# Southbend 14.5" VFD 3ph to 3ph?



## Trent ks (Dec 30, 2021)

Hi there! Sorry if this is a rinsed question. 

I recently acquired a sb 14.5" x 7 and was thinking about getting a VFD. However since I have 3PH in my warehouse already I have been curious about these 3ph to 3ph VFD's available. I haven't been able to find any posts from others who use them. Would there be any benefit to these 3ph to 3ph over 1ph to 3ph? I don't have a problem switching the belt on my smaller sb 9" so VFD isn't exactly a necessity but I've seen some nice benefits from other users. 

Another question is should I keep to the 1.5 HP book specs for my motor or move to 2HP+? 

Thanks a million!


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## Tom Kitta (Dec 30, 2021)

VFDs are actually 3ph to 3ph. The 1ph to 3ph is an add on feature that many smaller VFDs have, but MAIN functionality is 3ph to 3ph variable speed. Large VFDs are frequently either only 3ph to 3ph or have to be de-rated to 60% if used 1ph to 3ph. 

Small motor at lower RPM due to VFD use will have lower torque then at full RPM (1800) thus it is strongly advised to increase motor size - if you are going to use VFD and run slow - unless you are going to do only very gentle passes.


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## Susquatch (Dec 30, 2021)

Trent ks said:


> Would there be any benefit to these 3ph to 3ph over 1ph to 3ph?



I don't think it really matters. All VFD's take whatever they are fed (1 or 3) and convert that to DC before chopping it up to create a 3ph output with varying frequency. However, I'd bet the 1 to 3 versions are a bit cheaper just because of volume - although I didn't check. 



Trent ks said:


> Another question is should I keep to the 1.5 HP book specs for my motor or move to 2HP+?



I put a 3hp version on my 2hp motor to buy some margin - but I'm not sure if that is what you are asking.


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## Susquatch (Dec 30, 2021)

Tom Kitta said:


> VFDs are actually 3ph to 3ph. The 1ph to 3ph is an add on feature that many smaller VFDs have, but MAIN functionality is 3ph to 3ph variable speed. Large VFDs are frequently either only 3ph to 3ph or have to be de-rated to 60% if used 1ph to 3ph.
> 
> Small motor at lower RPM due to VFD use will have lower torque then at full RPM (1800) thus it is strongly advised to increase motor size - if you are going to use VFD and run slow - unless you are going to do only very gentle passes.



I guess we disagree on both counts! Poor Trent...... LOL!


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## Tom Kitta (Dec 30, 2021)

Susquatch said:


> I guess we disagree on both counts! Poor Trent...... LOL!



Well, we both said bigger motor. I never actually seen 1ph to 3ph only VFD.


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## Susquatch (Dec 30, 2021)

Tom Kitta said:


> Well, we both said bigger motor. I never actually seen 1ph to 3ph only VFD.


No, I said bigger vfd not bigger motor. But I wasn't sure what he was asking. 

My Teco is a 1ph to 3ph and the tech description says 1ph to DC then chopped to 3ph. If you think about it, that's how it has to be. How could you vary frequency without DC in between?  But it's easy to see how you might have thought differently. Also, it seems a lot of us have different views of the advantages. 

I also posted some video of mine making BIG cuts at very low speeds on my Hartford thread. It's impressive. 

The datasheet for the TECO also claims constant torque at low RPMs which is EXACTLY what you want - although others disagree. 

I'm thinking of dedicating a thread to the subject so we can debate the rat poop out of it without hijacking another users thread.


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## Trent ks (Dec 30, 2021)

Thanks for the replies! That pretty much cleared up all my questions I'm very thankful. Verdict is the power in the motor and machine itself won't be affected if its 1 or 3 going into the VFD. 

As far as I saw on the TECO website they do separate the motors into H1 or H3 classes for 1ph or 3ph input which is what got my thinking about it initially. I was looking at the TECO L510 and the 3PH input variety looks like they take around half the amps of the 1PH versions so I suppose it has something to do with power consumption. I do struggle with high amp usage in my space since I only have 60 to share. As far as I can see they both use the IP20 enclosure so hoping it's the same price! 

As far as increasing the size of the VFD itself would 2hp be enough of a margin for a 1.5hp motor?


