DC motors for wind power

There are some home made wind power generators that work a lot better. Most motors are built for torque and are supposed to turn a lot faster than a wind turbine, means what little power you have gets eaten up in a transmission. Current state of the art has permanent magnets securely mounted to a disk directly driven by the turbine and the stator windings mounted stationary to the housing.

But isn't that going to provide AC ? I got the impression from the post header, that the OP was specifically looking for direct generation of DC. If I was going to play with this 'on the cheap', I think I would experiment with a few different automotive alternators from scrappers. Built in reccy. Built in regulator. As long as you can get it turning fast enough, should be a reasonably good source of raw DC ?? And if you need AC line power, use it to charge batteries, and then run an inverter ...

Arfa

Sure... Everyone has them in stock. All you need to do is supply some numbers, starting with the average wind speed. That will determine how much power you can deliver, which will determine the size of the turbine, which will determine the RPM, which will determine the number of poles, which will determine the gearing, and which will eventually determine the specifications of your generator or alternator. When you're done with that, you might want to check on suitable wide input range DC to AC inverters. Oh yeah, you might need a tower:

Light reading and good references:

You might wanna subscribe to the magazine or get the back issues DVD:

Ideas:

and not so good ideas:

Yep. Actually a sandwitch of two stator windings with the permanent magnet in between, also known as a PM "pancake" generator/motor.

"PM Wind Generator Comparison of Different Topologies"

(this is a motor but it can also be used as a generator). Good photos of the construction.

Plenty more found with Google.

If you look on ebay you'll see many used treadmill PMDC motors sold for this use.

Choose your treadmill motor wisely:

to

If

y.

be

it

IIRC, alternators run faster than car engine speed so that means a lossy transmission from a slow propeller with a lot of drive torque. BTW, you'd get AC and then rectify to DC... not quiet clear from your post where your "AC" and "DC" should be. Good luck! Cheers, Roger

Find some old DC generators from autos before they started using an alternator. Don't know what you would use for a prop maybe some custom thing out of a polymer like a spinner for a child's toy.

A DC generator generates an AC waveform that is mechanically rectified by the commutator and brushes. Isn't it better to eliminate the comm and brushes (maintenance and friction losses) and rectify with diodes? That's what an alternator does, although its field is rotating while the DC motor/generator field is stationary.

Automobile wind generator... Something like this?

Sounds like an idea generated by an exuberant moron.

IIRC, alternators run faster than car engine speed so that means a lossy transmission from a slow propeller with a lot of drive torque. BTW, you'd get AC and then rectify to DC... not quiet clear from your post where your "AC" and "DC" should be. Good luck! Cheers, Roger

The drive pulley on my alternator is about the same size as the one on the engine, so alternator speed should be roughly equivalent to engine speed. I don't know whether modern car alternators still use rotating coils and slip rings, or rotating magnets and static coils, but either way, I wouldn't have expected there to have been a lot more mechanical losses than in the modern wind turbine alternators. You don't need to have a car alternator turning too fast before it reaches regulated voltage output, but I guess if you wanted to get much actual power from it, you might need to get it going quite fast, in which case, what you say about gearbox losses will of course, be true.

I'm not quite sure where you are having trouble understanding what I was saying about AC and DC. The op's original header said "DC motors for wind power". If you use a DC motor backwards, or indeed an old car generator - or dynamo if you like - to produce your wind driven output, then that output will be DC. No rectification required. That satisfies what he was asking. If, on the other hand, you use a rotating magnet, fixed stator coil generator, then this will be an alternator, and will produce AC, which will require rectifying to get to his originally stated requirement, yes ?

Arfa

Doesn't an alternator need a voltage on the field to make voltage and then you regulate the field to regulate the output?

I guess the choice would be up to the OP and his design to store/use the end product.

Well yes without the auto and with direct drive. I think the old Delco generators needed about 900 RPM before the reg snapped on and let charge voltage to the battery. My brother in law owns a 53 Chevy with the Blue Flame 6 Vette motor and a DC generator. I've worked on his voltage reg and it's very inefficient.

windings

DC.

should

slip

have

modern

course,

or

will

My mistake. I was thinking he was looking for some useful output rather than experimenting with toy motors for a science fair project. Most toy motors will make some power if you can spin it.

Useful output demands that you design and build your own or buy the equipment store bought for the purpose. Using automotive components requires optimizing the turbine some how to provide adequate torque at high RPM. The idea is to reduce the losses to the minimum AND design optimize the turbine AND the generator to the available wind. Also bear in mind that higher voltages reduce ohmic losses in electrical transmission.

One of the more useful designs for automotive generators and alternators, was the modified 55 gallon drum turbine on wheel bearings with belt drive.

I thought you might be amused. When I was in college, I had a 1960 Ford Falcon. It had a generator and mechanical regulator. That worked tolerably well until I discovered ham radio. The tube type mobile radios of the day used either dynamotor or vibrator power supplies, which were a severe drain on the vehicles electrical system:

I vaguely recall something like 6A per radio in receive and 20-60A on xmit. At my worst, I had 4ea Motorola 80D and 140D radios in the trunk. The rear springs were bottomed and I could not turn all 4 on at the same time. To save power, I also installed a "transistor powered" tube FM radio:

which burned an additional 2A. The generator was just not going to work. I eventually replaced it with an alternator, which worked much better.

In college, my Ford Falcon generator was converted into a wind generator. I have some print photos, but I can't find them. In order to make it work in light winds, I had to use a fairly large pulley ratio to get the minimum rpm. I don't recall the numbers, but it worked in a stiff breeze, and was useless at lower wind speeds.

The reason is that wind turbine output varies with the cube of the wind speed. That means that at low speeds, tiny changes in wind speed produce rather large changes in delivered power. The generator also has a rather non-linear shaft RPM to voltage output curve. If the two curves have their knee points superimposed by proper pulley ratio selection, which is the best one can do with such a combination, the result is miserable performance at low wind speeds, and a rather abrupt increase in output when the wind goes over the knee. As I recall, there were only two magnets (two poles) and a commutator in the automobile generator, while the typical PM wind generator might have 36 or more. The increased number of poles means that the PM generator will start producing output at 50 RPM, while the automobile generator will require about 1000 RPM.

There are also problems at the high end, but I won't go there.

I probably have some old alternative energy books on my shelf that offer plans for using an old automobile generator, but I couldn't find anything of the sort with Google. This should offer a clue as to its popularity. This sorta covers the alternatives:

and does not include the automobile generator.

An alternator (or, for that matter, a DC generator) need some magnetic field to sweep windings through. There's usually enough residual magnetic field in the iron from earlier running to get things started. The alternator on my standby-power set does this. If the residual is too small or gone, you gotta "flash" the machine with a brief current pulse from a storage battery to restore the residual.

Superman would use kryptonite instead.

Personally, I'm all for pouring the contents of the 55 gallon oil drum into the furnace of a power station, and then just plugging all my equipment into a socket on the wall of my house, connected to the power company's distribution grid ... :-)

Arfa

On 7/26/2009 8:26 AM Bryce spake thus:

No, an *alternator* does that (which is why it's so called). A generator just generates plain old DC. Like the ones on old VWs. No diodes.

Dunno how efficient they are compared with alternators, though.