MOTOR VFD UPGRADED ON BELT DRIVE

[Cruiser]

Howdy Fellow IH'ers,
Some time back, I did the belt drive conversion on my IH and then complained about loosing all my low end torque. I had some things to learn and bought the motor & VFD before doing my proper home work. There were a few others talking motors and VFD'd but I didn't fully understand what they were telling me !
First off I started with a motor recommendation that was 2hp, 3470rpm motor and I thought to myself, SELF ! ( this parts gets me into lots of trouble) I want to increase my top end speed !
I also purchased a Hitachi L200 vfd. It is a good unit, BUT !
What I recently learned, and a few others was trying to tell me, and I really needed to know was this !
The 3470 motor falls into the 3600 group & is two pole, great for high speed, no low end torque.
next group is the 1800 or the 1740 motors, four pole ! ! ! This is the work horse motor for our needs. 1740 rpm's and lots of low end grunting torque !
then there is the 1200 6 pole, 800 8 pole etc.
Another thing I didn't know was that there is the std motor, and the inverter grade motor, which mainly is of a better grade of insulation and core bonding, wire etc.
Enough of that, but, If I had been able to read the above before I purchased my motor and vfd, I would have been much happier from the get go ! I could have made a more informed decision, that's why I'm posting this.
My 2 pole motor on the L200 ran great through the gear box, no problems. But when I went direct belt drive and eliminated the gear reductions, If I slowed the motor down to 20hz (20hz of 60 hz) I could grab the spindle with my hand and stall the motor, NOT GOOD !
OK, I just bought a four pole motor, C face mounting, still 2 hp.
Also bought a Hitachi SJ200 inverter drive which is the "Constant Torque" model, and started to test things out.
I left the 2 pole motor on machine and replaced the L200 with the SJ200 & set up the drive with the goodies turned on and set for two pole. I could still stall motor with hand and saw no real difference with drive and started worrying about $ spent.
I started the change over to the 4 pole motor, (used, non inverter) I had to make an adapter to extend shaft in order to eliminate the other shaft in box, then since the motor was C face mount I needed to be able to bolt to motor from inside of cover plate, then got it all assembled and mounted.
All I changed in vfd was from 2 pole to 4 pole then ran motor. Sounded great, I slowed it down to about 8hz which is about 230 rpm and tried grabbing the spindle.
I'M HAPPY TO SAY IT TRIED TO RIP THE PALM OFF MY HAND ! Now torque up the wazoo, I couldn't even hear an audible drop of rpm's.
Now I had my low end torque and could start to fine tune the inverter, but first, The SJ200 can over drive the motor from the 60 hz up to a limit of 400hz ! But, since my motor is not inverter graded and may have other limits, I chose to limit my input of 120hz, Now, I still have my 6000 rpm spindle and also my needed and wanted low end torque.
There are numerous smart and all knowing people on this site. And they knew all this stuff when I was just starting on this project. But, what I try to say above is not what they were saying and so I couldn't even put together an intelligent question in order to make sense of it all. I hope this can help someone who finds themselves in the position I was in then.
There is more yet to learn, more fine tuning of the vfd, more terminology to absorb, more questions to answer . . . . . . . . . .
I hope this makes it easier to understand, so maybe that someone, will not have to blunder the way I did, to learn what others consider to be fundamental !

[banctecbobn]

Your post was most informative and with perfect timing. I am looking into a VFD upgrade for my Shoptask and would have made the same mistakes you outlined. I like it when someone post information on actual personal experience and not just what they think will work.

[mactec54]

Hi Cruiser

Something you were doing is not right because your motor you have now is 1740rpm @60hz taking this motor to 120hz will only give you 3480rpm not the 6,000rpm

You need almost 2/1 belt pulley drive to get to the 6,000rpm with this motor

There should of been nothing wrong with your 2 pole motor, with 1/1 belt pulley drive
It's all in your pulley sizing to get the gear ratio correct for each motor

Both will do the same thing if set up pulley wise to suit each motors rpm

[Cruiser]

The 6 grand is spindle speed !
I got some gear ratio involvement in the belt drive !
thanks for the math lesson tho

Again, The two pole motor had NO low end torque ! I could stall it by hand ! this was tested with the new SJ drive !
The four pole motor has BALLS ! I tested it in cut today and with a 3/4" old dull hs tin end mill and it grunted and threw chips !
I don't think saying that there should be nothing wrong with the 2 pole motor after running this test is saying much, The two pole motor just don't have any LOW END PERIOD !
trying the same thing with both motors and seeing the results first hand, WELL !
The four pole was run this morning in cut doing a .15 dp x .025 with rpm at 7.1hz or 500 rpm and didn't slow down at all.
The old motor, well, I could stop it with my hand so what else can I say

