Products > Electric Fence Chargers (general), p. 1
About Our Electric Fence Chargers
For a table showing which chargers are best for dealing with specific animals and situations, click here.
In general, each kind of low impedance electric fence charger that we offer is safe because the pulsed nature of the charge means a shocked person or animal has no difficulty letting go of the electric fence. Even so, there is always the remote possibility that an animal or person might get entangled in an electric fence, which is one reason why any electric fence charger above about 3 joules should be used with a modicum of caution.
By and large, the lower the electric fence wire, the more likely smaller creatures or children are to come in contact with the fence, and the more one should keep the joule rating down. As a rule of thumb, it makes sense to limit the joules to 1 joule per 10 pounds of body weight, so that the charger for a fence likely to be contacted by a 30-pound dog should not exceed 3 joules.
About Electric Fence Voltage
Volts are the electrical equivalent of pressure. So if you have a lot of volts on the line (4,000 or more) you have the ability to shock almost any creature. However, 4,000 volts are not always needed. One can reliably shock deer on the nose or tongue (using a baited fence) with 2,500 volts. Horses can be reliably shocked with 2,000 volts. And smaller animals (including dogs, cats, raccoons, rabbits, and ground hogs) can be reliably shocked with as little as 700 volts.
About Fence Power and Joules
Knowing about volts tells whether your fence has the electrical "pressure" needed to administer a shock (by causing an electric current to pass through the target animal) but tells little about the power of the shock. To know about the shock's power, you need to know something about the joules put out by your charger, the joule being a measure of pulse energy that for the electrically inclined is equal to amps x volts x seconds.
The joule ratings of different chargers can vary greatly. For instance, the ratings of those we offer here go all the way from the 0.14 joule rating of the SS-440 solar-powered charger to the 10+ joule ratings of the AC-powered DE-4000 and FM-180.
In general, the makers of solar-powered chargers are limited by the relatively small amount of electrical energy turned out by the charger's solar panel. Therefore, virtually all solar-powered chargers have a maximum legitimate joule rating not exceeding half a joule. This does not prevent the charger from putting out a high voltage, but it does mean that even strong solar-powered chargers have limited pulse energy and so have trouble powering very long fences and dealing with large weed burdens.
To a lesser degree this same problem afflicts battery-powered chargers, because large-capacity batteries are both heavy and expensive. Therefore, to keep the battery from having to be overly hefty or from being drawn down and having to be recharged all the time, the makers of battery-powered chargers generally limit their chargers' maximum pulse energy to 2 joules or less.
Refining things a bit further, one should note that a charger's joule rating is not the same as its joule output. The joule rating (assigned by the manufacturer or other rater) is the charger's maximum reputed joule output. However, the actual output can vary a good deal, depending upon fence conditions (most notably the weed/brush burden) and does not always correspond closely to the assigned rating. Among other things, there is no reason to put out more than about 3 joules unless there is a need for greater power. So the makers of the strongest chargers (see for example the DE-4000 and FGM-180) typically arrange things so that their chargers will put out only about 3 joules when the weed burden is low (creating something like a 500-ohm circuit) but will raise the joule output as weeds and brush cause the circuit resistance to decline (see individual charger descriptions for specific data).
Finally, it's worth noting that hefty joules may not be needed or desired in some situations. If you are going camping at one place 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.
Conversely, 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 fence. So in this case a low joule rating is desired.
On the other hand, you may want to use a charger with a high joule rating on a permanent fence designed to exclude predators. For example, say you want to protect beehives from bears. If you use a weak charger, a bear may be surprised at first by the slight shock, but as it becomes familiar with the fence it may decide that the honey is worth a mild zap. So you need a strong charger that will administer a considerable jolt to repel him. More generally, it is wise to use a strong charger to power fences in situations where one or more predators might become accustomed the fence and willing to ignore anything but a strong shock.