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Three Phase Motor for a Wind Generator

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joethemechanic

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dalmatiangirl61, Dropping out of society and off the grid like a Dagny Taggart dropping into her own Galt's Gulch :)

So many questions my head hurts but I'll pick away at them

So much trouble reworking this motor. Not to say it wouldn't work, and I don't doubt you could do it. Not to mention a 900 RPM motor is a good choice to start with.

First off no matter what you do with the rotor magnetically you are only going to end up with two poles. When they are talking about poles on an AC electric motor, they are referring to how the stator is wound.

You might want to check out this book, years ago when I had a lot of the same questions, it answered them for me. Look for an older edition, probably the older the better for your purposes. Although the later ones are good too.

"Electrical Machine, Drives, and Power Systems", by Theodore Wildi

I think you will be better off finding a good source of electric forklift junk. The DC drive motors are quite siezeable and will macke a good generator of the size you need without modifications. Just make sure you get a "Shunt Field" version, and NOT a "Series Field" version.

The problem with the 120 volt battery bank is that as the cells age you will get unbalanced charging among the cells. I had the same idea once. It worked good at first. Then I started to end up with overcharged cells and undercharged cells. I have some friends in the SLA industrial battery manufacturing business and they told me their father had the same idea back in the 1940's and ended up with the same unbalanced cell charging problems.

But your forklift junk will be either 36 or 48 volt and that seems to be a very practical voltage for SLA storage batteries.

Not to mention you can find good deals on used electric forklift batteries. The cells are all separate so you can lots of times make a good one out of a couple bad ones by swapping cells.

Pumping water up 3,000 feet? Uggggggggg. The rule of thumb id you need 1 PSI for every 2 feet of lift. Down at the bottom of that well you are talking about having like 1,500 PSI. You are going to need like a 15 stage pump for that. I would lay a mile of pipe to the spring than have to overcome those problems.

But really check out that book, it is really a must read for the kind of project you are planning.

Oh yeah, you probably want to rethink you electric motor loads and utilize as many DC motors as possible. it will save lots of losses. Only use the inverter to power your electronics. Even your lighting can be DC.
 

Bloc911

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I have also been looking at those types of generators. They are calling them PMA's (Permanent Magnet Alternators) or PMG's (Perm. Mag. Generator). They are basically the same as used on most motorcycles but made with larger automotive style alternator casings. The rotor's electromag. core gets replaces with a perm. mag. and when turned by a motor, wind turbine... they generate electricity. After a lot of research, I like the one produced by Missouri Wind and Solar. They explain why and how they work and have several tutorial videos on how to make them yourself. The prices for the models they produce seem good compared to some of the other companies i have checked out. They can be powered by a variety of drives: wind, motor, water... and there a lots of sites and videos all using some variation of this same tech using every thing from old brake rotors, ceiling fan motors, tread mill motors, and a few that were trying different AC and DC motors like you are considering. They rewrap the coils with small diameter wire and figure out how to add magnets to the rotor and start spinning them to see how much power they get. Some do good, others not so hot. I have checked around 15 diff makers of PMA's and they come in a wide variety of designs and outputs as well as prices. Check around and you should be able to find some that suit you needs, or even be able to find good how to videos on how to take what you have and make one or more. Another note about PMA's to watch out for is whats called "coging". Like the teeth on gears when they rotate there is a perceptible vibration produced form the friction of the rotation. Some Pma's have a problem with this. Although they will produce power they have a harder time starting in wind applications, and are often subject to increased bearing wear. As far as I can tell, to negate the coging effect there needs to be an odd number of magnets if multiple individual magnets are used on the rotor. If a single large ring style magnet is used then it not as big of an issue. However the larger ring style magnets typically produce far less output than multiple individual magnets. The only other issue I have come across is heat. They will burn out if they get to hot just like any other motor or generator. Even in wind driven applications you need to make sure they will get adequate cooling. I like the auto style PMA's for this reason, the same fan that you find on them to cool them while in an engine bay can still be used on them when converted to a PMA for cooling. After that it all comes down to how you are going to connect it. Auto style PMA's can generate either AC or DC just not both at the same time. The electricity produce is wild and you will need to feed it in through a bridge rectifier and then in to you choice of inverter or conditioner components afterwards, as they will depend on your PMA's output type (AC or DC). I hope this helps.
 