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## Susquatch (Dec 30, 2021)

Trent ks said:


> As far as increasing the size of the VFD itself would 2hp be enough of a margin for a 1.5hp motor?



Ah, so that is what you were asking..... 

I think it's more than enough. 

In my extensive research on this before buying. I saw two trains of thought. 

1.  A 1:1 ratio VFD:Motor was usually over designed and was plenty. More than that shifted the efficiency curve. 

2. A machine that is driven hard benefits from the extra cooling built into a higher rated VFD than motor. 3:2 was plenty. 

I did not see one single negative other than cost and efficiency. So I went oversized as the cost difference wasn't enough to get my attention and I don't really give a rats butt about efficiency in my little shop.


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## Trent ks (Dec 30, 2021)

Did you order directly from TECO in Canada for your unit?


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## Susquatch (Dec 30, 2021)

No, I got it from E-Motors. It arrived the next day!

I bought another one just recently for my other mill. After the mill is sold, the VFD will be moved to my lathe along with a new VFD rated motor. The second L510 took a day longer to get here.  They get high marks for delivery.


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## Susquatch (Dec 30, 2021)

Quite a few other forum members have the L510 too. I have not heard anything bad about them.

Cheaper units are available but it wasn't something I wanted to take chances with. They are relatively easy to program and they work fantastic. Worth the extra coin if you ask me.

Mine is setup with an external pot for frequency control and an external rev/off/frwd switch. I never tried the auto tune feature cuz it worked great as is.


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## Tom Kitta (Dec 31, 2021)

Think of a VFD as a mini power company. The main reason for oversizing it is to get your motor up to speed faster - as motors need more power at start. You can run large motors on small VFDs but you will not get full plate power out of them. Some people test 30hp motors with tiny VFDs rated at 3hp or so. 

Also many motors can be overloaded at least for a some time - power factor rating. If you have VFD exactly same as motor nameplate it may turn off with overload close to motor HP - not power factor. Hence good idea to go say 20% over. Cost and extra power use are insignificant. Also it is for unlikely scenario whereas you are hogging something off.

As for the motor - bigger size is for slow speed. As motor moves slowly it produces LESS power - horsepower equals torque multiplied by rpm. *H = T x rpm/5252. *So if you run at 15hz and speed is only 1/4 you end up with smaller motor. So if you keep 2hp motor in your lathe, run at 1/4 of the speed you end up with 0.5hp motor. Sure the torque is the same as picture shows but the amount of work you can do - like cutting metal is decreased by a factor of 4. That is a huge drop.


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## Susquatch (Dec 31, 2021)

Tom Kitta said:


> The main reason for oversizing it is to get your motor up to speed faster - as motors need more power at start.



My TECO VFD allows me to program both speed and acceleration for startup (and also for braking at shutdown). But is also limits current to protect itself. So your advice here is good.



Tom Kitta said:


> If you have VFD exactly same as motor nameplate it may turn off with overload close to motor HP - not power factor. Hence good idea to go say 20% over. Cost and extra power use are insignificant. Also it is for unlikely scenario whereas you are hogging something off.



This is the advice I've seen elsewhere. Basically giving the VFD some margin when the going gets tough. If there had been a 20% option I would have gone that way. But the next size up was 50% so I went overkill.



Tom Kitta said:


> As for the motor - bigger size is for slow speed. As motor moves slowly it produces LESS power - horsepower equals torque multiplied by rpm. *H = T x rpm/5252. *So if you run at 15hz and speed is only 1/4 you end up with smaller motor. So if you keep 2hp motor in your lathe, run at 1/4 of the speed you end up with 0.5hp motor. Sure the torque is the same as picture shows but the amount of work you can do - like cutting metal is decreased by a factor of 4. That is a huge drop.



This is a great way to say it Tom. I might be putting words in your mouth, but a corollary to your description is: If you can't, or don't want to, buy a bigger machine to handle the extra "work" of big deep low rpm cuts to accommodate the high surface speeds of big diameter parts on a lathe or big diameter cutters on a mill, a VFD does what it can (within limits) to maintain torque on your existing machine. But you might have to reduce the chip load (make shallower cut or reduce feed speed) to compensate. I think we can all live with that. 

