanation sounds reasonable to me

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Tom O

Active Member
Good info @Janger,

I noticed with my sand muller that lowering the speed cam lead to stalls but I think this is due to overcoming the load. Once it gets going you can add more sand gradually and it will run ok

I don't have my pinky ring either and I don't pretend to know the math but your explanation sounds reasonable to me

Sent from my iPhone using Tapatalk
You can always have a adjustable plow in front of the roller to set how much is mulled in one revolution it will just take a few more revs to mix properly.
Use auctions for 3ph motors. Sometimes you can get a whole pallet. Sometimes you fight with someone over price. But generally most of the time its cheaper then Kijiji by a wide margin.

For example I have two 15hp 3ph motors. Off Kijiji it was like $200 for the explosion proof high eff motor. Off auction it was $40 for a regular TFEC 15hp motor.

Generally 3ph motors are cheaper to get then 1ph as most people have 1ph and industrial folks frequently just buy what they need and don't wait for auctions.

You can of course get into a fight with another machinist over a motor and price will go up.

You can over speed 1800 rpm motor but not 3600 rpm motor (at least not by much). Generally range of 10 - 120 for 1800 rpm motor is acceptable. The range of 5-10 as other have stated is hard to get any good work out of the motor.

BTW there are 1ph VFDs - https://www.wolfautomation.com/blog/vfds-for-single-phase-motors/

Through I think more traditional 3ph + VFD is cheaper.

You can always go creative! 1ph --> VFD ---> 3ph ---> 2 legs on 1ph motor ... see: https://www.practicalmachinist.com/...and-vfd/single-phase-motor-2-legs-3ph-200235/

If you do above report back on how it goes.
You are not the guy named 71HD that fought me over that pallet of old rusty motors that went with fees for $300 are you?

I even remember a user name and its has been like over a month.

Usually my user name is something like tomk on clubbid. Otherwise its a number in 5000 range on michner allan. I now try to go for more estate auctions as the big ones like club bid and especially ritchie bros are over the top expensive to buy.

Maybe we need to organise this somehow through this website - I am always afraid of "friendly fire".