Running 2 speed motor off a VFD

G'day guys, I have a 2 speed 3 phase motor, currently connected WYE that I want to run off 230V single phase as I do all my machines. However I haven't ever use a VFD with a 2 speed motor and wonder what the connection options are? Obviously I know it's possible to reduce the speed using the VFD, but wonder if there's any benefit, or even if it's possible, to preserve the inherent 2 speed potential of the motor?

Note this is for connection to an AUSTRALIAN 230V source (as per UK and most of world), NOT North American.

Pete

I don't think that works. If it does, I'd like to know (and will add an VFD to my band saw).

Reason:
A two-speed motor usually (or always????) is a Dahlander motor. It switches the coils from parallel to serial and from (double-)wye to delta. So the VFD will see different inductions and resistances. That will confuse him.
At least that's my thinking. And I'll stand corrected. Maybe some VFDs do accept that.


Nick

Pete F said:

G'day guys, I have a 2 speed 3 phase motor, currently connected WYE that I want to run off 230V single phase as I do all my machines. However I haven't ever use a VFD with a 2 speed motor and wonder what the connection options are? Obviously I know it's possible to reduce the speed using the VFD, but wonder if there's any benefit, or even if it's possible, to preserve the inherent 2 speed potential of the motor?

Note this is for connection to an AUSTRALIAN 230V source (as per UK and most of world), NOT North American.

Pete

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Really, really bad idea. I think you should let me take that motor off of your hands next time I'm in Sydney and I'll throw in $50 to put towards a nice new single phase motor for you. Or a single speed 3 phase with VFD. That's a lot simpler.

Trust me, that Aciera will work a lot better with a new motor....

PDW

PDW said:

Really, really bad idea. I think you should let me take that motor off of your hands next time I'm in Sydney and I'll throw in $50 to put towards a nice new single phase motor for you. Or a single speed 3 phase with VFD. That's a lot simpler.

Trust me, that Aciera will work a lot better with a new motor....

PDW

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Hmmm, let me think about that for a moment Peter ...





Nick, yeah I'm not sure how it's actually connected, and as you can imagine it's tucked in to the guts of the machine. I'll pull it out and have a better look at it as the name plate threw me a little, it wasn't what I was expecting.

I could just run it on its high speed windings and use a switch to program the VFD to the 2 different speeds, but I don't know much about 2 speed motors at all and don't know if there's some advantage is using all the windings.

Edit: BTW if you want one of these motors I know of a large and wise man who has (had?) one.

Pete -
I have recently gone through all this but for a three speed motor. It really depends on what connections your motor provides as to whether it will be sensible to try and use the two speed motor with a VFD.

The most critical factor is that you want to operate on 230V single phase VFD input (just the same as UK). The problem with this is that it requires you to use delta connection for your motor, on either or both windings. You will need to check whether this is possible with your motor. If it is, then you may be able to use the multi-motor parameters that are available with some VFDs to set up for the two windings. You would then need some way of switching the windings from one speed to another. This would be between the VFD and the motor. This is a really bad (VFD goes bang) thing to do unless you have some kind of interlock that powers down the VFD AND stops the motor before the switching takes place. The winding change over switch would also need to supply the signal that tells the VFD that the second set of windings are in use. This is not at all easy to do in a fail-safe fashion. I am told that there are VFDs that handle all of this for you, but I have never found one that can do it with a delta connected motor. The reason that you need to have the motor stopped as well as the VFD powered down is that on many machines (such as a lathe) there is significant inertia in the drive from the motor to the spindle. If you just cut the VFD power and then switch as the motor runs down, it will be generating current which the VFD would normally handle through a braking resistor or other circuit. Interrupting this is not healthy for the VFD.

If you cannot connect in this way, but you can still connect one set of windings in delta, then you should be able to use your VFD with the motor. You will have a hard choice to make in that case because if you choose the high speed windings you will obviously get your maximum speed, but you will probably not be happy with using the VFD to slow it down for the lower speeds. The opposite argument applies if you choose the low speed windings.

You can in theory get around the 230V delta connection problem by using a 230V in 415V out VFD. I am aware of one supplier in UK who modifies standard VFDs to do this. In that case you are released from the requirement to use a delta connection and things should be easier to sort out, but you still need to set up a fool-proof way of switching windings without destroying your (very expensive in this case) VFD.

In my case the three-speed motor was on a lathe where the whole idea is to be able to change speeds quickly on the fly. Your application may be different of course, but I decided in the end that the compromises that were inherent in using the original three speed motor with a VFD were too great and I opted to go with an up-sized single speed dual voltage motor instead.

Pete F said:

Hmmm, let me think about that for a moment Peter ...





Edit: BTW if you want one of these motors I know of a large and wise man who has (had?) one.

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Umm, actually - he doesn't :-) But I know who does have it..... won't say what it changed ownership for, though.

OK, $100 for yours and a free set of Big W steak knives.

Incidentally if these can be run off of a VFD I know at least one other person who'd like to know the details as well. Doesn't even have to be a single phase VFD, some people have 3 phase......

