26 May 1995

MAINTAIN THE POWER TO SHOCK

Do livestock treat your electric fences with disdain? Shockingly good solutions to poor performance come from Gallaghers general manager, Barney Toulson. Tips are transmitted by Andrew Pearce

WITH spring winding itself up for the leap into summer, electric fence energisers are being disentangled from their winter bed of netting rolls and wire. After the lay-off some will work normally, some wont work at all and the iffy ones put away last season will still need fixing.

Portable units make up some 80% of the UK market, and their working environment is harsher than their mains-powered counterparts. Given farmers usual reluctance to fiddle with electronics (especially the sort which can bite back), dubious units usually either go in the bin or to a dealer for attention.

Often, though, simple checks can save a bill, improve marginal fence performance or resurrect a dead energiser. Procedures here centre on Gallagher units, but the principles apply to all makes.

A small first investment is a wise move, urges Barney Toulson. A purpose-built digital voltmeter (DVM) costs around £35 and is the only sensible tool for fence fault-finding, he says. Cheaper LED voltmeters give an indication of whats happening but are no use for earthing checks, while conventional meters cant handle the brief pulses which whip along a fence.

Where an energiser suits the type and length of fence it feeds but stock are not controlled, the problem lies with the unit, its earthing or the fence itself. Both here and in practice, problem-solving follows a logical sequence.

ENERGISER CHECKS

Start investigations at the energiser. Unhook it completely from the fence and earth spike, then read voltage at its output terminals (1). A healthy unit delivers at least 7,000V (7kV), with some reaching the legal maximum of 10,000V (10kV). On Gallagher units, slide the works from their casing and compare your value with the makers original test figure, which is recorded on a transformer sticker (2).

If the two are within shot of each other, the energiser is OK and the problem is in connections or the fence itself. Go on to section 2.

Battery

If energiser output voltage is low or non-existent, suspect the battery first. Dry cells need at least 8V to power energiser circuitry, while wet cells must show at least 12V (3). As a battery tires, the more intelligent energisers show its condition by LED and hold output voltage constant, but increase the interval between pulses. Others just stop working.

Tip: Battery choice. Specify deep-cycle/deep-discharge 12V wet batteries. These cost much the same as car or tractor versions, but are built to withstand complete flattening – so last longer – and will supply level voltage right up to discharge.

Look hard at battery clips, leads and connections. Rust on crocodile clips or oxidation on battery terminals makes a high-resistance barrier to electrical flow, and stops power reaching the energiser. Clean everything!

Internal investigations

Energiser output still low or missing? Then delve inside. Knowing what goes on inside the ticking box is useful in diagnosis; see Panel.

Slide off the units outer cover and inspect the modules fuse (4). Old age, reversed battery leads or too much input voltage can blow it.

If the fuse is OK, check connections around the module, capacitor and transformer. Gallagher energisers are built on the replaceable block principle, with push-home connectors linking the main bits. Damp corrodes connector surfaces, producing a high-resistance joint and lowering or blocking output (5). Clean connector halves then coat with Vaseline.

Deeper still

Three main blocks make up the unit – the circuit-carrying module, the capacitor and the transformer. Peer closely at the module, because its responsible for around 80% of all failures. Check the top side for broken leads and the brown stain of blown components. Underneath, look for broken copper tracks, which with caution may be repairable (6).

More often than not electronic failure is invisible. Even if individual component(s) are clearly blown, its very seldom worth replacing them as damage to circuitry on either side is highly likely.

Dealers usually hold spare boards, and the simplest way to confirm module failure is to substitute a good one. A replacement for Gallaghers mid-sized portable B150 unit costs £42, less 30% on production of the old one for exchange. Protect the replacement against water damage by spraying with a non-conductive, non-sticky silicon fluid before putting everything back together.

Capacitor failure is less likely. Before checking, discharge any stored energy by connecting a 100ohm resistor (bought from any electronics shop) between its output leads. Dont just short leads together, as this can hurt the internals. Rough-check a capacitor by setting an analogue (needle-type) multimeter to resistance mode and connecting it between terminals. If the needle swings full scale and slowly falls back, the capacitor is good. If it stays at full scale, the capacitor has had it; a new one for a medium-sized energiser costs around £14 .

