Thread: Another VFD & 3 phase question

Originally Posted by toolman49

G'Day Simon,
Thats one serious mother of a motor, The KBMM 240 controller is rated at up 3 H.P. (16Amps @ 180 volts D.C.) when fitted with the auxiliary heatsink, Depending on how hard you intend to push the motor it would probably do the job.
Regards,
Martin

Hi Martin,

I think it was probably quite expensive in it's day. It has a dedicated and separate 240V AC cooling fan at one end. How do you think a 220V DC motor would go on a 180V DC speed controller? I'm thinking it may actually be OK since it's all current limited by nature? I get the impression that DC motors in general are not as fussy about being run on reduced voltage, unlike their AC counterparts. But I could be wrong, I'm still learning about this stuff.

Also, if you don't mind me asking, what is a KBMM 240 controller worth?

Cheers,

Simon

Simon,
get the one with the pot for an extra $9. Sooner or later you will want to fit one later anyway - and its likely to cost around $9 for the pot and the knob.... my first one cost more that that.
Joe

Hi Simon,
You could try offering amonstar $140, I bought four off him together for $125 each delievered about ten months ago.
Fitting the pot is an easy mod(Ray G did a thread on it https://www.woodworkforums.com/f65/hu...el-pot-147356/ ). Depending how you plan to mount the drive you might want a remote pot anyway. But if he wont move on price and it only comes down to $9, I'm with Joe.

As far as motors go I think I'd go with a 4 pole. I'm lead to believe that the rotor and bearings in 4 pole motors are the same as in the 2 pole so you can run the 4 pole up to 2800rpm with the VSD. I dont believe you would get to 2800rpm with normal 6 pole motor but havent tried it.

Stuart

Simon

I too have been looking at the VFDs, albeit slightly larger and not for a lathe application, so I would be interested to hear people's opinions. I did note that the prime difference in price seems to relate to where they are posted from. UK, USA or Hong Kong. In some instances the same seller has the same product available through different countries and a lot is down to freight and the relative strength of the aussie dollar.

Regards
Paul

Thanks guys,

I figured the front pot to be a bonus. I will most likely be installing a remote pot and controls anyway.

Stuart, WRT the motors and No. of poles: Am I right in assuming it's all about what speed range you want. As in a 2 pole motor normally runs at 2900 rpm so you may get a range of say half that speed and up to double, so speed range 1500 - 6000 rpm (theoretically speaking although 6000 rpm may be pushing it) and say a 4 pole motor which normally runs at 1500 so you may get 750 - 3000 rpm. I understand you may get lower rpm's than these but I am lead to believe that the speed may not be usable due to lack of torque.

Am I on the money (basically) with my summary?

> I figured the front pot to be a bonus. I will most likely be installing a remote pot and controls anyway.

With most VFD make it is a bonus. But there are some VFD models, where the front pot is an optional module that must be removed, in order use an external pot. I always very highly recommend that before buying a VFD, one downloads its user manual and its installation manual. If no download is available, of if you do not like the way the VFD is programmed, forget it - there are plenty of other VFD makers. In an earlier post was the question about the brand of IGBT module. There are only a few companies capable to make these, think the very big power-semiconductor brand names like Mitsubishi, Siemens, Toshiba, Hitachi etc etc. The newest IGBT's they use exclusively in their own newest VFD'd. Only the obsolete IGBT's are supplied to other VFD makers that do not have an own semiconductor factory. Knowing this may matter if you buy for features/performance rather than price only.

WRT number of motor poles: yes, it determines the speed range that will be available, but there are a few caveats you need to be aware of:

- A low cost "V/Hz type" VFD drive with a "normal" 3 phase motor, has a constant torque characteristic from about 20Hz to 60Hz, and a constant power characteristic from 60Hz to about 100Hz (in other words, power rises linearly with rpm up to 60Hz, then remain stable and finally begins to drop off past some 80Hz, not unlike a combustion engine). It remains usable from about 12Hz to 120Hz at a greatly reduced power output. With "normal" motor I mean an easily available and affordable off the shelf standard TEFC motor, as opposed to an expensive special VFD motor that usually is only available on order.

- A "vector type" VFD drive with a "normal" 3 phase motor, has a constant torque characteristic from about 7Hz to 60Hz, and a constant power characteristic from 60Hz to about 100Hz (in other words, it behaves very much like a DC motor up to 60Hz, and like a combustion engine above 60Hz). It remains usable at greatly reduced power output from standstill to 120Hz. With "usable" I mean smoothly operating, no rough running or hunting.

- a motor of given HP needs a bigger frame and is heavier, the more pole it has. In practice, a 1HP 4-pole motor has the same frame as a 2HP 2-pole motor, and a 1HP 6-pole motor has the same frame as a 4HP 2-pole motor. This may well imit your motor choice. In some cases, you may find it better to reduce rpm by a gear or belt reduction rather than a larger motor frame - in other cases you may find it better to accept a lesser HP motor rather than go for a larger frame.

- all "normal off the shelf" 3 phase motors of a given series are made with the same rotors, regardless if the stator is 2, 4, 6 or 8 poles. And all "normal off the shelf" motors are designed for 60Hz base frequency (except very large motors).
This means that the rotors are designed and balanced for a maximum speed of 3,500rpm. There is a more or less generous safety factor added to these 3500rpm, depending on motor quality. But I would say it is pushing ones luck to go above say 4500rpm. Also, the fan attached to the other end of the rotor will become noise and take up quite a portion of the available power at those rpm. All that limits the maximum frequency, at which you can run a 2-pole motor. It will not affect motors with higher pole numbers.