Lyndon Strother

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04/21/2018
Your original design, machining in the 12 magnets will probably work fine. The concern one party had on inductive heating will not apply in this case. It won't matter about the laminations. Your original logic about the 12 pole design is sound. It will produce 60 HZ when run at it's original design speed (1200/1800/3600 RPM's...) and higher frequencies at higher speeds. It will likely produce the full voltage according to how you load it and how strong your magnets are. IF it is 3 phase, a set of 6 diodes, configured like in automotive alternators will convert it to full wave DC. The diodes or rectifiers could be anywhere down stream of the original windings. You can run it as variable Hz AC all the way to your shop or where ever you have your batteries/inverter ect. You would be best off to build it, test it to see what the output is, THEN decide on a suitable transformer to get it to the rough vacinity of the voltage you want to work with and put the rectifiers after the transformer. A standard 60 HZ Transformer will work down to about 25 HZ and up to 400HZ.
Most 3 phase motors are designed for dual voltage. IF your windmill is very far away from where you plan to locate the batteries and inverter you can configure it for the higher voltage (480) and you won't need as big of wire and you'll get less voltage drop. You can use a 3 phase transformer, or any of various combinations of 2 or 3 single phase transformers to get to the desired voltage.
Overcharging will likey be your biggest challenge. This set up would probably NOT work well with a standard battery charger. A lot of the standard battery chargers are not so efficient, and would be unhappy with the varing frequency and voltage input. You would want a combination of Zener Dioeds and some sort of electronic circuit to cut out the charge circuit once the batteries were fully charged.
A person who takes on a challenge of this nature deserves a good deal of respect, good luck with the project.
 

BTPost

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Lyndon, I like your thinking here.... If, on the receiving end of a 480 Vac Line you put a transformer, and FullWave Bride Rectifier, and then feed that into a MX60/80 MPPT Charge Controller, that has a 12-73 Vdc Input, and 3 Stage Charging Output, you would have the prefect Setup.... Just Say'en....
 

Motorwinder

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The three phase wind generators I’ve wound were 8 pole stator windings (900rpm) with regular squirrel cage rotors. They had a speed increaser on them, and ran around 1200 rpm. I don’t remember anything being special about the windings or the connections. These are the big wind turbines you see in California.

You turn a motor past it’s syncro speed and it will generate power. They will also generate power at syncro, or slower. Trust me, when we run big motors in the shop, you don’t want to tough the leads when the rotor is slowing down.

Frequency is determined by the rpm, and the stator poles. 60 HZ is 7200 divided by the number of poles.
 

Power

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A 208 volt 3 phase set will output nearly 300 volts after it's rectified to DC

Hmmm, that sounds like free power, which most of us agree is impossible. I thought when you rectified AC you were just chopping out half of the sine wave, please explain how/why voltage increases?


Dalmation,
We measure AC voltage RMS - root mean square. If you were to feed a resistance heater, RMS AC equals same dc voltage in heating value. RMS is .707 peak AC voltage, so 250 VAC RMS ac has a peak voltage of about 338 volts.
 

dalmatiangirl61

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Last Subscription Date
07/10/2019
Have not given up on this project, made a new shaft and rotor for a 1 hp motor (testing before doing larger motor), have box of neodymium magnets, just need to cut the slots and assemble. That project is on the bench in Texas, should be back on it by the first of the year.:wave:
 

Power

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I don't like higher voltage DC, and have concerns about 10 batteries in series. How do you keep one from discharging before others, getting reverse voltage and being ruined. How do you keep a weaker one from being overcharged?

That being said, I would go for a 24 or 32 volt truck generator. Come out with DC, use stock regulator to maintain batteries, less conversion losses - i.e. 3 ph to regulated DC & back. Then I would use an off shelf inverter to get 120 AC. Unlike most motors, the gen is already somewhat weatherized and designed for an environment with broad temperature swings, humidity and shaft speeds.


Save my time and energy for other problems will face building in the boonies and trying to marry solar & wind. Have Fun!
 

t6299fm

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09/12/2012
The generator powering this reply runs at 164 RPM
Hmmm, that sounds like free power, which most of us agree is impossible:D. I thought when you rectified AC you were just chopping out half of the sine wave, please explain how/why voltage increases?



Funny thing is I don't think so



Jim, thats what I've been proposing all along, the only question is how do I generate the power, so far as I know there are no off the shelf super low rpm generators. There are commercial wind generators available, 30K and up, and many look like a 3 phase motor.

