Electric Fence Chargers, cont’d.
Still More Basics: What Does “Low Impedance” Mean? “Impedance,” like “joule,” is a technical term. In the world of electric fences it measures the resistance that the electrical state of a fence conductor presents to a particular electrical output moving forward along the line. 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.
However, not all low impedance chargers shock the same. When confronted with a larger weed or brush burden that drains electricity from the fence, some low impedance chargers increase their output only slightly or not at all, and so the voltage on the fence declines sharply. In contrast, other low impedance chargers increase their output sharply to compensate for the electrical drainage. As a result, a 0.75 joule charger that compensates this way may outperform a 2 or 3 joule charger that does not compensate–and as an added bonus only provides a maximum 0.75 joule shock when there is no weed or brush burden–in contrast to the “more powerful” charger that provides a 2 or 3 joule jolt that may be stronger than what one would ideally want. The product pages that provide details about our various chargers indicate how well each of them compensates this way.
How Powerful Should a Charger Be? This brings up the question of what one needs in the way of joules. The answer is that one needs enough joules to maintain at least 2 kilovolts on the line, and also enough joules to provide a jolt that the animals involved will respect. However, one can have too many joules. For instance, suppose you are putting electric fence wires up to protect a barrier fence around a paddock. In that case the barrier fence is doing the job of confining the animals, weeds and brush pose no problem, there is little room to run, and giving a major jolt to a horse unfamiliar with the arrangement could panic the horse and do more harm than good. So in this case you should use a low-key charger with a very low joule rating, something like the Dare Enforcer 80 with 0.2 stored joules (product 01-24A), the Zareba Yellow Jacket with 0.25 stored joules (product 01-23), or the Dare DS140/DSX140 with 0.35 stored joules (products 01-26 and 01-26A).
This rule about keeping the joules low in small enclosures also applies to most small portable electric fences–because the flimsy one or two runs of half-inch tape on plastic step-in posts are only providing guidance to horses that are pretty amenable to being confined anyway; giving a big jolt under these circumstances is less likely to support confinement than it is to spark a breakout; weeds and brush are not a problem, or shouldn’t be; and so long as grounding conditions are reasonably good (marginally moist unfrozen ground) there is every reason to think that a low-key charger will do the job. What’s more, if grounding conditions are not good the best answer is not to get a more powerful charger but to alternate actively charged runs of conductor with other conductor runs that are not charged but are instead wired up to the ground terminal on the charger.
As the enclosure becomes larger, and the posts and conductors more substantial, even a temporary electric horse fence begins to take on some of the qualities of a barrier horse fence. Here there is reason to use a stronger charger, typically one with a rating of a joule or more. Since the enclosure is larger, should a horse become frightened it will have some room to run. And the longer fence, lower runs of conductor, and potential weed and brush problems all militate in favor of a more powerful charger. All this is doubly true of a permanent electric horse fence that is used instead of a barrier fence and that may extend for many miles. It is true that the best answer to weed and brush problems is regular maintenance; and the best answer to a fence overly long for its conductors is installation of high-quality polyconductors (see products 02-35 and 02-61 thru 02-64, and 02-95) or polycoated wire (product 02-66). If one has a really low run of conductor on the fence, the weed problem can be reduced by using one or more weed burden protectors (product 16-04).
Even so, one can expect more problems with conductance, gates, connections, weeds, and brush on a longer electric fence with more conductors than one would have on a shorter electric fence with fewer conductors, and one should certainly have a charger that is powerful enough to deal with the task at hand. In most cases a 3-joule charger will do the job, and there are virtually no cases where a charger more powerful than the 13-joule Field Guardian General is needed. Underwriters tend to get edgy about endorsing fence chargers as the joule count climbs over 15, and one should be prudent in considering the use of any charger over 2 joules in areas where people are unfamiliar with electric fences and in places where there could be unexpected meetings between members of the public and the fence.
