Automotive Alternators as Windgen's

[daleh007]

Just found this site and have a few questions. A little background, I have a little place over in Central Oregon in the "high desert" where the wind is usually more in the moderate range (summer) to just plain howlin (winter). I have taken a look at some of the different homebrew designs and am aware of them. I was looking at the internet the other day and found a site advertising wind gen plans using an automotive alternator. I have read some of the posted info about automotive alternators but have a few more questions:

1. Are car alternators designed to run at full output, say 60 amps, for extended periods of time or will it burn out the diodes, bearings etc?
   
2. Do automotive alternators have built in regulators or are they external and further what is the charge profile. What does the regulator look at to determine charge rate?
   
3. Assuming you have to use a pulley system to bring up the RPM's on the alternator what are ball park figures regarding rotor size, necessary min. wind speed and cut-in speeds for charging.
   
   

Thanks

[DanB]

There's been a bit on this - if you search the board here you'll find some comments on the topic.  

Ill answer your questions the best I can... (I could be wrong as usual!)

" Are car alternators designed to run at full output, say 60 amps, for extended periods of time or will it burn out the diodes, bearings etc? "

They should be able to do that continuously.

"Do automotive alternators have built in regulators or are they external "

The come both ways.  They regulate the current which is sent to the field which controls the flux through the stator coils.

 "What does the regulator look at to determine charge rate?"

Battery voltage.

Here is an argument against persuing this much further.

They wont be very efficient, especially in low winds.  Since they do not contain permanent magnets, the field (which is how they are regulated) is a big electromagnet - which draws power.  The first 30 - 50 watts you generate is required to energize the field of the alternator.  That's power wasted... and in most medium/low winds... it may be most, if not all your power.

They like to go real fast, so you will need to gear (belt) it up significantly.  Figure you have something like an 8' prop (a reasonable size for a car alternator probably)...  in low/average 10mph winds, you may have 100 watts available at the shaft or so (if its a good prop).  Thats about a 1/8 HP motor!  Your belt will suck it all up - if not, energizing the field will.

Between energizing the field of the alternator, and the belt - it will probabably perform quite badly except in strong winds.

The regulator that goes with car alternator would not be appropriate... it would disconnect the machine from the load when the batteries were full, so that your wind turbine blade would be "free-spinning" - which is usually a dangerous and noisy situation.  Most wind turbines are regulated by dumping xtra power into a load... usually a heater.  The wind turbine should always be hooked to the batteries and always under a load.  

So while I think a car alternator could work, I believe there are probably much better solutions.  When you consider the cost of a tower, batteries - building a machine etc... it doesn't make sense to me, to build around a car alternator and wind up with a highly compromised design.

[daleh007]

A small point but how does the regulator look at the battery voltage of approx. 12.5v when it's typically supplying the system with something around 14v? Maybe the regulator stops the generation process occasionally to measure only the battery voltage?

[DanB]

I should've said .. it looks at system voltage.

It will always try to keep battery voltage at the same spot (usally around 14 volts) - and the regulator will control the field so that it produces however much current is necessary to do so.  If the battery is full charged, and there is no other load on the system (headlights etc...) then the regulator cuts back the field so that less current is produced.  But the voltage is supposed to remain fairly constant.

This is a bit of an issue also, with alternators that have regulators built in.  Sometimes folks will build gas powered battery chargers, using car alternators with built in regulators.  If the line, between the charger and the battery is long (and or thin) then the regulator will be fooled by the voltage drop and the alternator will produce very little current... thinking the battery is full, when it's not.  When I build gas chargers I prefer to get simple alternators that have no regulator, and simply use a resistor (sometimes a light bulb works nicely) to feed the field, then you can force them to do whatever you want (up to their current rating).

[hiker]

i rewired the stator on my car  alt--with finer wire and a lot more turns..

discconected the field[the electric mag]..cut down 1/4" off of each leg on

the rotor--glued on some harddrive mags--works great--higher volts at a lower rpm..

[tecker]

   I've got an alternator sitting here waiting for my drill press to fix itself. I guess the thing is not capable of that It just knows how to screw up mill bits. Anyhow

I'm down with auto altermnators , compact light and with magnets for lowspeed and the armature for high speed looks like hands down is the best choice . Needs some good bearings .Thier tough but it takes some torque to start .

The fingers on the armature take all the magnet alignment problems out .  

[Nando]

dale007:

Car alternators are low in efficiency, around 55 to 60 %, also the energy needed to feed the field is large specially at low wind velocities.

My suggestion is to get a brushless permanent magnet DC motor that can be operated as a generator.

I have some that are capable of producing about 1 watt per RPM, so at 600 RPM about 600 watts are generated.

Since you are just starting to think about wind mills, it is best for you to get books and read and as well, I suggest that you take course that teach the construction of wind mills.

I am including two attachments of a brushless DC PMG, that I have available for any interested.

Regards

Nando