Variable frequency drive

[jimlll]

There are variable frequency inverters for controlling electric motor rpm?s.
I would like to add one onto a mill/drill.
I believe a three phase motor is required.
Does anyone have experience?
What are your recommendations?

 

[Steve@Advance]

I've installed several, have good success with them.

Can you give more details about what you are doing? HP, voltage, 3 phase to 3 phase, or single phase to 3 phase?

 

[David G]

One note, when supplying single phase to the VFD, you need to buy a VFD with 3 x the HP, so it can get enough energy in.

For example, if 1HP motor buy a 3HP VFD.

 

[Oliver 500 Wa]

One note, when supplying single phase to the VFD, you need to buy a VFD with 3 x the HP, so it can get enough energy in.

For example, if 1HP motor buy a 3HP VFD.

I've not had any issues with going 1.5 x the HP. I'm running 3 of my manual machines on VFDs, a Bridgeport type mill, a 14 x 40 engine lathe, and a bandsaw. Single phase 240V input. Since most VFDs are rated at 208V input, the extra voltage at 240 provides the additional energy needed to maintain the DC bus voltage inside the drive.

 

[jimlll]

Thank you gentlemen for your recommendations.

 

[jimlll]

I have a Taiwanese mill/drill with 1 hp split phase motor.
I have the 1 hp 3 ph motor from my Sheldon lathe, that can replace the mill/drill motor
It?s not easy not easy to change spindle speeds on the mill drill with the pulleys approx 7 ft above floor.

 

[Steve@Advance]

It should suit the application well.

If you're using single phase, like David said, oversize the VFD.

If you need to do a lot of instant reversing, as in tapping, might want to add a dynamic brake resistor and give it a second to stop before reversing.

Haven't bought one in a while but Westinghouse Teco was about the best price, they hold up well.

BTW, when you wire it, be sure to use the controller to stop/start/reverse it, not the existing drum switch.

 

[Geo-TH,In]

David,
I know very little about VFD's. I do there are many different types of induction motors.
Are VFD's limited to certain motors?

Will they work on an air compressor, capacitor start, that requires a lot of torque to start and must come up to speed to disconnect the start capacitors?

 

[jimlll]

I believe a VFD must operate with 3 phase motors. As you probably know a capacitor start motor is a single phase motor.

 

[jimlll]

Again, thanks for the info.

 

[Dusty MI]

Does a VFD driven motor loose horse power when it's speed is dialed down to a rather slow speed?
In other words how well would a VFD driven work on a drill press where it needs lots of power when drilling a large hole?

Thanks
Dusty

 

[Butch(OH)]

Yes, for two reasons. Motors are actually not limited by HP but by amps. When the RPM goes down amps must go up in order to provide same HP. In broad terms a 1HP 1800 RPM motor is only good for 1/2HP at 900 RPM. The other reason is the cooling fan slows down with the motor so a 1HP motor at half RPM will not actually produce 1/2 HP in a continuous operation. The quality of the motor and how much it was overbuilt for the name plate rating comes into play. Most modern European stuff has close to zero tolerance for overloading while an old U framed USA motor will put up with unbelievable abuse.

 

[Oliver 500 Wa]

Many inverters have a function to boost voltage in low RPM operation to help maintain power and keep the amps down a bit.

Many 3 phase motors running on inverters that see use at low RPMs will be fitted with an electric cooling fan so air flow stays constant regardless of motor speed.

 

[buickanddeere]

(quoted from post at 08:49:24 11/29/18) David,
I know very little about VFD's. I do there are many different types of induction motors.
Are VFD's limited to certain motors?

Will they work on an air compressor, capacitor start, that requires a lot of torque to start and must come up to speed to disconnect the start capacitors?

Capacitor start is used in single phase motors . VFD’s with single phase output are uncommon except for some deep well pump applications .
The VFD and sometimes a transformer is used to make single phase into true three phase power .
Applications such as reciprocating compressors should be equipped with unloaders .

 

[tlock0331]

buickanddeere, can you tell me one VFD that outputs a single phase? please include manufacturer and model number.

