Hi every 1, planning a huuuuge motor conversion... Guidance sought.

[therapy]

Hey all, very nice forum you have here, I have had a look at some of the alternators guys have built up and I must say it's quite impressive.
I'm not sure if this is the right spot for this, so perhaps a mod could move it to the right spot if need be.

So, I am down under, in good ol' 'Stralia, I'm a qualified electrician, and worked as a mechanic before that.
What brings me here is my wish to convert a massive 3 phase, 240 / 415v 57 horsepower motor into a reasonably sized generator.

Obviously, I could just hook a diesel motor up, drive it a bit over synchronous speed, and it would generate, but this is a half assed attempt, and a motor of this size should make a powerful genny if done right.

I'll get some pics up in the coming days. As I have never done a conversion before, I would appreciate your input.
This motor is to be driven by a 100 odd horse power diesel motor, not a wind turbine. I plan on using original stator windings if I can, and just chopping up the rotor and adding the right magnets. This is the bit where I need help.

Thanks in advance.

[Flux]

I have no idea what you are intending to use this for but certainly it can be done. There will be snags and as long as you can live with them you may be on a winner.

If you require a tight control of voltage or frequency there are some big issues. If it is stand alone your load requirements will decide if it is possible or not. If you intend to feed the grid then you have other issues to deal with.

It won't be a cheap project and it could be rather tricky dealing with the size and quantity of magnet needed, you will be dealing with forces needing careful management so there are safety issues to consider.

This will be more expensive than buying a commercial alternator so I have no idea why you would want to do this but as you have not yet presented any details it is too early to comment.

I will follow progress and may or may not wish to comment further.

Flux

[therapy]

Thanks for the comments, a commecially made generator of this size would nearly be 20 grand here. It will not be feeding the grid in any way. The reason I plan on doing it is the fact already have the motor and the diesel motor to drive it. As I mentioned, I'm a sparky by trade, so well aware of the dangers.

This is a 240/415 alternator project

[wdyasq]

You would be well advised to look up all of the posts by "Zubbly". He is no longer with us but was a rebuilder of electric motors and took 'conversions' to a high level.

Ron

[therapy]

Yes he seems to have quite a name for himself, have been reading  a lot of his stuff. I'll try for pics this afternoon.

[SparWeb]

I've done a few of those conversions, but nowhere CLOSE to the size you are proposing.
I took lots of pictures as I went so maybe it will help.
You will have many concerns that I didn't even have to consider, in the scale of your project.
What's the design speed of the generator?  What system voltage do you intend to power?

[Flux]

Cost is something that varies wildly with area and local availability so the cost issue i mentioned may not apply but unless you have a very cheap source of neo I can't see how this option is cheap.

I would have thought you could build a wound rotor field magnet system for a fraction of the cost of the neos but again that could be influenced by local factors.

If it is stand alone you should be in with a good chance. As long as frequency doesn't have to be exact I suspect such a large neo magnet alternator will have good enough regulation for normal use and as its voltage varies directly with speed you could adapt the engine governor to keep volts within limits. if you have to maintain fairly close frequency then you will struggle to deal with volts if they are critical, especially using an original winding.

The safety issues I was concerned about were not electrical, they were the problems of handling very large neo magnets and threading a large pm rotor into a stator. Much larger( orders of magnitude) pm alternators have been built successfully but you have to think one step ahead. If something is overlooked it can be rather serious.

What Sparweb and Zubbly have done are likely to be your safest approach, you won't get nearly as much neo in there as with special curved magnets and the output and regulation will be worse but it may prove safer to do it with lots of small magnets.

Flux

[therapy]

Ok, Sparweb, I think its designed to be a 1470 rpm motor, so a 4 pole.
It will be a 3 phase, 240 volt / 415 volt 50 hz AC


Flux, explain to me a bit more the idea you mentioned regarding wound rotors. Sounds like it might be a better option?
The genny is completely stand alone, and will be more than likely used for remote welding, grinding, lighting. Running compressor motors, and other workshop tools.

I would like to be able to run more delicate electronics from it, like computers, and tv's if we ever need to.
What sort of kva should I be able to pull on standard stator windings? Any guesses?

My source for magnet material was going to be good old ebay, unless you have a source? As I'm a noob to this, I'm not aware of where to get the goods at the good price.

Thanks again.

[ghurd]

I can not imagine how great the magnetic force would be for assembly.

57HP is 19 times 'bigger' than 3HP.
Here is Zubbly's recommendation for a 3HP,
http://fieldlines.com/board/index.php/topic,127986.msg822859.html#msg822859

That is just to get the thing back inside the motor.
Once it is in there, it will be 'stuck' to one side.  Somehow, the rotor will need held in the center accurately enough, and long enough, to get the end cap back on.  Doing it safely (for man and neo) is a 2 man job even with a 1HP motor!


For TV's etc, it would be simpler to use batteries and an inverter.
Why run a >100HP motor at X RPM to power a 100W TV, 100W computer, and 50W of CFLs?
G-

[SparWeb]

Going back to what you wrote in your original post, about hooking it up to the diesel engine and running a bit over synchronous speed...