PDW

Thanks Bill, as PDW alluded to above, it's on an Aciera mill. I'm not overly concerned about any interlock as I am the only person to use the machine, and know not to disconnect a motor from a VFD with either active. I don't have the same inertia problems to contend with as a lathe, which would be a bit painful, and always possible that it's switched when still spinning.

I have considered the possibility that one of the star points may be internal to the motor, at this stage until I get it out and look more carefully at it I won't know for sure. I've pulled numerous star points out from other motors and normally they're no biggie, just find them and rewire, but this one could be a little trickier.

Pete

PDW said:

Umm, actually - he doesn't :-) But I know who does have it..... won't say what it changed ownership for, though.

OK, $100 for yours and a free set of Big W steak knives.

Incidentally if these can be run off of a VFD I know at least one other person who'd like to know the details as well. Doesn't even have to be a single phase VFD, some people have 3 phase......

PDW

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Oh you're a lucky ... ooops I mean HE'S a lucky guy

It could definitely be run off a VFD if I was prepared to wire it up to just one set of windings, and I'm pretty sure it's a no brainer if using the high speed ones, but as Bill suggested, therein lies the problem, which windings to use if it's decided to use just one set. In this case there's a big difference in motor speeds, more than I expected.

Pete -

Doing this on a mill is slightly easier because the drive line inertia is usually limited. You don't say which Aciera you have, but if like (say) an F3 there should not be a lot of inertia and you probably can get away without a brake resistor - making the switch-over a bit easier and quicker. It might be worth looking at what people have done to add VFDs to Bridgeports with a two speed motor, although I have a nagging feeling that your motor may be different.

Pete F said:

Oh you're a lucky ... ooops I mean HE'S a lucky guy

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Yeah I think I was robbed....

Pete F said:

It could definitely be run off a VFD if I was prepared to wire it up to just one set of windings, and I'm pretty sure it's a no brainer if using the high speed ones, but as Bill suggested, therein lies the problem, which windings to use if it's decided to use just one set. In this case there's a big difference in motor speeds, more than I expected.

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Must say I'm surprised as well. I was expecting 1440/2880. Doesn't matter to me, I planned on fitting it to Natasha my Romanian mill in place of the single speed with VFD motor that the previous owner upgraded it to because he didn't have 3 phase. That was fine as far as it went but *he threw out the 2 speed 3 phase motor!!!!!!*

Sob. I would have paid more for the machine if only he'd kept that motor. Taking it off, sure, but throwing it in the trash? Aaaaargh.

So when I actually collect this motor from the large & wise gentleman (via his trusty Melbourne agent) - hopefully next month - I'll look at converting the mill back again, assuming the speed ranges will work out OK. Got some doubts now. If not, no dramas, I can see my vertical slotter getting a retrofit as the 2 speed motor would be perfect there on its lower speed, especially hooked to a VFD.

VFD's being relatively dirt cheap nowadays, what about hooking 2 of them up, 1 to each set of windings, and a switch before them to selectively power up only 1 at a time? Even if that won't work for you with single phase, would it conceptually at least work for me?

PDW

Yep, it's an F3.

Ok I just took a look through the wiring diagram, I'm not sure if it's the one for my machine, but suspect mine would be similar. It appears as if the two sets of windings are in fact completely independent WYE windings, is that possible? I'll try to figure out a way to post the relevant pdf page as an image and see what others think, but I'll need to do that tomorrow as my eyes are rolling around in my head like a mad cow at the moment and it's time for bed.

Pete

Edit: funny you should mention using 2 VFDs as I actually typed that out and deleted it. But yes it's definitely an option. I use Sew Eurodrive VFDs and they're unfortunately not cheap, but excellent quality, so it would be an expensive solution.

billmac said:

Pete -

Doing this on a mill is slightly easier because the drive line inertia is usually limited. You don't say which Aciera you have, but if like (say) an F3 there should not be a lot of inertia and you probably can get away without a brake resistor - making the switch-over a bit easier and quicker. It might be worth looking at what people have done to add VFDs to Bridgeports with a two speed motor, although I have a nagging feeling that your motor may be different.

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Funnily enough PeteF has an F3....

As for a B/port, I have one of those but as I have 415V 3 phase, never thought about putting a VFD on it. Actually now I stop & think, my motor is only single speed anyway, it has back gearing to get the low speeds. Now an Arboga drill has a 2 speed 3 phase motor.

PDW

Ok I can't get an image of the wiring diagram up tonight, but instead here's a link to the manuals
https://skydrive.live.com/?cid=547fe296ecfd561f&id=547FE296ECFD561F!2918

I think if you click on the link "Aciera F3 Schémas électriques - 1972" [without the quotes] I'm pretty sure that's how mine will be wired.

Pete F said:

Ok I just took a look through the wiring diagram, I'm not sure if it's the one for my machine, but suspect mine would be similar. It appears as if the two sets of windings are in fact completely independent WYE windings, is that possible?

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Yes that's possible, in which case you will need to find two entirely distinct star points in the windings and of course work out what belongs to what - but that should not be difficult.