Again, the motor itself should be rated an F class on the insulation, (as shown on the dataplate) and again, you do NOT have to oversize by 3x's, thats a WASTE of money. double the KW, Amp, or HP rating is all you need, if you need a 2 HP then get a 4 hp, but you HAVE TO BUY a dual rated VFD, NOT ALL VFDS are capable of of switching single phase to "3 phase" because thats not what they do....

and since your working with low voltage, then please try to buy a dual rated motor (230/480v) or a straight 480v motor, and buy the drive accordingly.

other things, if you buy a good drive, you will have to do, is shut off the incoming phase loss alarm, and probably an output phase alarm. if your running a mill or lathe then you probably dont have to worry whether you set it up for constant torque, but you may want to increase the ramp up time, and you may want to set your boost torque setting to around 40% ish.....based on your electrical input at your meter can

just saying....so maybe at best you should look at around 10-17 setpoints that are not factory default to actually make things run correctly and mostly trouble free. That is all based around not causing undue stress on your electrical load and having your wife mad at your for running your milling machine while she, or he, is running your clothes dryer or oven...just doing what i can to make your life easier.

 

[Ken Combs]

I may be wrong, but they lose HP but not torque. The torque is constant and that's what keeps a drill turning, not HP. Since hp is calculated from torque and rpm, it does go down, but that doesn't mean the drill won't keep turning

 

[David G]

The motors are not 3x, only the VFD, as they need additional input to charge the DC bus.

 

[Butch(OH)]

Hi Ken, Your are indeed correct in that the motor torque remains relatively constant but the HP goes down when the RPM goes down when RPM goes down, which was Dusty's question.

As for turning the bit in a drill press your example is flawed. Torque at the motor is not what powers the bit, torque at the spindle shaft is and you cannot mix and match those two values. Example, Say you want to run a 1" shanked down bit in your basic home 1/2" shop drill press with a 3/4HP motor To run the bit at the the correct speed without a VFD will require you to shift gears or belts to run it somewhere around 200 RPM. We will say 180 RPM because it makes the math easy in my example. An 1800 RPM motor requires a 10-1 reduction to get to a 180 RPM spindle and the torque on the spindle raises by that same factor of 10 and the torque increase is darn well needed to properly feed the bit. Unless the drill press was designed from scratch to be VFD driven with no gear changes it will be seriously lacking for torque in the lower speed ranges, that is if a person thinks he can rely entirely on the VFD drive for his spindle speeds.
I once did the calcs for a fellow who was strong willed about never having to mess with his belts on his step pulley Bridgeport and as I remember he was near 10 HP (from 2HP) on the motor and VFD drive to accomplish his wishes. After I priced out every thing required to make it work he got real receptive using the OEM motor long with a VFD and changing pulleys now and then too, LOL

 

[buickanddeere]

(quoted from post at 02:12:10 11/30/18) buickanddeere, can you tell me one VFD that outputs a single phase? please include manufacturer and model number.

Again, the motor itself should be rated an F class on the insulation, (as shown on the dataplate) and again, you do NOT have to oversize by 3x's, thats a WASTE of money. double the KW, Amp, or HP rating is all you need, if you need a 2 HP then get a 4 hp, but you HAVE TO BUY a dual rated VFD, NOT ALL VFDS are capable of of switching single phase to "3 phase" because thats not what they do....

and since your working with low voltage, then please try to buy a dual rated motor (230/480v) or a straight 480v motor, and buy the drive accordingly.

other things, if you buy a good drive, you will have to do, is shut off the incoming phase loss alarm, and probably an output phase alarm. if your running a mill or lathe then you probably dont have to worry whether you set it up for constant torque, but you may want to increase the ramp up time, and you may want to set your boost torque setting to around 40% ish.....based on your electrical input at your meter can

just saying....so maybe at best you should look at around 10-17 setpoints that are not factory default to actually make things run correctly and mostly trouble free. That is all based around not causing undue stress on your electrical load and having your wife mad at your for running your milling machine while she, or he, is running your clothes dryer or oven...just doing what i can to make your life easier.

Oh Yea of little faith . Franklin Mono Drive https://franklinaid.files.wordpress.com/2011/09/image-111.jpg

 

[kevinstuff]

If it?s to slow down a drill press ,
Then what I found was a 1170 rpm
single phase motor , and they are also made
in three phase. It took awhile to come across
one , but they are out there. And in three phase
there are 900 rpm motors