Why not try it?  It sounds like you are planning on using that set-up anyway, conversion or no, so why not start with that?
You get the platform built, engine systems hooked up, a bit of gearing installed, and then there's the wiring, electrical boxes, over-current protection, perhaps battery system and inverter, and don't forget the diesel engine speed governor to build/buy/fix.  In the big picture, the conversion of the motor is just one piece of a bigger puzzle...  and you don't need to do the motor PM conversion to accomplish 95% of the project.

IMHO.

Not trying to be negative.  Just trying to put it in perspective.  I built my wind turbine in one year, in little spurts of activity probably amounting to just a few months.  I've spent the 5 years afterward fiddling with the rest of the system!

Somehow try to find the engine project that was done by RossW (a moderator here) because firstly it's a lot more like your project than "just a PM motor conversion" and secondly he's somewhere in AUS himself.  Potentially you can go bug him in person (sorry Ross!) 

[Flux]

I don't know how to post pictures here and I couldn't find a sensible picture anywhere of a conventional wound salient pole rotor for an alternator.

You won't be able to produce a slotted wound rotor as from the early wound rotor induction motors but you should be able to build a salient pole rotor with 4 poles and pole caps to keep the 4 field coils on.This construction is typical of most standard alternators. The field coils need feeding from slip rings. Ideally the thing needs an AVR to feed the field to regulate the voltage and I can see that being a big issue for you. It would work with a fixed field supply which you could adjust manually with a rheostat or variac.

Although it will work as a capacitor excited induction generator in its present form the size makes the exciting capacitors virtually impractical. It will not self excite at any speed without magnetising current from a leading powerfactor load or from grid excitation which you don't have. If you are an expert on inverter technology you could in theory get the leading power factor from a force commutated rectifier. If you need exact frequency you need to drive it above sync speed but it will run as an induction generator at any speed near nominal with suitable capacitors

Flux

[therapy]

For TV's etc, it would be simpler to use batteries and an inverter.
Why run a >100HP motor at X RPM to power a 100W TV, 100W computer, and 50W of CFLs?
G-

Yes I agree, but an inverter for welding use, would be to say the least, very expensive.

[therapy]

Going back to what you wrote in your original post, about hooking it up to the diesel engine and running a bit over synchronous speed...

Why not try it?  It sounds like you are planning on using that set-up anyway, conversion or no, so why not start with that?
You get the platform built, engine systems hooked up, a bit of gearing installed, and then there's the wiring, electrical boxes, over-current protection, perhaps battery system and inverter, and don't forget the diesel engine speed governor to build/buy/fix.  In the big picture, the conversion of the motor is just one piece of a bigger puzzle...  and you don't need to do the motor PM conversion to accomplish 95% of the project.

IMHO.

Not trying to be negative.  Just trying to put it in perspective.  I built my wind turbine in one year, in little spurts of activity probably amounting to just a few months.  I've spent the 5 years afterward fiddling with the rest of the system!

Somehow try to find the engine project that was done by RossW (a moderator here) because firstly it's a lot more like your project than "just a PM motor conversion" and secondly he's somewhere in AUS himself.  Potentially you can go bug him in person (sorry Ross!) 

Yeah, none of that is the hard part for me, I could probably knock up a RHS frame and get the motors mounted inside a weekend.
The diesel motor controls may be a bit of a hassle but I'll get around it.

As for overcurrent protection, and what not, I am an electrician and I deal with much larger generating plants than this on a daily basis. All I really want help with is the alternator conversion itself.

I may take your advice and just run it with the original rotor and see what I get.

I have a 3 phase dummy load at work that goes from a few kilowatts  to about 400 - 500, at varying power factors down to .6 I think.

I might get it all together and load it up on the stock rotor and see what happens.

[SparWeb]

I may take your advice and just run it with the original rotor and see what I get....
I might get it all together and load it up on the stock rotor and see what happens.
I have a 3 phase dummy load at work that goes from a few kilowatts  to about 400 - 500, at varying power factors down to .6 I think.

Now THAT sounds like fun already!

All I really want help with is the alternator conversion itself.

True enough.  I wish I had relevant experience to share with you.  I don't think that anything I've done should "scale up" to your machine's level.
On the off chance you haven't already gone to look, I've published what I can at www.sparweb.ca .  It's all pretty modest compared to what you propose to do.
It sounds like this should go the other way:  you'll be able to teach me a lot if you decide to go ahead with that conversion.
Numerous other members of this forum would be interested, too.

[Flux]

"I may take your advice and just run it with the original rotor and see what I get.

I have a 3 phase dummy load at work that goes from a few kilowatts  to about 400 - 500, at varying power factors down to .6 I think.

I might get it all together and load it up on the stock rotor and see what happens."

Unless your dummy load can produce leading power factor your motor won't excite. If your load can go to leading pf it will excite and you can load it and change the pf to see how it behaves.

You have to supply the stator magnetising current which is at lagging pf. Normally with induction generators the magnetising current is supplied by the line it is connected to but for stand alone you need capacitors across the terminals. It is an unstable situation and the capacitance has always to be above a minimum to make it self excite. The more load you apply the more capacitance you need.

