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Author Topic: Inverter Duty Motor  (Read 5876 times)

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Inverter Duty Motor
« on: January 19, 2008, 08:58:44 AM »
Hello All,
What is the difference between a regular duty motor and a inverter duty motor ?
What is the risk when using a regular duty motor with an inverter ?
Thanks,
RC

Offline Hood

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Re: Inverter Duty Motor
« Reply #1 on: January 19, 2008, 10:49:25 AM »
The Inverter duty motors have a higher class of insulation, or should I say they are guaranteed to have such a clas of insulation. Some of the older motors may well have had similar quality insulation but no guarantees :)
One other thing is Inverter duty motors often have better cooling so that they dont overheat from long periods of low speed.
 If your motor is reasonable quality I would think you will have no problems running it from a VFD, my Bridgeport motor will be about 26yrs old so it wouldnt have been Inverter Duty and its fine, also the even older  motor that was on  my manual Bridgeport (1974) ran great on a VFD.
Hood
Re: Inverter Duty Motor
« Reply #2 on: January 19, 2008, 10:58:41 AM »
Thanks Hood,
So the only damage that may occur is to the motor ?
No risk to the drive ?
RC

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Re: Inverter Duty Motor
« Reply #3 on: January 19, 2008, 11:16:46 AM »
I suppose anything is possible but even if your motor did short out due to Insulation breaking down your VFD's protection circuitry should kick in and prevent any damage. The protection circuitry on modern electronics is very good, dont ask me how I know ;)

Hood
« Last Edit: January 19, 2008, 11:20:53 AM by Hood »
Re: Inverter Duty Motor
« Reply #4 on: January 19, 2008, 11:44:45 AM »
OK, I'll just trust you on that one. (as allways)
Thank you Hood.

 Next question.

I see that I will need an analog signal converter too. Looking at CNC4pc's C14, it needs a 12vdc - 100ma supply.
My rig has 1- 24vdc ps for the motors and drives, also pulling 5vdc from the usb for the CNC4pc index board.
Where / what is the common way to get 12vdc for the signal converter ?
Thanks,
RC
« Last Edit: January 19, 2008, 05:01:17 PM by Overloaded »

Offline Hood

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Re: Inverter Duty Motor
« Reply #5 on: January 19, 2008, 05:28:35 PM »
On my lathe I have rigged up a secondary PC power supply, its handy because it has plentiful supplies of 3, 5 and 12V. I made up a small relay that is connected to one of the molex connectors on the Computers power supply so that when the computer is switched on the relay is switched. The  switch side of the relay is connected to the Green and one of the Black wires on the ATX connector of the second power supply, works great :)

Hood
Re: Inverter Duty Motor
« Reply #6 on: January 19, 2008, 09:25:23 PM »
Another thing about inverter duty motors is torque and hp constants.  If a motor has a 2:1 Torque constant and base speed of 1800rpm at 60Hz, if you were to drop it below 30Hz or 900 rpm you will lose torque and the same for the hp constant.   But most inverted duty motors have higher constants usually 20:1 so if take 60Hz/20=3 you will have full torque at 3Hz or 90 rpm.  There are also 1000:1 motors.
Re: Inverter Duty Motor
« Reply #7 on: January 19, 2008, 10:45:58 PM »
Interesting.
I DO notice that with the motor I have, non duty, it has much reduced torque at 20 - 30 HZ.
Thanks,
RC
Re: Inverter Duty Motor
« Reply #8 on: January 23, 2008, 03:59:35 PM »
Hello again,
I got the inv. duty motor and pwm voltage converter.
WHAT A DIFFERENCE in low rpm torque ! Thanks DennisCNC and Hood.
This is a small lathe and will not need reverse spindle.
Can I just use a jumper or switch at the fwd input on the drive and NOT use a spindle relay controlled by Mach ?
And just let mach control the pwm to the drive ?
Would this be unsafe ? (no charge pump currently)
Thanks,
RC
Re: Inverter Duty Motor
« Reply #9 on: January 23, 2008, 10:41:55 PM »
^ That will work fine, it might be even more safe because the spindle will never turn by it self unless you push the button or switch.