Homebrew 12 volt Generator
First off, and unfortunately, the ARRL has seen fit to hide this information from the sight of non-members. Personally, I find that to be an abomination and discriminatory. So, all I am allowed to do, is give you the link to the page.
The 12 Volt Pup: A DC Generator You Can Build
This is a pretty cool little generator, and depending on how good you are with your hands (and your brain); you should be able to come up with an alternative style or package, (if you will.) The author, of the original documentation, called his design "The Pup". Mine shall remain nameless.
I have no objections to anyone copying my design or version of this generator as long as it is made for home or personal use, and not produced for sale or profit.
The main ingredients for this little mix-master are pretty simple:
1- 5 to 10 horsepower lawn mower or other gas engine.
1- 60 to 100 amp alternator.
1- Ammeter
1- Volt meter
Bear in mind; the larger the engine you use, the better it will work and run. A 5 hp is barely adequate to turn the alternator under any kind of a load above 8 to 10 amps. If you are trying to charge a very low car battery, or run your entire shack on 12 volts, it will require a minimum of 15 to 25 amps or higher. "The higher the amps load; the harder the alternator is to turn - hence, more horsepower is required to turn it."
Also, I prefer to use a horizontal shaft engine, instead of a vertical. The reason being, most vehicle type alternators are not equipped with adequate thrust bearings for vertical mounting; they just were not designed that way. Besides, it is easier to find a higher horsepower horizontal shaft, than vertical. Roto-tiller engines usually start out at about 7hp and go up. If you can find an old roto-tiller, in tact, the drive pulleys will come in very handy, along with some of the control cabling and hardware.
The alternator can be of any make (Ford, Chevy or whatever) as long as it is rated for at least 60 amps and has the built in voltage regulator circuitry. You can find a used one at most any junkyard. If you prefer, you can buy a reconditioned one at your local auto parts store. To be honest, there probably would not be that much difference in price.
The volt and ammeter can be purchased at the same parts store, or you can buy a cheaper set at one of the "all-in-one" stores. The object here is for relative readings only. The voltmeter measurement should go to at least 18 volts, and the ammeter should go to 30 amps. A 60-amp meter would be better, but harder to find. Both meters should be back lit. Remember, the alternator needs a momentary low-level power source to energize it. (3 - 5 volts) should be sufficient.
There are a number of variations you can do. For example, if you look at the second picture, on the right-hand side, you can see two rather large capacitors. These were purchased at a Ham auction, for 5 cents each. At one time, they were used by a telephone company; probably as part of a backup power system. They are rated at 18 volts, peak surge. My idea was to create a battery eliminator system that would allow the generator to be used without a battery attached. They also act as spike protection, when the system is grounded with a ground rod. (This is something you should always do with any generator; AC or DC). These little jewels also have a charged shelf life, of almost a year. They will slowly discharge on their own, but I have yet to find them below 9 volts. When wired into the exciter circuit with a little momentary push button, you should never need an external exciter voltage. Just push the button until you see the voltmeter show a 14-volt charge. Your alternator should have a connection for the exciter circuit, built in. Read the paperwork that comes with your alternator! BE VERY CAREFUL WITH ALL OF YOUR WIRING. KNOW WHAT YOU ARE DOING, OR GET HELP FROM SOMEONE THAT DOES! I claim no responsibility for damage or injuries!
In the last picture on the right, you can see my 700-watt inverter (DC to AC). Again, it will only handle what your system is designed for. With a 7hp engine, I can use this to power a 10-amp DC power supply or run "small" AC powered tools, like drills, skill saws and laptop computers. (Not at the same time, of course). If you have a well-charged car battery attached, the performance will be greatly enhanced. You should be able to run your laptop, 10-amp power supply, and a 4-watt night light (above your shack table). When in the dark, a night-light will do wondrous things. Even a 12-volt car backup light bulb, with proper reflectivity will provide very adequate light.
Here is the basic circuitry. Beyond this, your are on your own. The link to the pictures is at the bottom of the page. (You may have to refresh this page a few times, before you can see the pictures)