See this for a collection of the possible ways to connect a two speed motor, together with the resulting properties. A three speed gets much more complicated ...

Google Image Result for http://www.industrial-electronics.com/image/12-30.jpg

Pete F said:

G'day guys, I have a 2 speed 3 phase motor, currently connected WYE that I want to run off 230V single phase as I do all my machines. However I haven't ever use a VFD with a 2 speed motor and wonder what the connection options are? Obviously I know it's possible to reduce the speed using the VFD, but wonder if there's any benefit, or even if it's possible, to preserve the inherent 2 speed potential of the motor?

Note this is for connection to an AUSTRALIAN 230V source (as per UK and most of world), NOT North American.

Pete

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Note that your motor is constant torque, which means the power (KW or HP) is directly proportional to the RPM. And that is exactly how a VFD behaves at frequencies below the nameplate 50 HZ. So, the VFD will make 1.5 KW at 50 HZ and 1/3 of 1.5 KW at 1/3 of 50 HZ at 1/3 of 2850 PRM. And you get the same effect if you use the low speed windings at 50 HZ. The only advantage I can see to using the low speed windings is avoiding cogging, and only a test run will tell if that is a problem.

If you run the VFD at frequencies over 50 HZ, the motor will have constant power and declining torque. That is why I would not try running only the low speed windings and running the frequency up to 150 HZ. You would then have only .5 KW at 150 HZ and 2850 RPM.

Larry

My Emco V13 has a 415vAC Elin LCP610-L01 motor that is of the Dahlander Type (Delta/Wye Wye).

These motors are single voltage 2 pole - 4 Pole switching motors to give 1420 and 2860 rpm.


The wiring connections on the Elin look like a basic 1u-1v-1w....2u-2v-2w connection block (as seen in dual voltage ACIMs) , as the extra connections are internal.

I have one of the Direct Drives 230VAC in -> 415vAC out Teco VFDs controlling the motor and the brake...and it has worked well for 6yrs so far.

I run it in 2 pole configuration which allows full speed but at a slightly reduced torque ,but it runs fine on the 4 pole higher torque mode at the reduced speed. (The lower torque for less poles issue is a basic induction motor issue).

Rob

Ps.

The Direct Drives units are normal 415vAC In -> 415vAC out drives that they add a couple of wire jumpers to..to make the mid point of the "stacked" input capacitor connections act as a Bridged Delon voltage doubler.

I know that a number of drive manufacturers offer dual motor maps or the ability to add programming logic to the drive to accommodate same.

I once set up 4 such 50hp Baldor Vector drives in the hull of a barge running 24" augers that would push wheat toward the center unloading well. The augers start out in 8 pole operation for the much needed torque after a long river ride with grain settled and packed around the screws.

Feed the well where a bucket conveyor lifted grain to the silos, we hade a current sensor on the lift conveyor and fed the well with the screws such that the conveyor motor operated at max HP.

Once the screws were operating at max 8 pole Hp, we would switch windings (using an interlocked reversing motor starter) and the drive automatically switched motor maps) and off the the races we went.

The barge unloading system monitored an inclinometer and we adjusted screw speed to keep the unloading conveyor maxed out while keeping the barge level and correcting for any list.

These were two speed constant HP motors that ran about a 20:1 speed range

Groan, well I pulled the motor out this afternoon and as I feared, the star point(s) wasn't easy to find. I just need the one for the high speed windings, but it's a real rat's nest in this motor and it's quite heavily varnished. I think I'll cut my losses and take it to a motor rewinder and let him do the digging. I started but it wasn't coming up easily, so on a motor like this that I don't want to trash I'd prefer somebody who's experienced with them to do it. It should only cost 60 bucks or so, and not worth the risk at this stage.

Here are a couple of pictures of the motor and how it's connected. I didn't take any more photos of the work in progress as I needed to call it a night.

Pete F said:

Groan, well I pulled the motor out this afternoon and as I feared, the star point(s) wasn't easy to find. I just need the one for the high speed windings, but it's a real rat's nest in this motor and it's quite heavily varnished. I think I'll cut my losses and take it to a motor rewinder and let him do the digging. I started but it wasn't coming up easily, so on a motor like this that I don't want to trash I'd prefer somebody who's experienced with them to do it. It should only cost 60 bucks or so, and not worth the risk at this stage.

Here are a couple of pictures of the motor and how it's connected. I didn't take any more photos of the work in progress as I needed to call it a night.

View attachment 88848View attachment 88849

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How about $100, 2 sets of steak knives, chocolate for your wife and some suitable (my definition) toys for the kids?

PDW

PDW said:

How about $100, 2 sets of steak knives, chocolate for your wife and some suitable (my definition) toys for the kids?

PDW

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Come on, It's French- its not worth a bean....
I have a proper english motor of the same specs here, recently rewound, its so heavy i can barely lift it. Did I mention the bearings are stuffed, and well, being english and of a particular age, foresaid bearings have dimensions which DO NOT CONFORM to those accepted by the rest of the world for the last 100 years and are consequently priced beyond reason.

I bet it would run all day, silently, without even getting warm.......
D