Mother's Electric Fence Charger

July/August 1982

http://www.motherearthnews.com/Do-It-Yourself/1982-07-01/Make-An-Electric-Fence-

Charger.aspx

By the Mother Earth News editors

Justin and Krystal made this Pdf from Web so in future if you want or need for livestock

then here is circuits and all for a fence charger.

Footloose livestock and the crop losses that resulted combined to "spark" our creative talents.

Whether you're growing vegetables or raising critters (and especially if you're doing both), you

know the importance of keeping hungry livestock in their place. Of course, barbed wire will

usually serve as an effective deterrent to all but the most determined animals. For those few

headstrong beasties, though, an electric fence might be just the ticket . . . and it requires less

sturdy, and thus often less expensive, posts than would a barbed wire enclosure.

However, if you were to buy a fence charger at your local farm supply house, that piece of

equipment would probably set you back between $25 and $35. You'll be glad to know, then, that

it's possible to make this component on your own-using readily available, and some easily

salvageable, electronic parts and the information given here-for as little as $10 or $15.

HARDWORKING . . . AND HOT!

The charger we put together is powered by a 12-volt automotive battery, and can deliver an

attention-getting 25,000 volts of electricity to the fence strands once every second. Built around a

standard car ignition coil, the device hasn't enough amperage to seriously harm or to kill an

animal, but its "bite" will certainly serve to reinforce the concept that territorial boundaries do

exist!

Essentially, the salvaged coil does much the same job as it did under the hood of a car, but a

simple relay replaces the breaker points. When that device's contacts are closed, current flows

through the coil, which has the ability to store energy. Then, when the contacts come open (thus

breaking the circuit), the pent-up power has no place to go, and the magnetic field collapses . . .

inducing current in the coil's secondary winding. Because there are many more turns in this latter

wrap than there are in the primary winding, the voltage is amplified considerably and then

passed directly to the conductive fence wire.

The relay is energized for only an instant - actually about 15/ 1,000 of a second since the current

flow is controlled by a single basic integrated circuit. Housing 32 individually connected

transistors, this 79d electronic marvel generates a pulse (with a little help from a couple of timing

circuits) every second or so, activating the relay. A variable resistor can be used to adjust the rate

of pulse.

BUILD IT FOR A SONG

click here to enlarge

For the sake of your parts-shopping convenience, our materials list includes standard Radio

Shack components and catalog numbers. The items can all be purchased from your local retail

outlet for about $11, with the exception of the ignition coil and the printed circuit board.

The coil-which must be from a conventional automotive ignition system rather than the newer

transistorized versions should be easy to scrounge, or perhaps purchase for a pittance at a

wrecking yard.

The circuit board can be obtained in several ways, as well. If you have some experience with

electronic do-it-yourself projects, you may wish to make up your own from the full-size pattern

shown below. (Even if you have absolutely no such experience, you could still try your hand at

boardmaking, using a printed circuit kit available from Radio Shack.)

Another option is to buy a ready-made, predrilled board manufactured specifically for this

project by Danocinths, Inc. (see the materials list for ordering information).

The rest of the job is easy: Simply insert the parts into their respective holes, following the layout

guide. (Remember, it is critical that you observe the direction and polarity of the components.)

Once the pieces are in place, use rosin-core solder and a small pencil iron to fasten them to the

board. Try to avoid producing an excessive buildup of the conductive melt or allowing it to

bridge two adjacent paths.

Next, cut five 12" lengths of 18- or 20gauge insulated wire and fasten them through the board's

quintet of in-line holes . . . which lead to the ground, power, earth, and two coil terminals (it

doesn't matter, at this point, which wire goes where). Then set the circuit board aside and begin

assembling a protective enclosure for the electrical components.

Though any nonconductive material will do for this job, we chose to make a simple shed . . .

using a 46" length of 1 X 5, a 7-1/2" X 14" piece of 3/4" plywood, an 18" scrap of 1 " corner

molding, and a hunk of plexiglass measuring 9" X 15". (A piece of Masonite hardboard could be

substituted for this last part, but only if it's sufficiently waterproofed first.)

Start by cutting the wooden parts to the sizes indicated in the diagram on the following page.

Note that the two wall pieces and the corner moldings-will have to be mitered to 45 . Then

assemble the box, using No. 7 X 11/4" flathead wood screws where indicated and making sure

that the heads are countersunk and the joints protected with putty or silicone sealant.

Now, drill two 1/4" holes (they'll accommodate the two battery terminals) through the right and

left walls, and bore four more 1/4" openings through the back wall: one each for the high tension

lead, the coil mount, and the earth terminal, plus a final hole, near the roof peak, to allow you to

hang the unit. You can also, at this time, coat all the wooden parts with a protective water-

repellent sealer such as polyurethane.

With that done, go on to trim the plexiglass face cover to size and prepare to install it to the front

of the box with No. 4 X 3/8" roundhead wood screws. To make the assembly job easier, you'll

probably want to cut the cover in half, horizontally, about 7" below its peak . . . and then mount

the circuit board to the lower section of plexiglass with four No. 2 X 1-1/4" roundhead machine

screws, nuts, and 1 " spacers. Then, while you're at it, install the toggle switch. (Before screwing

either cover in place, though, be sure to run the proper wires to 1/4"-bolt negative battery and

earth terminals, hook up the coil and mount it with another 1/4" fastener-making certain its high

tension lead isn't routed near the sensitive electronic components as it passes through the back of

the box-and wire the switch into the positive battery lead, at a point before the terminal, as

shown in the illustration.)

All that's left, then, is to mount the corner molding to the face of the roof peak (over the

plexiglass cover), using No. 7 X 1/2" flathead wood screws . . . waterproof these remaining

sections . . . and install the. battery cables and some claw terminal clips at the ends of the exterior

wires.

USE IT FOR MONTHS

This homemade fence charger is, of course, hooked up in the same way as are the store-bought

ones. We simply hung the box on a convenient fencepost, placed a 12-volt auto battery-raised off

the ground -beneath it, and drove a 4-foot bare steel rod into the earth near the site. (If you

choose to build another enclosure to protect the battery from the weather, as shown on the cover

of this issue, make sure you provide vent holes to allow any combustible gases to escape.)

The positive and negative leads go to their respective terminals on the battery, the terminal

labeled "earth" should be connected to the buried steel rod with a piece of (preferably insulated)

wire, and the high voltage lead gets clipped directly to the bare fence strand.

Keep in mind, though, that the "hot" fence wire will do its job only if it's [1] insulated from both

the fenceposts and the ground with standard ceramic or plastic knobs (of course, you could try

homemade protectors such as bottle necks or PVC pipe sections), and [2] placed at an

appropriate height for the animals you're trying to train.

Remember, too, that you can run several strands of fence wire at different levels if they're simply

tied together by a connecting conductive wire. This arrangement will allow you to keep both

adult and young beasts from passing through your chosen borders.

Given tight connections and a healthy battery, your fence charger ought to function for several

months without a "boost" . . . and the unit itself should last for quite a while before any

component part gives up.

Additionally, since the pulse rate is adjustable, you can stretch the device's working life a bit by

starting it off at a rapid rate, then, after a few days (by which time most of your critters will have

learned their lessons), cutting it back by turning down the variable resistor.

If you're interested in tinkering and don't mind saving a few bucks in the bargain, do consider

building this little hotbox ... we're willing to bet that your garden (or your neighbors!) will thank

you for it.