building microwind and microhydro generators

The automotive (and marine) alternators that I am familiar with have a field winding on the rotor, Any permanent magnetism in the rotor is just residual magnetism remaining from the last time the field was energized. The output current of the alternator is controlled by controlling the field current.

Not in my experience (although one of the alternators on my boat apparently has no external field current terminal - but I'm not going to open it up to see why it works!)

I think that for your application, you do not need to worry about the AC frequency produced by the alternator. You should use the DC output to charge batteries, then use an inverter powered by those batteries to produce AC when/if you need it. By using batteries, you can store power generated on windy days for use on calm days.

I think the maximum RPM for many alternators is around 5000 RPM, and the AC frequency will be 600 - 1200 Hz.

I suggest that you look at some alternator manufacturers' web sites, such as

Also, google for "off-grid power" to find web sites discussing independent power systems.

Thanks Peter!

I just found this, as a further answer to my question. It is taken from an advert for a high output alternator in Ebay:

This alternator will drop right in place of your existing (factory) 90-amp unit and operates with the existing ecm voltage regulator.

If a common truck alternator can actually generate 90 amp at ~12 volt at the stated RPMs above, then it if a homemade wind turbine can physically get it to turn at this RPM, as with a pulley ratio, this would compete extremely well with the very best homemade wind generators I have been able to find online in which the actual alternator components were handmade.

So even if these alternators are not efficient, and even if they are not of optimal design, as in lacking permanent magnets, they are quite efficient compared to the handmade alternators that do have permanent magnets.

Having would coils by hand, I know this is a delicate process and am not surprised if a factory made car alternator is better than what I could make by hand with what is theoretically superior design and materials.

If there are no serious objections, I think I should just go ahead and try the car alternator.

Dominic

You most likely are talking about a brushless alternator.

Still functionally the same as the old style brush alternators except for the method used to energize the rotor.

Instead of brushes, they use a DC coil that surrounds the rotor into a slotted groove of the rotor or a side plate, in this area, the rotor has a pick up coil that generates energy from the DC magnetic field as its moving through it. This will excite the field and not much current is needed for this.

This removes the need for brushes and also allows for a tighter moister seal on the encasement of the coil..

often the rotor has an electromagnet which is powered by slip-rings , and this power is switched to control the output of the altenator.

very few automotive altenators provide external AC terminals, most have the rectifiers built-in, the aotomotice mechanics still call them altenators though.

marine ones could be permanenent magnet, all the auto one's I've seen had an electromagnet rotor.

On the other hand marine ones could have a stationary field winding and a rotor that redistributes the field.

vee pulleys have lots of friction. but it's possible a grooved of toothed belt could work. chain or gears may be a better method,

typically 5 or 6 of each north and south on the rotor, so

and roughly how many RPM when the engine is at

idle RPM 500-1000 (larger engines are slower)