Thread: VFD Suppliers

Originally Posted by Bryan

Ray, to what extent can using a larger motor compensate for this? I doubled mine from 1 to 2 hp and was hoping that would be enough. Haven't used it enough yet to really comment on performance.

PS: Eskimo, yes Dave has a better use for it.

Hi Bryan,

Going for a 2hp motor was a smart move.

I think it will work just fine, it all depends on what Hz the vfd is running at, let's say you are running at 50%, (25Hz) then you will still have 1hp available (roughly).

Where you might notice the drop in power is say you have the gearbox selected to 1000 rpm, and dial the vfd down to give 100 rpm, the vfd would be running at only 5Hz, you would find it hasn't got much torque, might still be usable for light cuts..

Next time you are on the lathe, give it a try, and see how slow you can go, with a high gear selected. I'm sure that there are a few others here, (myself included) who would be interested in what your thoughts are.

Regards
Ray

Originally Posted by Stuart

Ok I think I am even more confused. At 0 rpm even infinite torque delivers 0 power. At 1 rpm the torque would need to be 1440 times what it is at 1440rpm(right?)

Let me think about that for a bit, now I'm confused...

FWIW my lathe is a single speed belt driven with a 4:1 back gear. I am replacing its obsolete 2 hp. motor drive with a 4 h.p. induction motor. At 145 motor rpm (35 spindle rpm) it will be at around 5Hz. I figured I would need at least a 4 h.p. motor to get the required torque at that low speed. (.4 hp resulting X 4 (back gear ratio)= 1.6 h.p

I also have a 2.5 kW AC servo motor that I want to migrate to, but that has its own issues (inertia mismatch between the servo and the load).

(The above is the 1:1 motor:spindle ratio case, and I don't want to give up too much top speed. The lathe originally had 45-4000 rpm range. I don't want to go to 160 Hz+, but I would go to 120 Hz if the drive train balance is OK)

Greg

Originally Posted by Greg Q

That one seems* to be a vector control (constant torque) model, and worth the extra money if it is.

*Seems to be because many VFD sellers are now using "vector drive" and similar terms to convince the unwary that the drive is constant torque when in fact its V/Hz.

I guess a question to the seller should resolve that one way or the other since he's here in Oz.

Greg

Too late - I ordered it on Tuesday afternoon and it was waiting for me when I arrived at work this morning. Techo Mark and I are going to try it later this afternoon - I'll report back as soon as we have something worth saying.

[EDIT] Nothing much to report other than it works as it says. We've played around a little with the setting of functions and that seems straight forward enough.
Mark is going to help me setup a switch box and bits and pieces so I can't quite plonk it on the lathe yet.

Originally Posted by RayG

Where you might notice the drop in power is say you have the gearbox selected to 1000 rpm, and dial the vfd down to give 100 rpm, the vfd would be running at only 5Hz, you would find it hasn't got much torque, might still be usable for light cuts..

That might actually be an advantage for parting. Better to stall than break stuff.

Next time you are on the lathe, give it a try, and see how slow you can go, with a high gear selected. I'm sure that there are a few others here, (myself included) who would be interested in what your thoughts are.

I can provide my freq/rpm data but not much in the way of thoughts at this stage. I will report when I've had a chance to use it more.

These are the upper and lower spindle speeds for each pulley combo (at 5Hz and 70Hz):

1: 42-628
2: 56-845
3: 71-1116

Lots of overlap. I reckon I can leave it in any of those ranges and get most things done, only belt swapping for the extreme cases. It's a lightweight machine and I don't push it hard.

Originally Posted by Greg Q

<snip>
I also have a 2.5 kW AC servo motor that I want to migrate to, but that has its own issues (inertia mismatch between the servo and the load).

Now your'e talking real motors..... what brand? Does the controller have auto-tune?

Regards
Ray

Hi Ray...I have a pair of Allen-Bradley servos and drives, cables etc.

I collected them over a couple of years on ebay, and I am planning* to install the small one on the Deckel feed shaft to replace the chain driven shaft and change gears (Which I do not own).

*Plans change though, and there's a chance of another mill on the horizon. If that happens I'll keep the FP-1 for manual duties and leave the feeds as they are.

