3 HP conversion finished

[dinges]

Early in 2006 I started a conversion project of a 3hp induction motor. It got finished this week. See these links for some more info:

http://www.fieldlines.com/story/2006/6/15/19126/8190

http://www.fieldlines.com/story/2006/6/18/11456/6477

The specifications of the motor:

manufacturer 'EMF Dordt', Holland.

type 292 U  30/4

3hp; 2.2kW

n=1415RPM

V 220VAC (delta) 380VAC (star)

I 9.0A (delta) 5.2A (star)

3 phase

cos-phi = 0.80

resistance per phase: 2.70 ohm

weight 35 kg

The original rotor was taken out and replaced by a new rotor. The new rotor is made of steel with an alumium cage. See this link for the CAD drawing of the final design:

http://www.anotherpower.com/gallery/dinges/3pk_rotor_ombouw_edit?full=1

The conversion itself consists of 40 magnets N42, 20x10mm. This gives a total magnetic volume of 7.6 cubic inch (which, according to 'Zubbly's rule' should yield about 1100W). The stator has 36 slots, so slot width is 10 degrees. The magnets are mounted 'Zubbly style', that is in a helix, where each magnet is off by 2 degrees. This is done to prevent cogging. A lot of thought went into the decogging part of this conversion. See these two links for a complete read-up of the idea behind it: http://www.fieldlines.com/story/2006/6/15/19126/8190

http://www.fieldlines.com/story/2006/6/18/11456/6477

Many more pictures of it are available in my IRC gallery (http://www.anotherpower.com/gallery/dinges?page=8 and http://www.anotherpower.com/gallery/3HP-induction-conversion)

The results:

A motorconversion that is absolutely cogless. Not even the slightest hint of cogging is present anymore.

The motor was mounted on a lathe to test the voltage output (volts per phase, VAC):

RPM        volts (VAC, per phase)

110.         9.5VAC
     
145.         13.0VAC
     
190.         17.7VAC
     
600.         60.0VAC
     
783.         78.0VAC
     
     

(The RPMs were checked with a RPM counter)

So, we need about 10RPM/V. By changing to star or delta, we can influence final voltage a bit more.

When shorted, the generator becomes almost impossible to turn by hand. Each phase has a resistance of 2.70 ohm (measured with milli-ohm meter).

No measured results with respect to stator (iron) and bearing losses are available

yet. They are not insignificant though.

I have not an idea yet of what kind of prop to mount to it. Probably about 10-12 ft

diameter, but first I need to brush up my knowledge of designing and building blades.

Yet to do:

Build a yawing mechanism, build a hub, make a prop, get a tower and mount it all together...

Finally, some thanks are due. First of all to my friends Peet and Nobby, who helped to machine the rotor. Bedankt! Secondly to Zubbly and Wdyasq/RonB, whose critical remarks and opinions were appreciated. Finally to the people on otherpower.irc and the knowledgeable people on this board. Thanks.

Peter.

[willib]

scooped again peter?

your Rpm readings are unreadable? its best to insert a space before all leading numbers..

very cool looking machine , no cogg huh? nice!

what size magnets are they

[dinges]

Nope, not Scooped, not this time. RPM readings & voltages are correct.

The conversion itself consists of 40 magnets N42, 20x10mm. That's about 3/4" x 3/8"  

[wdyasq]

Looks good in my browsers, I use four different ones.

Ron

[TomW]

Ditto, perfectly aligned and readable in FF 2.0.

And, Dinges, glad we could encourage you to do such a nice job even tho it took being mean and vengeful to accomplish it.

I told you wasting time on IRC would lead to trouble.....

Cheers.

TomW

[Countryboy]

Good job Peter!

How many wires did you pull out of the genny?  Did you just break the internal star connection, or did you use a different method for pulling extra lead wires out?

If you had this to do over, have you found anything you would have done differently to improve the conversion?

You forgot to repaint the case.  People often judge quality of workmanship by what they can see - and the paintjob is the easiest to see.  You have a beautiful new rotor, in a paint chipped case.  

