Wednesday, February 16, 2011

How an Alternator Works & how to make it work for you!

More and more people are now using alternators to make generators for renewable energy purposes.  I have my truck outfited with multiple alternators and 750aH battery bank so if my house ever loses power (no sun or wind for a few days), I can simply plug my truck into my house system and roll off of that.

Many people (including myself) are using older GM alternators to make small wind turbines, and they do work pretty well and parts are cheap!

OK- so you wanna' know how they work, and how to make em' work with your renewable energy setup.

We'll cover a few areas here.
1. General How It Works stuff
2. AC Power & DC Power
3. How to make it work as a wind turbine
4. Making a backup generator with an alternator

1. How It Works
An alternator is nothing more than a small generator. The alternator in your car is a 12v alternator and has an internal voltage regulator. Your average alternator consists of a few components..
A rotor, a stator, a voltage regulator, a bridge rectifier, and diodes. It's a very simple design. The rotor spins inside of the stator and creates an electrical field. This field is carried out of the stator via 3 phase AC into a bridge rectifier which converts the 3 phase AC (alternating current) into DC (direct current). The DC is regulated by the voltage regulator which is usually preset to 12v (14.2v charge rate).
This is hooked to your battery and viola - you have a 12v charging system and all your accessories like radio/wipers/climate control all work off the alternator while your car is running. An unregulated alternator can make 120v DC - but this would be bad inside of your vehicle - things would sizzle for sure. Most stock alternators used on a vehicle are anywhere from 80amps - 150amps depending on the application.  It is very possible to modify most alternators to produce anywhere up to 320 amps by changing a few of the components. This is commonly done to accommodate large stereo systems, police & emergency vehicles, and any other application that requires a lot of amps/current.

2. AC / DC - im not talking about the band!
Alternators make 3 phase AC. You can actually make your car alternator run more efficiently and last longer by running 3 phase to an external rectifier before your battery. When using the DC output post on the back of an alternator, you must use have gauge wire - depending on the application, it may be 1ga, or even 2/0 ga which is really expensive these days. The further you have to pull the DC, the heavier gauge wire you must use or it will create resistance and that creates heat -end result- your going to burn something up. Thats why the wires on your car battery are so thick.  Lets say you hook up a beefy car audio amplifier in the trunk and you have some crazy boom boom car stereo. You will need a heavy gauge wire to run to the back so you do not have any loss.
OR- you can tap the 3 tags of the stator, run a a smaller gauge extension cord and an external rectifier and this will be a lot cheaper, and your alternator will love you more for it. Then you would not need as much heavy gauge wire.
3. How to make an alternator into a wind turbine
Most commonly used today is the GM 10si and 12si series alternator.
If you just took your alternator out of your car and put it on your roof and slap some blades on it - it aint' gonna' work! There is a little modifying you must do first. First, you will need to gut the alternator. Take it completely apart. You must change the stator first because you want to hit system voltage at a much lower RPM. Stators are available online that will produce 12v in as little as 125rpm.
Next - the best practice would be to remove voltage regulator and bridge rectifier from the picture completely. Tap the 3 output tags from the stator- this is your 3phase output.  You can use a 10ga extension cord to carry the 3 phase AC- it will be a lot cheaper this way and its actually better for the alternator. So now you have an alternator with 3 wires hanging out of the back, and a heavy duty  extension cord going to where ever you need it to go. At the other end of the extension cord (where your batteries are) you will then hook up (a little beefier) bridge rectifier to convert your 3 phase into DC. A voltage regulator is NOT needed in a configuration like this. The batteries that you are charging will regulate the turbine.  Lets say you have a 12v system. When the turbine is spinning, it will start to tighten up (harder to spin) at 14.4 volts - thats when the magic happens and your batteries start to charge because you are now producing amps/current to force into the batteries.

4. Making a backup DC generator from an alternator
There is many ways to go about this. Some people use an old lawn mower or small gas motor mounted to some sort of chassis. As I mentioned in the beginning, I have made one out of my vehicle.
I added an additional alternator and batteries. If my house batteries ever die, I can plug my truck into my house and run from batteries as well as charge the dead battery bank simultaneously. This might not be that practical for the average homeowner,  so some people will make a scaled down version. You must use an alternator setup like a wind turbine for an application like this, but may want to go with a "high wind" model or build one with a higher rpm stator. Lets say you have an old lawn mower laying around and it still runs and you just cant bring yourself to toss it to the scrap heap. You make some sort of chassis to bolt the motor and alternator to, thro a belt on it and youre spinning! Obviously you cant just plug this into your panel and expect electricity- you would need a couple batteries and an inverter for that. Pulleys play a vital part in this as well. If you have a decent size pully on your motor and need to drive the alternator harder/faster, you want to use a smaller pulley on your alternator. In the automotive world, this would be known as an overdrive pulley. Making too much power and need to slow the alternator down? Do just the opposite and put on a larger pulley.
There are many ways to this and I could type for days, but this is a general idea to get the ball rolling.

As always - any questions, please feel free!


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  2. Have you thought about buying scrap? There are tons of alternator sells in Farmington, MN and plenty of other parts, so you might want to take a look so you can mass produce, make more money and/or figure something else out! It's a great opportunity while it's hitting the market!

  3. Hi,

    The most pragmatic article I have read so far, that even a layman like me could understand with ease.

    At present I am working on a set up for my home, which when successfully completed, will be passed on to my village folks to help them overcome power outages that occur very frequently besides huge power fluctuation.

    In my experiment I use, 1. 1.5HP - Single Phase Induction motor with 1420 RPM; 2. 12V Alternator with 30 amps.

    At the next level I am looking forward to using an engine that does not require any electricity and to only run my Induction motor so that I can save inverter output. If you can provide any guidance, it would be really helpful.


  4. I'm not sure what kind of stator to get. Do you have any specific suggestions or keywords to search by?

  5. Wow. Great article. Any way I can get more info on buying and replacing the stator for lower RPMs? Do you loose amperage or watts when you do this?

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  7. Do I have to have a battery if its going to be mounted to a windmill running nothing but a 12 volt spinny caution light that Im converting into a light house

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