The whole subject of inertia mismatch came up in a PM thread. I may be OK, but the servo is pretty small compared to an induction motor (although just as heavy). I was lucky enough to buy everything new at less than 10% of new price, including some massive braking resistors. My lathe has a camlock chuck, so quick stopping won't be a problem.

Greg

Originally Posted by wbleeker

Some good info here, thanks! While were are talking about VFD's Where is the best place to get a motor I am looking for a 1.5kw.
Will

Will,
try these guys:

Electrical Motors,3 Phase Motor,Gear Motor,Industrial Electric Motors by Royce Cross[cat1]=-1&Variable[cat2]=-1&Variable[cat3]=-1&Variable[searchfilter]=-1&Variable[sqlFilter]=-1&pager=1&startpage=1&Variable[cat1sel]=-1&Variable[cat2sel]=-1

Their prices are on the website. I spoke to them today. They said "about" $25 postage for a 10kg motor (1.5HP 3 phase) to Melbourne.

Originally Posted by Greg Q

The whole subject of inertia mismatch came up in a PM thread. I may be OK, but the servo is pretty small compared to an induction motor (although just as heavy). I was lucky enough to buy everything new at less than 10% of new price, including some massive braking resistors. My lathe has a camlock chuck, so quick stopping won't be a problem.

Greg

Can you find a link to that thread, it would be interesting to hear why anyone would think low inertia was a problem. Servo motors are specially designed to have low inertia, that why they are often long skinny things, it's so they can accelerate and decellerate faster.

The trick is to be able to tune the PID, I would expect a top of the line AC servo like Allen Bradley would have some auto-tune function.

Regards
Ray

Originally Posted by RayG

Next time you are on the lathe, give it a try, and see how slow you can go, with a high gear selected. I'm sure that there are a few others here, (myself included) who would be interested in what your thoughts are.

I can report that in high 'gear' (pulley), at 7 Hz it's quite easy to stall. At the same rpm in low, at about 12 Hz, no problems. I was facing 75mm bar at 100-odd rpm. The cut was modest, but interrupted.

Hi Bryan,

I'm finding similar things on the surface grinder cross feed, the torque drops away around 7-8 Hz, so I think for a rough guide to gear selection, you might get (say) 10 Hz to 70 Hz range for each gear ratio. That's a 7:1 ratio, still plenty of flexibility and would mean far less gear changes overall.

Regards
Ray

Ray, yes I agree it's a vast improvement. However it's not a total solution for a lack of change gears. Not the way I've done it anyway. If I add another motor pulley to get 6 speeds instead of 3 it will be better.

BTW have you played with PD145 - auto torque compensation? I've set mine to a cautious 6 out of 10 so there's a little room to move.

Ray, where does 70Hz as an upper limit come from and is that for a 1450 or 2850 rpm motor?

I was discussing this with an electrical engineer at work and he was suggesting that almost all electric motors are designed to cope with at least 3000 rpm and if we think about 60Hz motors then 3450 rpm since I don't see motors made for 60Hz being any different mechanically than our 50Hz motors. So a 1450 rpm motor mechanicals should theoretically be able to cope with 1450/3450 x 50 = ~120Hz.

The mechanicals of a lathe are them probably the limiting factor of actual maximum rpm but if the lathe is operated at say a lower gear ratio then this effect is reduced.

Anyway - just exploring the origin of the 70Hz.

Bob, 70 Hz if an arbitrary figure I've used as an upper limit for 2 reasons: I don't need more top end, I need more bottom end. And the motor is in retirement so I'm just being conservative. Jim Cox suggests 1.5 - 2 x nameplate speed should be quite safe. And I'm guessing he's being a bit conservative too. See "Electric Motors", Workshop Practice Series No 16, p62.

Originally Posted by Bryan

Bob, 70 Hz if an arbitrary figure I've used as an upper limit for 2 reasons: I don't need more top end, I need more bottom end. And the motor is in retirement so I'm just being conservative. Jim Cox suggests 1.5 - 2 x nameplate speed should be quite safe. And I'm guessing he's being a bit conservative too. See "Electric Motors", Workshop Practice Series No 16, p62.

Thanks Bryan.