Who's the VFD guru?

I want to control the speed of a production machine. The drive motor is 1 hp

220v 3-phase 1150 rpm. The motor starts under no load, a mechanical clutch is engaged to run the machine at 100 rpm through belts and sheaves. I want to vary the machine speed down to 10 rpm and up to 120 rpm. The 10 rpm might not be realistic, how slow can I go? What's the skinny? What/where do I buy? It has to be stupid-simple!
Reply to
Tom Gardner
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tom - pretty much any modern VFD can give you a 5:1 speed ratio - 10:1 could be a challenge unless you choose a motor that can tolerate 120 hz excitation, and then you are good to go

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Reply to
William Noble

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are several other VFD units that are suitable. You can program these for soft start/stop, braking, alarms, etc.

They also have vfd duty motors. click on

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I have dealt with these people and they have very good service and value. I have a 120 single phase in / 220 three phase out to run my Emco lathe and milling machine.

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

Reply to
F. George McDuffee

Sounds like a PMDC motor application, not VFD. With encoders and servo control you can go as slow as you like, 1 rev per millenium.

Reply to
Richard J Kinch

Tom, VFDs lose torque below about 75% of the motors rated rpm, the lower the rpm, the greater torque loss.

The trick is to figure out how much torque you need at the low machine rpm and dont go below that.

Lets see here....looks like the motor /machine ratio is running 11.5 roughly at 60 hz

Lets call it 10:1 for simplicity

running the drive motor at double speed is 120 hz, and a motor speed of 2300, and a machine speed of 200 rpm

At 90 hz = 1500 rpm, or a machine speed of 150 rpm

At 75 hrz= 1250 or a machine speed of 75 rpm At 37 hz - 575 or a machine speed of 33.5 rpm

At 18 hz 287 or a machine speed of 16 rpm

at 9 hz 145 rpm or a machine speed of 12,5 rpm

Frankly...In my humble opinion...9hz is too slow ...you will be down to less than .5 usable hp and you will have both torque and heating problems.

going to 90 hz gives you 9 more machine rpm, going to 120 hz gives you

Going up to 120 rpm..thats no biggie. What you may...may want to do, is configure your primary connection pully to run at say...10 rpm when the motor is turning at 200 rpm, and speeding the motor up to say 2200 rpm gives you the 120 rpm max needed.

Ill leave the math to you...my brain hurts after a day welding in 109F temps and its 1:am

Hell..I may not have gotten the math right in the first place..but you get the idea

At 200 rpm, it will keep the motor cool enough, and supply usable torque.

In the worst case, you can use a 2hp motor and drive, and even if you lose 50% of your rated Hp..you are still within range

Automation Direct, the GS1 series are decent enough low end drives..set you back about $200 for a 2hp drive, shipping included

Whatever you do..when you find the max rpm of the machine...read the HZ from the digital read out..and set the program of your drive max HZ output to that freq. This is particularly important if you are going to remote out the start/stop/speed to a control. Else some fumble fingered fucktard will be tempted to speed up the machine to "make production" and over speed your machines ability to handle more than 120 rpm...

Never ever let the hoi poli have programming access to the drive......


Political Correctness is a doctrine fostered by a delusional, illogical liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

Reply to
Gunner Asch

You don't give a lot of details, which you know this group LOVES.

So does it have to be programmable, or automatically change governed by some other thing happening, or is it OK to be "manual". If manual is OK, then it sounds like a job for a Reeves type variable speed belt, similar to what's used in a Vari-Speed on a Bridgeport.

Take care. Good luck.

Brian Lawson, Bothwell, Ontario.

Reply to
Brian Lawson

I'm just back into 8" wheel production, I still owe you but you will have to send your info again, I can't find it.

Reply to
Tom Gardner

I don't know enough to ask good questions. But. The machine will run at

100 rpm +/- a few percent 99% of the time. The only reason to run it very slow is for troubleshooting. I would like to run it at say 60 rpm for training or bad wire. Or, bump it up a bit for a good operator running good wire. It does have a variable pulley that will run it at 60 but it's a pain to get at.
Reply to
Tom Gardner

It does have a variable pulley that will take it down to 60 rpm or so. Would it be good to set the pulley low and run the motor faster for the 100 rpm? Can I use a 2 hp drive on a one hp motor to any advantage? The drive will be locked-up to prevent the operator from diddling it. I don't need soft start or stop or anything other than speed control. Preferably the speed control adjusted from a single pot.

The lowest speed (10 rpm) is for troubleshooting, low speed (60 rpm) is for training and bad wire, and 120 rpm is for a good operator running good wire. Actually, I've never had it that high.

Reply to
Tom Gardner

Tom, motors that are inverter duty rated, have minimum and maximum RPM (or frequency in Hz) stamped. Some VFDs retain torque at lower frequency and some do not. The issue with running slow at full torque (not full power!) is cooling. You can address this with an add on fan.

You most likely can do what you want, with proper selection of a inverter duty motor and proper selection of a VFD.

Also note that at lower frequencies, the motor may run "bumpy" instead of smooth.

Reply to


I did this exact thing on my packing line. You'll be fine just installing a VFD on that motor for running from 30 to 120 rpm. That will get almost all your needs. To go slower, adjust that pulley down. For slower yet, you'll have to add a cooling fan to help keep the motor cool.

I'd just put the VFD inside an electrical cabinet so only authorized people can change speed. Open the cabinet and turn the pot on the VFD for speed adjustment. If you need control on the operator panel, add a 2K ohm pot. You'll want a dry (unpowered) contact from the operator panel that closes when you want the VFD to run.

If you have true three phase, there's no need to oversize the VFD.


Reply to
Karl Townsend

If you go for the low rpm side for long, better mount a muffin fan to cool the motor. I'll bow out now and let the more knowledgeable continue on.


Reply to

Thanks! Please explain the dry contact thing. Can't I just put the VFD between the contactor and the motor? Will a 1 hp motor run right on a 2 hp drive? If this works well, I will put VFDs in 9 more machines. Some of them are 1.5 hp and I was thinking of maybe just get a bunch of 2 hp drives so they would all be the same.

Reply to
Tom Gardner

Yes, you can configure a VFD for "transparent" operation where it starts when powered up. You do loose the dynamic braking ability of the VFD since when you kill the power you get a coast stop, but this is what you get with a motor and contactor anyway so shouldn't be an issue. You can program a soft start if you want. Some VFDs have built in speed pots on the operator panel, others you can simply type in the desired frequency.

As for sizing, yes, a 1hp motor will run on a 2hp VFD just fine. The only time you might have and issue is with a huge mismatch like a 1hp motor on a 25hp VFD where the VFD settings for current limits and whatnot might not go low enough to properly protect the motor.

Reply to
Pete C.

The dry contact is a plain switch. The VFD usually has terminals to provide the power (usually 24 VDC) and common. The switches can start, stop, or reverse the VFD. Check the manual to get the right pot rating if you want a remote pot.

I just started programming the I/O for a new project today. There are about 80 AI's, a dozen or so AO's. 20 or so each DI's and DO's for valves. And the rig will have 21 VFD's. The only hardwired control I'll use on any of them will be an enable tied through a relay to the Estop. AB calls it the Stop signal, but it's wired failsafe, so there has to be voltage on it for the VFD to run. A Stop command is issued by removing the voltage. Speed control, normal stopping and starting, power, amps, and speed monitoring, plus anything else I think of later will be via ethernet comms.

Pete Keillor

Reply to
Pete Keillor

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