Did some googling yesterday on "wild AC", most call it wild because input rpm is variable, they do not reference the winding pattern. The plans I had for wild AC dealt with the winding configuration, no matter what set rpm you turned it you did not get a usable AC power. The way it was explained, or at least the way I interpreted it was that battery charging only occured in the upper third of the sine wave in a rectified AC system. So on a single phase generator the time between sine wave peaks is long, a 3 phase system is better yet there are still valleys between the sine wave peaks. By winding it for wild AC you still only had 3 legs, but the windings for each leg were split into 2 or 3 locations on the stator, so when you ran the power through an O-scope it looked like 9 phase power and had no valleys in the sine wave. I have no clue as to why this winding pattern was developed or where it was used, best guess would be that someone in the early 1900's was trying to 3 phase wind generator:D

Heres a link to the brake rotor idea that supposedly is the answer to high powered low rpm 3 phase PM generatorshttp://www.backhomemagazine.com/NewImages/Premiums/Premium1Sample.pdf

This is probably the best built unit I've seen, but I see way too many flaws in its basic design, the most important being protection from the elements. I might just pay for a subscription to get the plans for this idea, then build on it. I was a subscriber to "Home Power" magazine for years, until it became less about designing/building off grid systems and more about where to buy ready made systems and how to install them.
 

cornbinder89

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I don't like higher voltage DC, and have concerns about 10 batteries in series. How do you keep one from discharging before others, getting reverse voltage and being ruined. How do you keep a weaker one from being overcharged?

That being said, I would go for a 24 or 32 volt truck generator. Come out with DC, use stock regulator to maintain batteries, less conversion losses - i.e. 3 ph to regulated DC & back. Then I would use an off shelf inverter to get 120 AC. Unlike most motors, the gen is already somewhat weatherized and designed for an environment with broad temperature swings, humidity and shaft speeds.


Save my time and energy for other problems will face building in the boonies and trying to marry solar & wind. Have Fun!
Everything Power said and more! With permanent magnets for the field, you can't control the output, so either your system has to be undersized for the load so it can always run at full output and you have a 2nd system that you can control or you need someway to control the blades to control the power input.
Elecro-magnet field has so many advantages, I just can't see why you would limit yourself to permanent. If you plan on using the motor stator as built and making a rotating field, I would suggest buying a used brushless truck alternator and studying how they do it, and scaling it up for your 30hp motor. Basically, a stationary coil has a shaft running thru it and a sinusoidal metal cage attached to the shaft that rotates between the coil and the stator. Hard to explain, easy to see when you pull one apart.
The field can be any voltage you want and the coil is a simple single coil on a bobbin wind.
Brushless design is almost mandatory, esp for something that will spend most of its time at "full field". Then the gen end becomes almost no maintance and the output can be controlled.
There are some good high output brushless truck alternators but the even at 100- 150 amps @ 24 volt would be low for what you want to do.
If you are planning to make a new rotor for that motor anyway, why not make it a electromagnetic field?
 

Vanman

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Last Subscription Date
07/10/2019
I would imagine that, if one wanted to use an off the shelf three phase motor as a stand-alone induction generator at variable speed, a VFD could be used for the purpose by connecting to it’s DC bus to extract the power, and running it in braking mode. Some are designed to work with a dynamic braking resistor, as well as to be linked to the DC buses of other VFDs to allow regenerative braking.

Keith
 

dalmatiangirl61

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Last Subscription Date
07/10/2019
This project was abandoned some years ago when I found PMAC servo motors, already built and tested for what I wanted to do, at scrap pricing. The 900 rpm motor went into the bucket in last years cleanout, too much stuff and I can't curate it all.

The largest servo motor in my stash will output 100 amps per leg iirc, at 1200 rpm, just need a property with running water to turn it, or a really big tower and prop:crazy:
 

cornbinder89

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This project was abandoned some years ago when I found PMAC servo motors, already built and tested for what I wanted to do, at scrap pricing. The 900 rpm motor went into the bucket in last years cleanout, too much stuff and I can't curate it all.

The largest servo motor in my stash will output 100 amps per leg iirc, at 1200 rpm, just need a property with running water to turn it, or a really big tower and prop:crazy:
Sorry, I didn't see how old the thread was.
 
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