I fundamentally agree that bigger is better. But some of us simply can't afford it, or don't have the room, or can't get it down the stairs. A VFD can't turn our little machines into big ones but it will let our little machines do way more than they could otherwise. The price we pay for that "advantage" is a lower rate of doing work (lower volume of chips) in a given length of time.


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## Degen (Dec 31, 2021)

Something that is important to know is that there are motors designed specifically for VFD's and their curves are flatter.  Before you go Yah Hoo, they are way more expensive.

However, I've converted my mill from single phase to 3 phase and can say considering the slight compromised in HP and Torque, I cab state the benefits far outweigh these.

They include:
-Lower power useage (start up doesn't have high in rush currents), I have seen  drop in power consumption as a direct result, motor start up cost serious power, VFD eliminates it.
-Tweaking the cutter speed for best performance and better cuts.
-significantly increasing rpms that take advantage of modern cutters improving both cut and performance.
-Significantly decreasing rpms to help reduce large cutter chatter.

That all said, form me I like a linear response on VFD, so I set my upper limit at 100 Hz and the bottom at 20 hz (+/-40hz) so when controlled by manually or controller it is equal in both directions.  Second high start up curves should be avoided as loads increase (speeds) more can't keep up and the controller backs off.

BTW my first experiences with VFD's was 30 years ago in the elevator industry having sold the first and second modernization installation in Canada, had to learn a lot to be able to sell it to the customer (and being techie, just loved learning the new tech).


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## Darren (Dec 31, 2021)

Almost all VFD's will accept single phase input, and function fine, even if the data tag says 3ph input. Check the manual, usually found online. You'll have to derate the drive, ie 7.5hp drive becomes a 5hp drive on single phase. You'll have to be able to turn off 'phase loss detection' or similar, so the drive doesn't shut down thinking it lost an input phase.

For small motors like 3hp, the Teco L510 units are great. I have 2 of them. Very easy to setup and operate.  Just be aware that they do not support an external braking resistor.


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## Dabbler (Jan 7, 2022)

I think I really need to clear up a point or 2.  Much of it will end up at the same place.  I know the TECO line very well, have talked to the customer engineers, and even talked to one of the electrical engineers that designed the TECO 510...

All VFDs under 50KW or so take the input and make it into a DC bus. this is vital to getting a sensorless vector drive, or constant-torque VFD.  It then creates artificial 3phase current by pulse width modulation on the 3 legs.

As the RPMs go down, the VFD will be saturating the motor coils by providing full power for as long as possible to help drive the motor at 'near constant' torque.

This can be hard on the motor and promotes motor heating, when the built in fan is moving the least air. (many guys add a fan to blow air over the motor when powered up)

In a milling machine, you can easily use the same rated motor in a 3ph/VFD configuration as you did with a single phase system.  You do lose some low end torque, but that is what the back gear is for.

The situation is very different with a  metal lathe.  @Trent ks Your motor has to accelerate and decelerate the gears and chuck, which can weigh up to 150lbs for a 14/15 inch lathe...  

If you are intending to use the VFD at low frequencies, say at 10 Hz, then you need to step up the motor power to move all that rotating mass. The gear train is inefficient enough you will notice the difference.  You still need to change gears to get low end torque.

There is no problem going to a 3HP VFD and using your current motor and trying things.  For the work you do, you might notice that when turning large diameters, and using very low speeds, you will get extra motor heating and loss of chip capacity.  If this then bothers you, upgrade your motor to a 3HP motor and you will never need more.


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## JohnW (Jan 7, 2022)

dfloen said:


> You'll have to be able to turn off 'phase loss detection' or similar, so the drive doesn't shut down thinking it lost an input phase.



I agree with this comment and the rest of the comments about running a 3ph VFD on single phase.

When running a 3ph input VFD on singe (split) phase, it helps to connect two of the three VFD input phases to one leg of your input power and the other VFD input phase to the other leg of the input power.

Two reasons:
1) By having power on each input phase of the VFD it often fools the VFD into thinking that there are actually three working input phases, so no errors occur. The VFD is usually just checking for power on each input phase, not that the inputs are actually properly separated 120 degree phases. YMMV!
2) The 3ph VFD has three sets of input diodes (one for each input phase). Although one set has to handle the full input power, the other two sets of diodes share the load (if connected as above), so there is usually less heat generated, and what heat there is is spread out more.

