Friday, September 6, 2013

Energizer Impedance

Southeast Iowa has been dry for the last few weeks. Last year we went over drought fencing tips. This year we thought we would go over energizer impedance.

Impedance is similar to resistance. For energizers it means the level of ohms (resistance) that matches an energizer’s peak output. If low ohms then it's a low-impedance energizer. 

The first fence energizers (50+ years ago) were high-impedance units. Their maximum output occurred when the fence was weed-free. They could cope with drier soils but were very vulnerable to weed contact. Most were too small in output to be effective against difficult animals. The next generation was low-impedance energizers. They coped well with high weed contact but not with dry soils or poor conductors. They work best against low-resistance animals (cattle, horses, pigs) standing on moist soils.

“Wide-impedance” is Premier’s term for newer units that perform well in both dry and wet soils and in green and brown grass. In dry soils or with animals of high resistance (goats, wildlife and poultry), wide-impedance units out perform low-impedance units of similar output. 

The graph below compares 2 low-impedance units with a wide-impedance energizer (the 506). 
  • Note when each excelled. 
  • Note also that the larger low-impedance unit did better than its low-impedance little brother in all conditions.

  1. An energizer’s output is not a constant. The stated number on the outside of the box is a peak. It’s never more than stated and almost always much less.
  2. The shape of the curve is important. The chart illustrates 2 output curves, in joules. One is that of a wide-impedance energizer with 2.7 joule peak output. The other a low-impedance charger with twice (5.2 joules) the peak output. 
  3. The low-impedance unit excels when the soil is moist, the grass is green, the animal is a good conductor and there are plenty of ground rods.
  4. Wide-impedance units excel at stopping animals when the total resistance is higher, the grass is brown, the soil is drier (but not arid), the animal is not a good conductor and the ground rod(s) are less in total length.
  5. The higher an energizer’s peak joule output is at 500Ω, the more likely it will be effective when there is high green-weed contact on the wires close to the ground. 
  6. The higher an energizer’s output in joules at 5000Ω, the more likely it is to be effective when the soil becomes dry.

Wide-impedance energizers are able to deliver high-pulse energy levels and high voltages through a wider range of fence situations—including those with high total fence circuit resistance due to inferior polywire/netting; dry, sandy, rocky soils; dry, brown grass; and fewer ground rods. Animals have greater respect for and fear of fences energized by wide-impedance units.

Joules of pulse energy at the end of the fence (and thus the potential pain available to animals) drop as the total resistance of the fence circuit increases—due to wet soils becoming dry, reliance upon stainless steel polywire and tape fences, or fencing across sandy/rocky soils. Low-impedance energizers deliver high pain potentials when the resistance is low (hence their well-deserved reputation for working well when the soil is moist and the grass is green), but much less as the combined resistance of the soil, animal and wire rises.