[mactec54]

Hi Cruiser

Mostly 2hp 2pole motors are on Bridgeport CNC knee mills (there standard motor) & you can not stop them with your hand at 500rpm & that is 1/1 pulley ratio so you had something wrong with your set up for this to happen, It may have been the drive but I think you had the wrong pulley ratio

I have to agree that they don't have a lot of torque right up to 1000rpm but they can still plunge cut a 1" endmill at that 1000rpm

If you put your 4 pole motor at the 2/1 pulley belt ratio to get the 6,000 rpm you will have the same problem as you had with the 2pole motor

You can't have the 2pole & 4pole motors at the same pulley ratio, You can but they won't perform the same at the same pulley ratio

The thing is if you want speed lots of rpm you go with the 2pole & have a low gear or 2 pulley sets so you change one to high speed & one for the low end rpm

The 4pole you would have to do the same thing if you want high rpm you can only drive it at 120hz above 120hz on a standard motor & it will not last very long

[Cruiser]

The Bridgeports that I ran had a dynamic drive and when slowed down the belt ratio was reduced and the motor stayed at top rpm !
If that were my case I'd agree with you.'
My belt ratio is 1.76 to 1 or close to that (memmory issue) and does not change.
If something was wrong with the motor I don't think it would wind up to full rpm, or it would run with lost phase rumble. this was not so and it was gutless at low rpm from day one.

[mactec54]

Cruiser
You have not seen my Bridgeport head conversions, these have been running for many years they are a 1/1 drive 2pole motor

[Cruiser]

Well then, Either my motor was defective from the factory or you have a differant type of motor than mine.
Other than that then your drive must be a lot more potent on the bottom end of the scale and the motor can take it.
I don't think my old motor is inverter duty and I know my new old motor is not and if your motor is a newer inverter duty or maybe a vector drive motor then I don't know.
What I'm trying to say is we must be talking oranges and tangerines here !
The motor ran great at top speed but had Zero low end torque. The new motor has great low end torque.
What ever the case we are not both on the same page !

[mactec54]

Cruiser
The motors are standard Bridgeport motors 2pole, & are not inverter duty, the vfd drives I use are general purpose Yaskawa drives nothing special here, but they are very good drives

Was your biggest pulley on the motor or on the spindle

[Cruiser]

Big wheel is on the motor, it is set-up for getting rpm's useable for alum. to spindle.
question ? what is the rated rpm of this motor of yours ?
Is it 230v ?

Never mind the questions, I saw one of your threads.
I conceed, something wrong with other motor ! (no low end capacity)

[mactec54]

Cruiser
There may of been something not right with the motor but your pulleys should of been the other way round for the 2pole motor you were gearing it up instead you should of been gearing it down the 2 pole motor would of been running to slow to have any torque at 500 rpm

If your ratio was with the small pulley on the motor & the large on the spindle (1to1.76 ratio)your rpm would of been 5441rpm at 120hz ( these numbers are all aproximate )

So at 500rpm at your spindle the motor would of been doing 880rpm which would of had much better torque & most likely you would not of stopped it with your hand

The motor would of been running at around 284rpm with the big pulley on the motor & the spindle would of been running at 500rpm you can now see were the problem was with the motor speed at 284rpm you sure could stop it very easy but at 880rpm it would of been very hard to stop

[mactec54]

Cruiser

Some more for those that want to change there machine to belt drive It does not matter if you have a 2 pole motor or a 4 pole motor if you have the gearing/pulley ratio correct & the right VFD to do the job

If you are wanting around 6,000 rpm, then the ratio for a 2pole motor needs to be around 1.13/1 on a 3470 rpm motor this will give you 6,141rpm at 120hz, the biger pulley goes on the spindle, (all numbers are approximate)

If you have a 4pole motor with 1740rpm & want the same rpm then the gearing /pulley ratio will have to be 1/1.76 this will give you 6124rpm at 120hz, on this one the big pulley goes on the motor, ( all number are approximate)

There are other things that come into play as well, your VFD drive will also have to have the correct set up & right rating to drive your motor

If your VFD has a 230V 3ph input & you want to run it on 230V 1ph then if your motor is 2Hp your drive would have to be 4Hp rated or more usually it would be a 5Hp rated drive to do the job

If you buy the right drive for single phase rated input your drive then can have the same Hp rating as your motor