When using a VFD, as long as you set the accel and decel times to something reasonable (couple of seconds), there is no significant startup power surge since the motor spins up over a longer time period without massive attempted acceleration as it would when directly connected to 3ph power.


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## Darren (Jan 7, 2022)

I have a 25hp Baldor h2 drive on my SM 1660 powering a 10hp motor. In the manual, it has a section on single phase powering the drive. It says not to connect/jumper to the L3. In the setup options, it has two different options for single phase input, derate the drive, or shutdown. You don't want it to shutdown, but with it jumpered it didn't know it was single phased. That said, I tried it both ways, when I had some cogging issues and i was tuning it out, and there didn't appear to be any difference. So when looking on ebay, find the best deal on a good brand name drive, check the manual, and fire in a sniper bid at the last second and get a great deal.


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## deleted_user (Jan 7, 2022)

Dabbler said:


> I think I really need to clear up a point or 2.  Much of it will end up at the same place.  I know the TECO line very well, have talked to the customer engineers, and even talked to one of the electrical engineers that designed the TECO 510...
> 
> All VFDs under 50KW or so take the input and make it into a DC bus. this is vital to getting a sensorless vector drive, or constant-torque VFD.  It then creates artificial 3phase current by pulse width modulation on the 3 legs.
> 
> ...


Very well written synopsis. The manner in which the VFD rectifies AC voltage and uses a higher DC buss voltage and pulse width modulation to provide constant torque is why I went to 3 ph and VFD. 

I've learned so much as a e-bike enthusiast, like how easy it is to cook a motor climbing hills especially with a dumber motor controller... 

II have a class F inverter duty motor with coils rated for a max temp of 155C, but potential over-heating issues are why I added a continuously operating supplemental cooling fan to our lathe motor as well as adding a 100 deg C snap spring temperature switch bolted to the motor casing to cut the low voltage circuit that powers the contactor to the VFD.  

I am still trying to see if I can add a load resister to absorb the surge in power under load deceleration.  Maybe this is why the cheap chinese VFDs dont stop quickly no matter how they are programmed.


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## Darren (Jan 7, 2022)

TorontoBuilder said:


> Very well written synopsis. The manner in which the VFD rectifies AC voltage and uses a higher DC buss voltage and pulse width modulation to provide constant torque is why I went to 3 ph and VFD.
> 
> I've learned so much as a e-bike enthusiast, like how easy it is to cook a motor climbing hills especially with a dumber motor controller...
> 
> ...



Snap switches are great for temperature control of fans. I'm using some to 'automate' my temporary wood boiler in my shop.

Most cheap vfd's dont support external braking resistors. But, like every other electronic device, i'm sure some hacking can be done. Both my current lathes have mechanical magnetic brakes. Both were easy to integrate into the control scheme of the vfd's

On my big lathe, because the vfd supports it, i use both a braking resistor and the mechanical brake. Mostly to avoid tripping the drive on quick decel, which would happen when i first set it up, where the mechanical brake was not in use and no external resistor. With a heavy 14" 4 jaw chuck, i had to have an 8-10 second decel time, or it would trip. With the resistor I got to 4-5s, with both 2s, easily, from 1500 rpm. 

On my smaller Emco machine with the Teco L510 drive, i couldnt have an external resistor, so i had to set the brake to come on at 19hz, where the lower limit of my pot is 20, so the brake didn't come on when i turned the speed down, so they didn't clash.  It stops very quickly though, even at full speed. Much less inertia. I'm sure if i played around with it more I could make it better, but it works great.


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## deleted_user (Jan 8, 2022)

dfloen said:


> Snap switches are great for temperature control of fans. I'm using some to 'automate' my temporary wood boiler in my shop.
> 
> Most cheap vfd's dont support external braking resistors. But, like every other electronic device, i'm sure some hacking can be done. Both my current lathes have mechanical magnetic brakes. Both were easy to integrate into the control scheme of the vfd's
> 
> ...


Yeah If I had a heavier lathe or turned really big parts I'd consider a magnetic brake. it would be the biggest modifications I've done to date. I love mods.

I'll have to play around with the VFD settings and see how it goes. We just installed it so I haven't been running it on practical projects yet.  I'll see the next 10" diameter roller I turn


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