If you intend to repaint now, rather than using masking tape to protect certain areas, it may be easier to cover spots with Vaseline.  Paint, and then after the paint has dried, the paint on the Vaseline covered areas will peel away.  (I know people who would smear Vaseline on the windows and trim of their car when they were repainting it.  It is a quick and easy way to mask.)

[dinges]

Hello Countryboy,

Thanks for the compliment.

None of the wires were pulled out. For all 3 phases, both connections (start & end) are available in the connection box, 6 in total. In the box you can set jumpers for star or delta. Unlike Zubbly does there's no way of making any extra connections available, as far as I know. I've often tried to understand how Zubbly did it, until I realized European motors are built/wired differently from the ones in North-America.

"If you had this to do over, have you found anything you would have done differently to improve the conversion?"

Very good question. Actually, there's one mistake I've made; my magnets are a little too deep in the the steel rotor (about 1/3 their height). This is a design error, caused by me switching magnet size during the design process (from 15x8mm to 20x10mm). I neglected to correct for this. My magnets could have been 2-3 mm higher out from the steel rotor (i.e., steel rotor should have been 5-6mm smaller in diameter, and aluminium cagering a bit thicker, to arrive at the same outside diameter of 88mm). I'm losing some magnetic flux because of this error.

That's about the only thing I should have done differently with this conversion.

You're not the first one to make remarks about the paint job

I wanted to wait with painting till I was sure the conversion worked. It will be re-painted, with some 2-component lacquer. It just wasn't very high on my priority list, but needs to be done. I normally try to look beyond the surface at the essentials. Beauty on the outside says nothing about the beauty (craftmanship & effort) on the inside. Nevertheless, I'll repaint, if just for the functional reason of corrosion protection

[Flux]

I had that trouble with my earlier version of IE. I found in the end you could correct it by reducing print size. Now Bill Gates has sent me the latest version of IE it doesn't seem to do this.

I thought for a while it was Scoop and yes adding a space does prevent it on the old browser.

Flux

[Flux]

Interesting results. At 1500 rpm you would get 150v ac.

I assume you are star connected so you have well below the 380v so you have quite low flux density in the gap.

I am not surprised that cogging and iron loss are small.

It would be interesting to do a load run into a 24 v battery to see what signs of reactance limiting there is. This will determine the final output you could get out of it.

If those voltages are star, it looks as though it may take an 8ft prop in delta of perhaps 10 ft with star /delta switching as long as the reactance doesn't have too much effect. The 2.7 ohms value again I hope is star so in delta it will be nearer an effective resistance of about 1 ohm.

Not very good efficiency but good cooling so the losses are not such a problem.

Does your lathe have the power to do this load test, this is quite interesting.

Flux

[ghurd]

It looks great!

What are the main wiring differences between this and North American motors?

G-

[Flux]

Europe and UK uses a 380/415 volt 3 phase distribution system. Single phase is taken from line to neutral to give a nominal 230v with the neutral earthed.

Motors only need to work on 415v 3 phase but normally they are arranged for star delta so they can be used on 230v 3 phase for some inverter drives and export.

Voltage varies a bit between countries but I think they are trying to settle for about 230/415.  There is still some 250/440 in uk but gradually it is dropping and probably it has officially gone. I suspect others are raising their 380 to something a bit higher. Frequency is 50HZ.

Motors normally come with 6 leads for star delta.

Flux

[dinges]

Hello Flux,

All the measured values that were given are for -one- phase only, i.e. not connected star and not connected delta. At the moment, the motor is wired in star.

At 1500 RPM I would get 150VAC for that one phase, which would mean in star, about 150VAC * 1.73 = 260VAC.

Cogging is absolutely zero, but iron losses are definitely there, -not- negligeable. Haven't made measurements of the stator(iron) losses yet, but I will do, it is very relevant information. I don't think my flux is as low as you suggest though. When I short the outputs, the thing becomes practically impossible to turn. Only with a major effort can one still rotate the axle.

In star the internal resistance of the genny will be 2.7 ohm * 1.73 = 4.67 ohm; in delta it will be 1.56 ohm. I'm curious too as to any reactance limiting; whether it will be a more stringent limit than e.g. coil resistance, in my case.

