3 Phase AC - DC

If you scan down this Wikipedia article, you'll see a rectifier for a 3 phase alternator (as used on a car). Such a rectifier consists of 6 diodes. You'd want to have diodes rated for perhaps 200 volts and 100 amps, although the actual values will depend upon the size of the alternator and battery bank. You'll need to mount them to a heat sink.

With a permanent magnet alternator, you cannot adjust field strength, so voltage will vary with speed. You may be able to use speed as the regulator. If you cannot, then regulating the voltage coming out of the alternator will be a little more costly than it would be with an adjustable field alternator. If you google some windmill sites, you can see what is available.

In my spare time, I am going to learn a little more about robotics :)

I was thinking about having the disk of coils which is the stator part of the design on a table bed that will move on a Z (up and down) axis. When the generator is spinning slow I could have the plate back off of the magnetic feild of the magnets to reduce magnetic drag. This might also be a way to have some controll over the amount of power generated at high powers...? Going to have to tinker with that idea.

But, first...diodes.

also...whats that in your picture? Some kind of super jet boat?

Great drawings. Looks like art.

A few things I've picked up here and there:

People say direct drive works best -- it rarely seems to make sense to use a gearbox. In terms of efficiency, this would have to be true, but there are times when you would like to trade efficiency for some voltage, I'd think: it's hard to charge 48 volt batteries with a generator putting out 30 volts. DC - DC converters can step up voltage, though. (There is a size at which you really have to have a gearbox -- really big mills turn too slowly for direct drive.)

I think you will never want to back the magnets away from the coils. Seems that if there is too much drag for the thing to spin under load, it would be better to reduce the load, than to decrease the efficiency.

At high power, regulation is often done into some sort of "dump load" like a water heater. If you've charged all your batteries and heated all your water, then you might want to sell electricity back to the grid, through an inverter.

The boat: it's a sailboat powered by a rigid wing... something I designed and built primarily to commercialize -- to sell in volume to windsurfers who were frustrated by not having enough wind. The idea was that it would give you high speeds in average winds (a little under three times windspeed). Secondarily, I was planning to go after the world sailing speed record with it. Couldn't get enough testing time on it before I had to get back to paying work, and without testing time, couldn't get funding. Catch 22. The boat works fine, and when I pick up the project again, I'll probably look first for sponsorship money, instead of development money.

Some other peculiar boats (and a bigger pic of mine):

http://www.solarnavigator.net/wing_sails.htm

Really interesting, wing sails have come a long way since I last took any interest.....

They are great applied physics exercises. Although they can have some advantages in convenience (e.g., I can leave my boat in the water with the wing up all the time -- it simply weathervanes on ball bearings) the real advantage is L/D, and that only becomes really significant at high ratios of boatspeed to windspeed. In the Little Americas Cup, wings are the only competitive way to go. On the other hand, a wing on a boat like a J-24 (a relatively sporty keel boat) would have no real advantage, and plenty of disadvantages.

Also fun, are boats with canted sails. I built a very simple proa (symmetrical about a plane 90 degrees to the usual one) with a canted sail, designed in such a way that the sail's force vector passed through the center of lateral resistance of the underwater foils. There was no heeling at all, no matter what the wind strength. It was almost eerie to sail.

I think the boat is awesome... the name Windski comes to mind!

My windmill project codename is "The Aerobine"!

The design to your sail is similar to the design to my wind blades. It really is amazing how much power there is in the wind.

its windy in my head.

its windy in my head.

I have that problem too, increasingly.

The boat's name is Windrocket, BTW.

Perhaps I can offer you a little more specific help. I will assume that you are not terribly interested in doing a lot of diode research yourself; or you would not have posted this question here. I will also have to guess that you have one of two common types of generators. 240V delta (industrial power) or 12V (automotive)

if you have the first case this is a good solution. http://www.microsemi.com/datasheets/2X101_100D30J_B.PDF

if you have the second case this is a good solution. http://www.onsemi.com/pub/Collateral/MBR4015CTL-D.PDF

The first is about $50 each (you will need 6). The second is about $2 each (again you will need 6). These are both available from Digikey so they are easy to buy. The second issue to remember is that diodes can be used in parallel to increase the current capacity or in series to increase the voltage capacity. The third thing to keep in mind when you are building your bridge is that the heat sink surface is not electrically isolated, in other words the heat sink is usually the same as one of the terminals (annode or cathode); so be carefull not to short it to the wrong thing.