If you run with the optimum capacitance for full load you will saturate the core and have very high output volts  and heating on light load.

You need something similar to a hydro controller that shares the load between what you use and a dump and that is not fuel efficient for a diesel drive.

If you can manage with only a small range of loads you can choose compromise values of capacitance that will work and control the volts with the speed but at that power level you are looking at some serious capacitors.

I believe you can excite it with a pilot 3 phase pm alternator of fairly low power just to supply the magnetising current but it will have to be the frequency determining component and you will have to get the induction machine at a slip speed above that to suit the load, an interesting challenge but a major project.

Flux

[therapy]

Hi Again everyone, I busted my leg at work, so now I have all the time in the world to make stuff in the shed...

Is there any golden rule on the amount of magnets you can put on the rotor? Surely this is a finely calculated amount?

Cheers

[SparWeb]

Hi Again everyone, I busted my leg at work, so now I have all the time in the world to make stuff in the shed...

Is there any golden rule on the amount of magnets you can put on the rotor? Surely this is a finely calculated amount?

Cheers

How about "Lots is good, more is better, and too much is just enough".

You ought to look up the costs before getting too far down the road designing anything.  This could run in the thousands of dollars.

You can buy a lot of used stuff for that price.

[TheEquineFencer]

I have a place I can get 120/240 60HZ 1PH 24-25 KW generator ends for around $1000.00 USD. I do not like the OEM voltage regulation, but that can be changed to a self exciting regulator. The way they come from the OEM, it's hard starting a big motor. I also have a source for engine governor controls for around $400.00 USD plus shipping that will hold the engine speed to a preset level with a varying load. It includes the Governor control, mag pick up and actuator and linkage. I'm in the process of building a generator for myself with an Isuzu 115 HP Diesel with a 24KW 120/240 end. If you want the governor controls I can get a kit for you, I'm not sure what the shipping and import charges are for this from the USA.

[Ungrounded Lightning Rod]

Hi Again everyone, I busted my leg at work, so now I have all the time in the world to make stuff in the shed...

Is there any golden rule on the amount of magnets you can put on the rotor? Surely this is a finely calculated amount?

Sorry to hear about the leg.  (My left little finger sympathizes.)

You want enough magnets to just saturate the cores.  Anything more is wasted.  Anything much less and your output voltage will be lower than what you expect from the nameplate voltage and RPM:  Motors run a tad under saturation and the IR voltage drop in the windings works against you both when you are running as a motor and a generator so you have to deduct it twice when converting from motor to genny.  Raising the excitation to where the core saturates is about right to compensate.  It also tends to flat-top the waveform, which is actually better than sine if you're charging batteries.

Neos have a somewhat stronger field than an equal cross-section of saturated core silicon-steel, but the saturation of the steel under them limits their effective field unless it can spread out to a somewhat wider area.  (The excess that doesn't find magnetizable metal nearby folds back locally rather than penetrating the windings.)  So approximately paving the rotor pole areas with big rectangles works though is slightly overkill, while paving it with little disks (so the field only has a short way to spread to find enough steel, minimizing the extra "air gap" through the over-saturation metal) is about right (but might be pricier).

If flux says I'm wrong, listen to him not me.

[joestue]

Do not run it saturated, this is a 57HP motor.. not a 3 hp motor, you will burn it up!
As an induction motor, it should already be in the 87-90% efficiency range due to its size.
If you were to convert it to a synchronous motor properly engineered, theoretically the rotor has zero losses and you'll get a significant increase.
But if you run it saturated and you *double* the total iron loss, then you're probably looking at 3-6 hp needed just to turn it at 1500 rpm with no electrical load.

anyone care to speculate on whether or not you could pull the stack off, melt the aluminum out, then wind it with copper?
if you get lucky and the core lends itself to that easily, that's what i would try to, but who knows what the rotor looks like under the aluminum.

[SparWeb]

I've only cut apart single-digit HP rotors, so take this with a few grains of salt, but the rotor is made of steel disks, all identical, having a series of holes around the circumference and of course a big hole in the middle.  They are ultimately held together with the copper or aluminum that is cast through those holes.  The disks are skewed a bit so that the resulting copper "bars" have a skew of a few degrees.  There could be just one layer of these bars, but my 7.5 HP motor's rotor had 2 layers of such bars.  When I turned it down on the lathe, I didn't need to turn it down so much that the second layer of aluminum was greatly removed.  That left enough of the AL to keep the disks together, so I could use the rotor like that.  The last 3HP motor conversion did not have such an arrangement, so on the lathe I had removed all of the aluminum and the disks split apart well before I had the rotor turned down small enough to accept the magnet blocks.  Time for a new rotor in that case (all for the better).

You certainly can pull the disks off without damaging them, and melting out the aluminum doesn't sound hard if you have an oven that will do it.  I don't think these existing disks would be adaptable to rewinding...  Never thought about it before though.  I know who to ask, but they just might call me crazy before considering the question!

anyone care to speculate on whether or not you could pull the stack off, melt the aluminum out, then wind it with copper?
if you get lucky and the core lends itself to that easily, that's what i would try to, but who knows what the rotor looks like under the aluminum.