[Flux]

Thanks for clarifying Peter. If that was one phase then it does indicate a higher flux, unfortunately it also means a rather inconvenient voltage and high resistance unless you can run it at 48V. Actually the star resistance will be twice phase not 1.7 times.

This is more or less inevitable if you start with a 380v motor.

Unless you can use it at at least 48v I think it will reactance limit quite badly.

You may have to break the connection between pole groups and parallel, with some risk of circulating currents or make it 2 independent windings with separate rectifiers in parallel.

Yes it would be nice to know the iron loss.

Flux

[Darren73]

Hi Peter,

Congratulations on your achievements, one quick question, the phase resistance you quote as 2.7 ohms star as 4.67 ohms and delta as 1.56 ohms, the star resistance would be 5.6 ohms and delta resistance would be 1.8 ohms between any 2 legs by ohms law.

kind regards

Darren

[Countryboy]

IIRC, it is generally considered to be ok to have magnets sitting in pockets less than half their height.  Flux loss will be minimum as long as the pockets are less than half the height.  It is when you get into deep pockets that you really get into trouble with high flux losses.  Since your magnets are only 1/3 in the pocket, I wouldn't lose any sleep over it if I were you.

I too believe substance is more important than style.  Performance is what matters, and looks don't contribute anything to performance.

I did think of another question for you.  What is your airgap between the magnets and the stator laminations?  What is the size difference between the outside diameter of the rotor, and the inside diameter of the stator laminations?

[dinges]

I understood magnets shouldn't be deeper in the steel core than about 1/4 their height. But, generally, the less deep the better. I don't think it's a big issue, just that it's something I'd rather have done differently with this genny. Lesson learned.

Gap between the aluminium ring and stator core is about 1mm (2mm over diameter), but the magnets are slightly below the outside of the aluminium ring. I guess about 2.5mm airgap from magnet to stator (in the middle of each magnet). I could have gotten 1mm less, and it will be slightly less in a new, bigger genny. However, I will keep the magnets below the outside of the aluminium ring, so as not to damage the magnet-coating when inserting (or removing) the rotor in the stator.

I.D. of the stator is 90mm

O.D. of the aluminium rotor is 88mm

Magnets are about 1.5 mm below the outside alu ring (in the middle of a magnet).

So, about 2.5mm airgap between magnet & stator.

[SparWeb]

Peter,

Congratulations!  I've followed your work with great interest.  I will concede that your genny probably cogs less than mine, and since you put so much effort into avoiding that, it must be very satisfying.

I can't help noticing the similarities with our results:

Each phase of your genny has almost exactly the same resistance as mine, too, so 17 gauge (1.1 mm dia), right?  

Your open-circuit voltage figures are almost exactly equal, so I expect that if you try a battery charging test on a lathe you will also have the same results.

My conversion-genny is gathering a thick covering of sawdust (along with everything else in my garage) as I am currently cutting blades.  I look forward to hearing more news in the new year.

Cheers!

[dinges]

Hello Steven,

Yes, the fact that it doesn't cog at all I'm most happy with. It means that for the next conversion, 10hp or so one, I don't run the risk of wasting lots of time, effort, money & magnets on something that won't work (very well). My hands are itching to start working on a really big conversion (even if it may not fly within the first 5 years).

So, it seems we have 3 methods for a non-cogging conversion:

1. Zubbly's skewing the stator (haven't tried this method yet)
   
2. Zubbly's helix-rotor (which is guaranteed cogless, if designed right)
   
3. JacquesM's method of offsetting the poles on the rotor
   
   

IMHO, the cogging issue is no excuse for not building a conversion. It can be done, as has been proven time & again by Zubbly & others. Always nice to be able to confirm myself they were right

I'm afraid this conversion too will be gathering dust for a while, as the rest of the project gets worked on. Most likely, I will first be finishing a small 130W conversion, before starting on blades for this 3hp one.

Now, if anyone has a 10hp motor they're willing to get rid of...