Vfd motor matching

[bigrockcandymountain]

Ok so i have a lathe lined up.  It has been outside for 15 years but it is free and seems like it will be ok to start with.  It is about 18" swing. I'll do more details when i move it home in the spring.  It is frozen down for the time being. 

Anyway, i would like to power it with a vfd.  I found one that has specs as follows.
Input 200-240v 22a single phase
Output 10a 3 phase 0-300hz no voltage stated but i assume 240v

It is near me and less than $200 on Ebay.  It is weg brand, not chinese.

Here is the motor dataplate on the lathe.

What do you guys think.  Is it likely i can rewire this motor for 220v? I didn't look to see how many motor leads it has.  What is with the 2 speeds stated? And the 2 amperages?

Thanks
Derek

[bigrockcandymountain]

I should add that i understand that 10a at 240v is only half the power of 10a at 440v.  My inverter only puts out 4400w continuous so I'm hoping to just run the existing motor at half rated kw and take lighter cuts than you normally would on an 18" machine

[mab]

I'm not sure I can help much - that motor rating plate isn't telling me much - is the CAV the hp rating? I would guess it could be wired for 230, but as it's a dual speed motor you may find there's more wires inside than you can make sense of - but it may be worth having a look as there might be a wiring options diagram in there too.

The output voltage of the vfd will depend on the frequency - at very low speeds the voltage will be <<230.

If the vfd input is 22a @230v then that may translate to approx 10a @440v 3ph; also approximately matches your inverter rating. I'd be tempted to try it as is - but you may want to wait for more knowledgeable advice before following mine.

[bigrockcandymountain]

I did a bit more digging and cav is for cavallo which is horse in italian.  So yes it seems it is 7hp at 1700rpm and 9.5hp at 3400rpm. 

I'm going to wait on the VFD i think and just try running it at 240v 3 phase. 

The lathe will do 76 to 1600 rpm with 3400rpm input.

With 1700 rpm input it will do 38 to 800 rpm. 

I could just put a single phase motor of either speed on it and put up with less speed options.  I kind of think the high speed might be better for what i will mostly be using it for.  My inverter would probably run a 5hp fairly easy. 

[ruddycrazy]

Quite a few years ago when I setup my machineshop  using VFD's the biggest single phase to three phase was 3hp max, anything above that is three phase to three phase. Things may of changed over the years though but I do doubt there would be a single to three phase 7hp one out there.

Cheers Bryan

[bigrockcandymountain]

Thanks Bryan,
I have since done a whole lot of thinking on this and i have decided to keep it simpe for some experimenting.  I have a 4 pole 3hp single phase motor sitting on the shelf that i will mount and make some chips.  I will be limited to 800 rpm max.  That should get me started, so i can get a feel for what i really need.   

I'm thinking ultimately the best might be a 3 phase 5hp 4 pole motor with a vfd so i can drive it 120hz.  I would like to know for sure though before i spend any real money.

I think you are right that single phase vfds only go up to 3hp.  The china ones go to 5hp which i assume is just 3hp with Chinese over rating. 

I understand you can use a 3 phase input vfd with singe phase input if you derate it by half.  So i would need a 10hp. 

[machinemaker]

If you are looking for VFDs or other components I have had good luck with: automation direct and factorymation.
Kent

[SparWeb]

Hi BRCM
I currently have a very heavy plate chucked into my little lathe and it takes a while for it to come up to speed.  Presumably the current is higher than the nameplate until it settles.  I could measure with a clamp-on ammeter to get you an idea what a heavy lathe start-up load looks like.  Scale up from my small 12" machine to this one of yours.

[bigrockcandymountain]

Ya that would be great.  The running amps etc is pretty easy to calculate, but the starting inrush current is quite a bit harder to predict. 

Thanks machinemaker for the tips.  I'll look those guys up if i decide to go the vfd route. 

[SparWeb]

This was fun.

My lathe has a 2HP motor running on single-phase 240VAC, so make adjustments accordingly.  Because of the mucking about I'm doing to mount a 4-jaw chuck, you caught me right in the process of going from facing the new backplate to removing the 3-jaw chuck entirely.  So I was going from heavy load on the spindle to no load and back.  Perfect time for a comparison test.

I measured a bunch of things together to get an idea what's going on.  No Load:
Speed 287 RPM
Line Voltage: 246.0 VAC
Startup Voltage drop: 242.2 VAC
Startup Current Peak: 32.4 A
Running Voltage: 244.4 VAC
Running Current: 6.2 A

The result is that the input power to the lathe is 1.5 kW (2HP exactly) while it's running, and the inrush goes up to 7.8 kW (10.5 HP) at the moment of startup.

Then with the chuck on and a circular plate almost as heavy as the chuck:
Speed 282 RPM
Line Voltage: 247.0 VAC
Startup Voltage drop: 242.4 VAC
Startup Current Peak: 36.1 A
Running Voltage: 244.7 VAC
Running Current: 6.5 A

Now it needs 1.6 kW (2.1HP exactly) to run, and the inrush went up to 8.8 kW (11.7 HP) at startup.

Just for fun I switched up the speed to "575" RPM though it actually ran at 562 RPM.  Now it needs 2.4 HP to run and 13.3 HP to start.
The startup inrush current was 41.3 Amps.  My breaker is 40!  I haven't tripped it.

Conclusion: The ratio of inrush/nominal current is about 5x in light loads, and about 6x for heavier loads.
I bet I just proved a bunch of stuff I could have looked up in a book.

[ruddycrazy]

Depending on the brand of VFD you get some can be programmed so the electric motor wired in Delta thinks it's a larger motor. I just run 2hp 3 phase motors on my 4' lathe and my Bridgeport mill and both are programmed so the motors run at full torque even on low hertz settings. With my Bridgeport I just run a single V-pulley and programmed the VFD to run at 100 hetrz and setup a 3 wire interface so start/stop, 5K pot for hertz control and forward/reverse. With my lathe I got the rolls royce VFD which has a jog feature so I set that up on the lathe.

Now sometimes I set the VFD on the lathe to show the current and on startup it rarely goes over 7 amps and all of my machines run happily off my 3Kw Kipoint inverter thats over 15 years old.

With my toolroom lathe it came with a 3 phase motor so I just wired it up in Delta and put a smaller VFD on along with the 3 wire interface, now as this lathe does have a speed lever when the vfd is set 100 hertz and the speed handle is turned up the rpm on the toolroom lathe is around 4,000 rpm. This is perfect for machining small diameters and this lathe has a collet setup. I have 3 Burnerd grip true 3 jaw chucks which when set better than a thou accuracy repeatedly. this lathe doesn't have a quick change gearbox so everything is change gears and as it's a German toolroom it is one accurate lathe. 

[Warpspeed]

One major advantage with a VFD is that you can program in a gradual starting up ramp. The motor probably needs a couple of seconds to reach final speed anyway, even if you hit it with the full 240v instantly, and suffer the massive resulting current surge.

If you program in a more gentle starting ramp of perhaps over a few seconds, the current surge can almost disappear, and its much kinder to any inverter that may be doing all the work.  It also gives fuses and circuit breakers a bit more of a chance as well.
Not only that, it may be possible to run a more powerful motor with a VFD, as its often the starting surge popping fuses or breakers that  limits what may be practical.

[bigrockcandymountain]

You are right.  Mine is set to ramp up over 10 seconds and that works great.  That's running a 5hp motor off of a 4.4kw inverter and a 15a 240v breaker.