Construct a low-cost battery-charging genset.

K. D. "Hoot" Gibson says he is "not an authority on much of anything, just a simple man living in the country and enjoying life very much ... This genset is a product of my imagination of over 40 years ago when I built my first one. I've since updated it when better components came along, e.g., the auto alternator!"

This is an abridged version of his plans. The original, copyrighted, photocopied version is available for $12 from CBE, Box 82, Clay City IL 62824.

What you'll need:

1. A good 5 hp gas engine (used on lawn mowers, tillers, etc.) with a horizontal shaft. You could probably use a 3 hp if you can't get a $ hp. You could also go larger if that's what you have access to. Ten or 12 hp engines work fine but use more fuel.

I prefer the horizontal shaft, but a vertical shaft will work just as well: it's just a little more difficult to build.

If you don't have an engine on hand, check used mower shops, junk yards, yard sales, flea markets, etc.

A used 3-5 hp Briggs & Stratton motor should cost $20 or so.

2. Get an alternator from a car or truck. It need not be large -- just in decent shape if bought used. I prefer an older model automobile generator with a built-in voltage regulator. I have a 75 amp GM unit from a 1992 Sunbird. It's small, low drag (easy to turn), and has an internal voltage regulator. It's also easy to mount and wire up and won't work the engine much. Chrysler also makes a good one but it doesn't have the built-in regulator.

(Ed. note: On an "update" page at the end, the author adds this: "After some thought and trials, we have determined it would be better to use a newer alternator (as I did with the 1992 Pontiac model) because of the increased efficiency over the older, larger units. These little ones are much easier to turn and will usually put out more power than the old units. ")

3. A 12 volt automobile or preferably-large truck battery or batteries. The number depends on how much power you want to store. The more batteries you have the less often you will have to start the engine, but it will take longer to Charge the batteries.

(Ed. note:He makes no mention of deep cycle batteries, which would be much more practical for this application. Larger industrial-type (or golf cart) batteries would be best, although these can be hard to find and expensive. However, marine batteries, commonly used for trolling motors, are common and relatively cheap, and will store more electricity and last longer than starter batteries.)

4. A power inverter. This is optional: you won't need it if you're using 12vdc lights and appliances. If you have to run anything on 120vac --refrigerator, water pump, furnace --you might as well bite the bullet and buy one.

They come in all sizes and prices. Wal-Mart has a nice-size one for $60 or so. I prefer a smaller one (about 600 watts) to keep price down as much as possible.

(Ed. note: Check your well pump or other intended application[s] to see bow much power you'll need. Wattage is usually found on the appliance label.)

5. Additional parts include the following, depending on which way you decide to construct this little jewel: belt, battery cables, lumber for battery racks, unit base, small 12 volt light, nails, bolts, nuts and washers.

For truly portable use, how about an old push mower frame with fairly decent wheels and handlebars?

If you can't stand the looks of this beast, get some paint.

You can also install a larger gas tank. I found a 20-gallon tank from an old John Deere combine. I didn't mount it directly to my genset, but in a rack of its own. Some 2x4s and 11x4s hold it quite nicely. Extra fuel hose can be bought along with a fuel valve. Leave your old tank on the motor, if it has one. Your unit will not be as portable but you won't have to fuel it as often.

You might also want a throttle cable to speed up the engine just a little above idle. It should run about 800 rpm or so. No need to have it screaming--the alternator will charge at slow speed as well as fast.

The unit has to set outside your living quarters! Carbon monoxide kills!

Set it outside in an outbuilding, if you have one. If not, think of someplace you can put it, out of the weather. Maybe a simple lean-to would work. Don't enclose it too tightly: it has to "breathe."

A long flex hose works well to help muffle the noise in addition to delivering the fumes, smoke and noise further from the house. This is a metal hose, flexible and 3/4" or 1" in diameter.

5. Wire selection: You will need some electrical wire. If you're using 120vac locate the inverter in your house. You will need to run a large conductor to carry the load. Get some 12-2 romax.

An extension cord (12 gauge) will work okay for 12vdc operation if you're just running lights and short distances, 50 feet or less. Over 50 feet, use 10 gauge wire.

Layout plans

Lay two 2x4s or 2x6s (about 36 inches long) on edge, side-by-side and about 16"-18" apart. This is your base.

Cut two more 2x4s or 6s the width of the base. Attach to each end of the base with screws or 12 penny nails. Motors vibrate and shake things loose: don't skimp on screws or nails.