- at speeds below some 25Hz, the fan of a "normal off the shelf" 3-phase motor will not produce enough airflow to keep the motor from overheating, if run continuously for long periods on a hot day. This is rather irrelevant on a manual lathe or mill unless used industrially, but it certainly matters if used say to drive a conveyor for an 8 hour nonstop shift. Such motors should be fitted with a separate and independant cooling fan. Chris

Hi Simon,
I think Chris has pretty much covered it.
So to say the same thing in a different way(I think). I wouldnt use the 2 pole as its not rated to go over 3500rpm(and would just mean I higher gear ratio to get to the speeds I think you are after). The 4 pole (in theory at least) should be happy enough running at 3000rpm(granted with not much power, but at that sort of rpm you won't be needing much). As Chris has confirmed a 6 pole is unlikely to run at high enough Hz to get it to 3000rpm.

Stuart

Hi Chris + Stuart,

yep I think a 4 pole motor would probably be a safe happy medium for my use. I have just downloaded a copy of the VFD manual form the models available on ebay. Boy! It's not simply a matter of wiring it up and turning it on!

Thing that concerns me the most (on first glance) is getting the V/F curve wrong and cooking the motor. There are so many parrameters and features on even these cheap VFD's, more than someone like me will ever need!


Some light reading for me coming up I think!

Also, I posed a question before. Does anyone know if you can run a 220V DC permanent magnet motor on a 180V DC speed controller (assuming current rating is sufficient)??

If not then I can't see myself using that DC motor I have (photo on previous post) or at least not for that application anyway.

Cheers,

Simon

Hi Simon,
I've wired up 6ish motors and havent managed to cook one yet. I just run the defaults unless I have an issue(well except that my VSD's came set to run at 400Hz, you might want to check that) . But then I generally operate in the 10Hz to 60Hz range, the low Hz for setup, I think the lowest I have machined with was 25Hz. You're going to want to push that I assume.
As far as the manual goes(and it is pretty shocking) I didnt find the Teco one much easier to read. The biggest problem with the manual is they have labels mixed up. PD048 and 049 for e.g. in one part 48=SPL 49=SPM, in another 48=SPM 49=SPL, outputs labeled as inputs, set ranges incorrect. So maybe the Teco one wasnt that bad after all and I learnt on the Teco so had more of an idea what I was doing when I got the Huanyangs. Though the Huanyangs do have many more parameters most of them we arent likely to use.

Stuart

Originally Posted by simonl

Thanks guys,

I figured the front pot to be a bonus. I will most likely be installing a remote pot and controls anyway.

Stuart, WRT the motors and No. of poles: Am I right in assuming it's all about what speed range you want. As in a 2 pole motor normally runs at 2900 rpm so you may get a range of say half that speed and up to double, so speed range 1500 - 6000 rpm (theoretically speaking although 6000 rpm may be pushing it) and say a 4 pole motor which normally runs at 1500 so you may get 750 - 3000 rpm.

I asked a relative who designs and builds small industrial motors in Europe about this a while back and he gave me an almost identical response to cba_melbourne.

dc varies the voltage for speed. A 220 motor will run just fine on 180. It may not reach rated speed. DC motors rock for torque through the entire range. Speed will vary with load with a cheap VSD but those equipped for resolver feedback can almost eliminate any drawbacks this might cause.

You guys seem all over this topic like a fat kid on a cup cake!

For ##### and giggles I may even set up a DC motor and speed controller on my drill press and a vfd + 3 phase on the mill just to have a play and compare. If I like either then I may look to convert my lathe too. If I set the lathe up on 3 phase I will hoping to be a tight #### and use the same VFD on both mill and lathe, obviously not operating at the same time though!

Thanks again!

Simon

[QUOTE=cba_melbourne;1554815 - all "normal off the shelf" 3 phase motors of a given series are made with the same rotors, regardless if the stator is 2, 4, 6 or 8 poles. And all "normal off the shelf" motors are designed for 60Hz base frequency (except very large motors).
This means that the rotors are designed and balanced for a maximum speed of 3,500rpm. There is a more or less generous safety factor added to these 3500rpm, depending on motor quality. But I would say it is pushing ones luck to go above say 4500rpm. Also, the fan attached to the other end of the rotor will become noise and take up quite a portion of the available power at those rpm. All that limits the maximum frequency, at which you can run a 2-pole motor. It will not affect motors with higher pole numbers.

- at speeds below some 25Hz, the fan of a "normal off the shelf" 3-phase motor will not produce enough airflow to keep the motor from overheating, if run continuously for long periods on a hot day. This is rather irrelevant on a manual lathe or mill unless used industrially, but it certainly matters if used say to drive a conveyor for an 8 hour nonstop shift. Such motors should be fitted with a separate and independant cooling fan. Chris[/QUOTE]

Chris

Thank you for a very informative post and in particular addressing the speed issue. I think that will have answered a great deal of concerns for a large number of people including myself.

Regards
Paul

G'Day Simon,
KB controllers seem to start at $60 - $70 on U.S. Ebay, you would have to watch the postage, the issue of running D.C. motors at below maximum voltage has been addressed above so shouldn't be a problem. A couple of other thoughts though, what max spindle speed were you thinking of running ? (possible bearing issues), given the size and possible weight of the motor, are the motor mounts on your mill up to it (the pressed metal crap on my RF31 would probably shear off in the first 10 minutes). While I have had a fair bit of experience with D.C. motors in industry I can't recall having seen one mounted vertically, I am wondering if when the brushes wear and carbon dust builds up and falls to the bottom of the motor will this cause bearing problems ? (dunno).
Regards,
Martin