Wind Powered Batt Charger

[GeeBeeFan]

Lets see if I can explain my idea...
I've started going to college for my A&P License, which I'm really Geeked about :D Only problem is that I have to drive an hour each way to get to class everyday! This long drive leaves a lot of time to think about stuff. so on my drive home Friday(after my basic electricity class) it was really hot and I had all the windows open so as the air was rushing past I got to thinking about things and I thought it would be really cool to convert an electric motor to a generator, mount a prop on it and make some power! Then that lead me to think about what I could use the power for and it hit me, why cant I hook my battery charger to it? I mean this is basically taking the power system out of my plane, attaching it to my car, and reversing the electricity flow!
I'm just trying to figure out how to do it. I assume that I'd have to build my own charger to properly harness the generator's output? I was thinking along the lines of a 540 motor mounted to a simple stand that I can stick through the sunroof. and just a basic 11 inch APC prop that the LHS would have in stock. Another problem I thought of is how to regulate the power coming off of the generator, I mean I can set the cruise control and keep a fairly constant speed, but there's always those boneheads out there where I'll have to change speed for a while, so that will change the output. I'm trying to think of a way to keep a constant flow out of the generator. Maybe some kind of flow regulator built into the charger?
I dont even know if this would be practical or not. I know its much simpler to just plug into the wall, but it'd be nice to feel like I'm acctually accomplishing something while on my hour long drive! Plus I wouldn't have to waste time good flying time at home waiting to charge batts! I'm just trying to generate ideas right now, I dont want to start building something then find out it wont work! All comments welcome as always, Thanks.

[Comatose]

Well, this plan will work, but there's one thing you need to consider. The power going into the charger isn't free, its coming from your engine. So, from a practical standpoint, its easier and more efficient to just plug your charger into the cigarette lighter of your car.

Of course, no one drops by the DIY electronics forum to do things the easy or practical way, so here's my $.02.

What you're really going to need here is a switch mode power supply. A SEPIC or boostbuck supply, to be precise. With either topology, you can get a voltage either higher or lower than the input voltage. Barring that, a 12v buck converter would be a LOT easier, but it'll interrupt the charge if you have to slow below 12v.

To get around that, I'd use a 15v regulator and prop your generator to output ~24v at highway speeds. Get a little lead-acid battery (about 4 Ah, 12v). Now, have your buck converter feed the battery through a shottkey diode, so if the voltage of your generator drops below 15v, the battery doesn't discharge. Connect your charger to that 12V battery.

Or, just plug your charger into your your cigarette lighter. But what fun is that?

[GeeBeeFan]

Well, this plan will work, but there's one thing you need to consider. The power going into the charger isn't free, its coming from your engine. So, from a practical standpoint, its easier and more efficient to just plug your charger into the cigarette lighter of your car.

Of course, no one drops by the DIY electronics forum to do things the easy or practical way...
Plus a little propeller and motor sticking out of my sunroof will look cool going down the road!

I figure that it isn't really all that practical, but I dont think it would really be less efficient. I mean its not like I'll be producing much drag with this setup, and there isn't anything else thats putting a lag on the car's engine so its more like just using the wind energy that the engine happens to be making. Kind of like an overly complicated version of pluging into the cigarette lighter! I haven't much of a clue what most of the stuff you just listed off is but heck, that's half the fun! trying to figure out what's what and how it works.. Thanks for the info, I'll start looking at things. Thanks.

BTW: I thought it was a bad thing to run a batt charger with the car running...or is it the other way around?

[GeeBeeFan]

Okay, I think I'm starting to get it. Basically the Switch mode power supply will allow me to have an unconstant input but still have a constant output, correct? Then I hook that up to a lead-acid battery for "storage" and hook a normal charger to the lead-acid battery? So where can I get a power supply like this? is it something I could build? I guess I have some time to figure that out, I need to build the stand, get a decent generator and find the correct propeller for a 24v output.

[darkith]

http://www.otherpower.com/ has lots of information of power generation by various methods, including wind. It's much larger scale than what you're thinking, but most of the ideas are quite scalable.
In the "Experiments" category, they even have small "science-fair" generators using model airplane props...though they seem to have had better luck with large computer fans.

A link from there goes to http://www.fieldlines.com/story/2003/11/21/174123/16 which suggests that your actual power output is going to be quite low...

D.

[Foxy]

Larger stepper motors make great wind generators also. Due to the large number of poles they only need low RPM to start generating.

Adam

[GeeBeeFan]

Thanks for the tips everyone, I think I'm starting to get this stuff! I have a pair of 540 motors that I've had lying around for a while that I'll use to start with. I also work at the LHS so I have a LARGE selection of props that I can choose from. I think what they meant by the computer fans being better is that they start at a lower rpm. But since this will be mounted on my car going 70mph down the highway, I dont think low rpm will be an issue. I'll try a few things and see what I can come up with. I think I'll just worry about making power first, then worry about converting it. Thanks again.