Your second question is best answered by Ken in his previous post with the bridge configuration. He also brought up a good point to be very carefull with your voltages. RPM will determine the output somewhat but if you have an industrial generator (240V) you must not connect that to a 12V battery array and so on. if you had a little more information on your generator, this could be refined a little better.

You'll need either 3 or 6 diodes, depending on whether you want to do half or full-wave rectification. As for what type of diodes, you need rectifier diodes, but the specific type will depend on the generator voltage and current ratings.

Excellent point, however it should be noted that you loose a lot of efficency with half wave and your nominal DC output current and voltage go down. Be mindfull of the RMS current and voltage of half wave rectification. You will also have to install a larger output filter to get acceptable ripple in your DC output waveform.

This is my generator...a disk of coils (stator) and a disk of magnets. The disk of magnets is spinning above the coils. I posted this in a form before but have since made some modifications to the drawings. There are 3 coils per phase. There are 9 coils total. There are 6 arms of disk magnets...(3N and 3S).

Thanks for all of your help so far...its great information. Its not that I don't want to research it...electronics are not somthing that I have done a lot of direct work with. I am very interested in learning as much as I can and posted here to get some input from those that already figured this out. I suppose its very basic information, once you know.

Its hard to know all the answers when there are so many questions yet to be asked JT ;)

you have made a "home made" generator?

yes. Made my own coils...made my own disks out of plastic. The magnets are rare earth disks... .750 inches by .125 thick. There are 3 magnets per star spike for a total of 18 magnets. Been trying to figure this whole electricity generation thing out for some time now and seem to be getting close.

This design will be attached to my wind turbine that is 3/4 complete. I designed the wind blades last year. The project got put on hold for 8 months for several good reasons and it has only been the last few weeks that I have started to design the generator part. Forward motion...

Anyway...I am at the lab working on the disks today and am getting close to being ready to test.

I'm not sure this will work but it should...it better :)

that is outstanding; Most industrious. It sounds like what you have is similar to a "pancake motor" where the windings and magnets are like platters stacked, as opposed to the traditional design where the windings are stacked on end around the outside like a picket fence around the house.

I would venture to say from what I read here. You have this in the bag. I only wonder about 2 things now. 1) voltage control; so that you get a good output 2) mid band and peak voltage and current output. With that information you will be able to most easily desing your rectifier bridge.

Sounds like you have a good idea, but your statement, "Made my own coils...made my own disks out of plastic," has me a little concerned . . .

Have you produced any significant power with your alternator yet? Generators producing electrical power create heat also -- e.g. they're not 100% efficient. Plastic isn't the best material to put into a hot environment, so cooling should be one of your concerns along with your choice of diodes.

Generators and motors don't know (unlike thermos bottles) how much power you can get out of them or put into them, respetively, so it's up to you to control that. The only reason you can't get 5,000 watts of power out of a generator designed for 1,000 watts is heat. Things like wire and insulation start melting and messing up the whole program.

I'd like to hear more about your project as it progresses -- keep us informed!

well I am going to wire the coils together today...I had started thinking about the whole heat thing and plastic melting. The reason I am using plastic is because I was suggested to avoid metals such as steel and aluminum because they could have a charge induced into them and may add drag to the spinning disk.

But if the coils are going to melt the plastic you are right...it could get messy. I will give this some serious thought when I get back to the lab today. Perhaps there is a better solution yet.

The first generator will be operational by the weekend...I will take some photos and post some more specifics to power generation.

'Tis true that coils mounted on metal can and probably will develop eddy currents when passing through magnetic fields, which causes heating ('cause they're virtually short circuits).

I scavenged some pancake motors from old, large disk drives several years ago, and they were designed with ironless rotors, similar to your design, but without a disk to which the coils on your machine are mounted. Instead, they were built by forming coils parallel to the disk plane and pressed flat and coated with (probably) an epoxy resin to maintain its shape. Epoxy is good to over 300 deg F, and the disk drive motors weren't being used at maximum power anyway, so heat wasn't that much of a problem.

