Back to Information (Introduction)
For starters, read the answers to the paragraphs below entitled "Why are volts important?" "Why are joules important?" and "What is low impedance?" before proceeding to the Electric Fence Chargers section of the catalog. More briefly, if you have a short fence and few deer, get a 1-joule charger. If you have a more challenging situation get a 2 or 3 joule charger. If you have a choice (an AC outlet within 250 feet of your fence), you can save money by getting an AC-powered charger..
Volts are the electrical equivalent of pressure. They measure the urge electrons have to get off the charged wire and go elsewhere, just as pressure measures the urge of water molecules to burst out of a hose or faucet. The higher the voltage, the greater the charged wire's ability to shock some target creature that happens to touch the wire. In the case of deer, a voltage potential around 4 kilovolts (4,000 volts) will reliably shock a deer through its fur and skin, while around half this voltage (2,500 volts) will reliably shock it through its more conductive nose or tongue.
Such very high voltages are not dangerous unless they involve a large flow of electrons associated with a more or less continuous current. Today's "low impedance" chargers (see below) tend to be relatively safe because they produce very short bursts of electric output, typically lasting a few thousandths of a second, with the rest of the second being empty; and so, during the interval between pulses, a shocked creature or person has no difficulty letting go the wire.
Your fence's voltage determines whether it has the electrical "pressure" needed to administer a shock by pushing an electric current through the target animal; but it tells little about the power of that shock. That depends on the joules put out by the charger--which is why your charger's joule rating, gives a rough indication of the jolt likely to be received by a target animal. As a rule of thumb, chargers rated at half a joule or less should be considered weak, while those putting out three joules or more should be viewed as strong.
That says something about effectiveness, because some of the electric energy that a charger puts on the fence line is dissipated by resistance on the line and also by electricity leaving the line through weeds and brush—all of which diminishes the remaining joules and also diminishes the voltage available to shock target animals. At some point the voltage dips below the 4 kilovolts needed to reliably shock a deer through its fur and skin; and at some further point it drops below the 2.5 kilovolts needed to reliably administer a shock on the nose or tongue. So it's important to have good firm electrical connections on your fence, to keep plants and brush away from the charged wires, and if you are using polywire to know what length you can use before its internal resistance begins to significantly cut the joules and voltage on the line.
Nearly all the chargers used today are low impedance chargers. So what does "low impedance" mean?
"Impedance," like "joule," is a technical term. In the world of electric fences it measures the resistance that a fence wire presents to a particular electrical output moving down that wire. If the resistance is high the impedance is high, and if the resistance is low the impedance is low.
One way to lower resistance on the line is to let electricity received from an AC outlet or battery build up for a second or so and then to release it all in a very brief interval, say one thousandth of a second, with a very high electrical potential (a high voltage). So long as there is relatively little potential remaining from the preceding brief pulse, the new pulse will move out relatively unimpeded—hence the name "low impedance" charger.
If weeds are leaning on your fence, they offer the electricity a way of getting to the ground other than through the target animal. Hence, such a "weed burden," as it is known, can reduce both the voltage available to shock the target animal and the jolt received by that animal.
This fact has not escaped the attention of those who make fence chargers. They realize that few electric fences need to put out a jolt of more than about 3 joules. So the makers of the strongest chargers (6 to 10+ joules) typically arrange things so that their chargers put out about 3 joules when the weed burden is low, but raise their joule output as weeds and brush encroach and begin to drain power off the line.
It's worth noting that hefty joules may not be needed or desired in all cases. If you are going camping for a night or two, you can get some protection against bears or other predators with a fence of one or a few wires that has no weed burden and is powered by a charger with a very low (circa 0.35) joule rating. That's because the shock, though slight, is novel to the predator, and so the animal is likely to be surprised and move off. In the same vein, one needs neither hefty joules nor high voltages to shock small animals (raccoons, rabbits, woodchucks, etc.), and so weak chargers are useful for protecting gardens against such creatures. And of course, one does not want to strongly shock a horse in a small/temporary paddock, because that could panic the horse and cause it to charge through the other side of the paddock. So in these cases a low joule rating is acceptable and sometimes actively desired.
On the other hand, you may want to use a charger with a relatively high joule output on a permanent fence designed to exclude deer. That's because higher joule ratings tend to be associated with higher voltages, because you need 2,500 to 4,000 volts to reliably shock deer, and because a charger with a high joule rating is less likely to have its output voltage reduced by weeds and poor connections. Also, the stronger the charger's output the stronger the training effect, because of the relatively large jolt received by the target animal.
Solar panels are expensive, and virtually every solar charger sold as a single all-in-one unit is weak, putting out 0.5 joules or less. These chargers rarely put out the 4,000-plus volts needed to reliably shock a deer with an unbaited fence and commonly perform poorly even on baited fences. Hence, so far as deer fences are concerned, such chargers should not be entirely trusted.
Fortunately, a solar power revolution is underway that has been driving the price of solar panels down--and with it the price of solar-powered charger systems in the 1-2 joule range. As a result, we now offer 1 and 2 joule solar-powered systems suited to charging both baited and un-baited fences.