Cut two 2"x8" pieces and place them inside the base where the motor will bolt down. Lay these flat and spike or screw them in, making sure they are flush with the top of the base. You will have to measure the hole pattern for your particular engine to know where to place these pieces.

Set the motor by drilling holes through the 2"x8" s the engine mounts on. Use same size bit as holes in base of motor. Bolt securely to base.

Lay the alternator on the top of the base and have a "look see." A good location will leave about 10" between the engine base and the alternator. You might want it different, which is fine. My thinking is that the shorter the belt, the less expense.

Cut two 2x2s, from oak, or angle iron if you have it, 8"-10" long. Line these skids alongside the alternator. Leave about 6" sticking past the alternator opposite the motor. Drill the same size hole as the alternator mounting through both skids. Install the large bolt through the skids and alternator and tighten hand-tight, then double-nut to keep it from loosening. Don't make this extremely tight because the alternator will have to be movable for belt tightening. (If you have the mounting bracket from the vehicle it sometimes simplifies the mounting of the alternator to the base.)

Set this unit on the base and install the belt. Pull the alternator until the belt is tight and mark the base top. Secure the skid to the top of the base with bolts, washers and nuts. Make sure these bolts are tight, and double-nut them.

The next step is rather tricky, but you can do it.

On top of the alternator is a threaded hole to secure the belt-tightening adjustment arm. Secure the alternator in a vertical position, keeping the belt tight.

The easiest way to adjust the belt is to use a "tarp" strap or large spring. An eye bolt 7/16" diameter x 4"-5" long makes a good anchor. Thread another bolt through the threaded hole in the top of the alternator and use that for the point of attachment there.

The belt needs to be tight or it will slip under a heavy load. Slipping belts soon wear out!

Now is a good time to stand back and look your "child" over. Let's start the rascal and see if it runs!

Run at a fast idle for a few moments. Is there any vibration in the base? If so, put some more braces between the base 2x4s/2x6s. You can also weight it down some or mount the entire unit on a mower frame, small trailer, etc. We don't want it "walking" while operating.

Making the electrical connections 

Hookup is simple. Check the wiring diagrams. Label both ends of each wire so they won't get mixed up and switched around.

You can run long distances from the battery if larger wire is used. The further you run, the greater the voltage drop. Over 50 feet, use 10 gauge.

Batteries can be set inside the house, basement, etc. Don't set batteries on dirt or concrete. That will sap a battery and ruin it. Set them on wood.

(Ed. note: Technically, batteries should be in a covered battery box, vented to the outdoors, because of the explosive gases generated by recharging. Also, batteries should be kept above freezing: lower temperatures greatly diminish their power and efficiency.)

Before firing it up again, double check all wiring. Reason: On some alternators, if you cross wires it will blow out the voltage regulator and/or diode. With this type of alternator you will have to turn on the switch for it to charge the batteries. Be sure to turn off the switch when the engine is shut off.

Everything correct? Fire up the dude and charge your batteries!

The secret to saving money by building this yourself is in locating used components. But even if you bought everything new, it would still be cheaper than buying a unit that has to run all the time.

Besides, you built it yourself: you know how it works, and you don't have to totally rely on others.

Be extremely careful while working around equipment, whether the tools used to build this unit or the unit itself when it's working.

Keep children away from this unit and batteries. Battery acid will blind you. Wear eye protection and leather gloves when working with batteries. The unit has an exposed belt which can also be dangerous.

S1: Single pole switch with switch box and cover (type used in houses to turn lights on and off). Mount on a vertical board mounted to the base. After the engine is running a moment or two, turn S1 "on" to activate the alternator. The batteries will not charge if the switch is "off." Turn the switch "off" when you shut off the engine, or the batteries will run down. Wire can be 12 gauge, black or red.

P1: Power wire that runs from the "Batt" post on back of the alternator to the positive (+) post on the battery. Should be 8 gauge stranded.

N1: Neutral wire from the alternator base to the negative post (-) on the battery. Use 8 gauge wire, white or bare.

C1: When making connections to batteries, remove insulation for about two inches. Wrap jumper wire tightly around 8 ga. wire and solder ... or lay the jumper wire alongside the 8 ga. wire and fasten it with a split bolt connector. Tighten the connector until it's tight!

Never cross or "tip" wires. Keep all positive wires to positive and all negative to negative.

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