Nobody has mentioned the fact that standard automotive alternators use the frame of the alternator for a heat sink. The diodes are press fit into the aluminum.

Jester,

In a previous life I did some work on coils (for a very different purpose) but the deal was that we had very high current and were trying to avoid eddy currents and magnetization. We used plates of this stuff called G-10. It is a resin fabric that is fairly inflexible (mechanically speaking) but it was used for circuit boards in some applications. When we were cutting it out it reminded me of Kevlar fabric but many many layers glued together. The really slick part was that it could withstand tremendous amounts of heat.

So let me ask this...where will most of the heat go...into the diodes?

Well, some of the heat will be produced in the diodes: 0.7 V_drop X I (current) = P (power). Some will be produced by the coils or windings I²R (of wire) = P (power).

How much current do you expect to produce? How large (gauge) is the wire in the coils? The spacing between the magnets and the windings is a very relavent part of how much current you will get, so it should be as small as possible.

The diodes you choose should be rated at least at the current you hope to produce, and it won't hurt anything to choose diodes rated for 2 or 3 times that value. Keep in mind that the power dissipated by the diodes must be done by getting rid of the heat energy via heatsinks whether finned or not in order to keep the junction temperature of the diodes at 150^oC or so. A good treatise on heatsinks can be found at http://www.aavidthermalloy.com/technical/papers/pdfs/select.pdf and a fairly in-depth tutorial on diodes can be found at http://www.allaboutcircuits.com/vol_3/chpt_3/1.html

I applaud you for building your own generator, but I would be remiss if I didn't say that there's a lot to building your own generator to operate as efficiently as one may find on the market. I think you'll learn a lot between now and version 2 .

Jester, in this page there are circuits, I hope that they help you.

http://www.electronica2000.com/fuentes/cargadores.htm

hummm I'm sorry to say that my Spanish is less then not so good :)

My electric diagram reading skills are not much better. I will do some reading on the diagram symbols...i should then be able to read the diagrams...Thanks!

Jester, I see that these interested, you are not electrical or electronic, at night I send a diagram to you, with the codes of the components, at this moment am leaving.

Greetings

Jester,

I also speak no spanish what so ever but I will tell you from what I see they have built a half wave rectifier on the back of the transformer (to simulate DC) then added a smoothing capacitor (to more mimmic DC) then created a common circuit called an emmitter follower for current control. This is a fairly elligant and simple design for charging batteries. It will not do much in the way of offering much protection from spikes or other anomolies. Very good first order solution. Just remember that your design is going to be varible voltage dependant upon shaft RPM.

hi

i m tanveer from pakistan i can solve your paoblem if you tell me

1- what is the ampars ratting u need in DC voltage

2- what is your required voltage

3- do you want to variate your voltage e.g. 100v, 125v, in DC etc.

tanveer ahmad electronics engineer

indus_electronics@yahoo.com

I returned. I suppose that generating are between 13 to 17 volts, if you put more than a battery, put it in parallel. If it serves to you and you need more aid with the diagram, sends me a mail in CR4.

Jester,

Are you planning on building your own voltage regulator or just buying one?

thats a good question...that I have not thought much about.

If its easy enough to make my own I would like to give it a try...i mean... how hard could it be ?

If you do not know how hard it will be, buy one! There are plenty of good kits that you solder together yourself that could save you some money.....at least in Germany....!

I bet the USA has something similar, spoiled for choice might be your biggest problem!

It is easy. Most auto alternators put out 3 phi AC. Simply attach a 1/2 amp - 1 amp diode (IN4001 should work), to each phase. Make sure the arrow points away from the generator. Then tie the 3 ends together and connect to a big 1000 uFD, or better, capacitor to ground. Be sure the cap rated voltage is 50% greater than the operating voltage.

Dear Guest, he is looking for a voltage regulator.......

Why design your own? Voltage regulators can be bought at radio shack (cheaply). If you want something heavy duty, check the Newark catalog.

....that is exactly what I told him before you commented......!!!!

We are going round in circles......please read and comprehend before commenting, its much better that way!