Transformer failure is also possible. Ideally check by slotting in a replacement, pinched from a duplicate energiser if you have one. If not, lift off the module and look for signs of damage. Then use a multimeter to measure resistance, first between the two terminals carrying small-diameter wire and then the pair with larger wires attached. Complete resistance in either case, ie. an open circuit, confirms a broken winding.

LEADS, FENCE AND EARTHING PROBLEMS

At least 3kV is needed to hammer the "not today" message into livestocks consciousness. But even when the energiser is producing the goods, the jolt at the fence will often be below par. The problem must then lie with connections, the fence, or earthing.

Once the energiser has been pronounced fit, compare its output to voltage on the fence itself (7). A big difference suggests fence problems, but first eliminate poor connections. Rusty clips on the energisers output or earth leads will choke energy transfer, as will rust on the fence wire. Winding the units copper output lead around fence strands is a bad move, as current flow quickly promotes corrosion where they touch.

If connections are sound, walk the fence. Measure voltage every 100m or so, looking for a gradual or sudden drop. Breaks in flexible steel wire are obvious and produce an immediate drop to zero volts, but breaks in multi-strand polywire are not. To pinpoint a break in this, track back towards the energiser after finding a drop, measuring more often as you go.

Vegetation touching fence wire leaks power down to earth. Fence voltage drops sharply when the leakage point(s) are close to the energiser, but slowly when leakage is far down the fence line – Diag. 1 should make this clear. Listen for the snap of sparks jumping a poor connection or tracking to earth as you walk.

Fencings biggest problem

With all faults fixed, voltage all along the fence should be close to energiser output. But stock may still be able to touch the fence and get away with it.

The digital tester only measures voltage, or the potential for electrical activity between the fence wire and earth. For an animal to feel a shock, current must flow round a completed circuit. The current path is simple – from the energiser, along the fence, through the animal (ouch!) and back to the energisers earth connection.

Heres something worth writing in letters of fire, Barney Toulson suggests: A POOR EARTH CAUSES THE BIGGEST PROBLEM IN ELECTRIC FENCING. Electrons surge through the soil on a broad front on their way back to the energiser, and only an effective earthing system can capture enough of them to generate a sharp shock.

Luckily a digital volt meter finds earth faults, though the user can unintentionally do the same by touching the earth spike while the energiser is on. If you jump, theres an earth fault.

More formal testing is less painful. Simulate animal contact by bridging the fence to earth with several lengths of clean steel, putting these at least 100m from the energiser. This produces a high flow of electrons trying to get back to the unit. Then measure voltage between the energisers earth spike and the soil (8). Where more than one spike is in use, check at the one farthest from the energiser.

Ideally, no more than 200V (0.2kV) should register on the meter, but up to 400V (0.4kV) is acceptable. If the reading is greater, daisy-chain one or more extra earth spikes together until voltage between the last and the soil falls below 0.4kV.

Spikes are best made from galvanised pipe to resist current-blocking rust, each should be at least 1m (3ft) long (for medium-sized units) and individuals should be at spaced 3m (10ft) apart. More, and longer, earth spikes will be needed for larger energisers as higher current flows have to accommodated.

Where possible, drive spikes into moist ground. In sandy land, an earthing kit (£49) provides extra spikes and a highly conductive bentonite mix to set them in.

With semi-permanent fences, check earthing through the season. Clay soils can shrink away from spikes during summer, progressively lowering fence performance. And in very dry conditions, even in the UK, resistance between the animal and ground may be so high that little or no current flows and the beast feels no shock. In such circumstances, pray for rain – although by the time things get that bad, you were probably on your knees already. &#42

Portable energisers make up some 80% of the UK electric fencer market. But problems with the equipment can be hard to pin down unless you know what to look for.

7 Connected to the fence, this energiser puts out a measly 2.0kV – not enough to deter stock properly. But isolated from it, output jumped to over 7kV. Thus the problem must be somewhere in the fence, connections or earthing.

Diag 1: A DVM tester is very handy when walking a fence, as voltage drops to zero immediately after a break. But vegetation touching the wire somewhere along its length gives falling readings – see Diag 2.

Left: 4 First port of call for internal checks is the modules fuse. Use only the right amperage replacement – a spare is usually provided – or risk major module damage. Clean dirty fuse holder connections too.

Above left: 5 Portable energisers are left in some rum old places, and damp eventually corrodes plug-in connectors. Shine these up and coat with Vaseline, then spray everything with non-conductive silicon de-watering fluid. Choose something non-sticky, as blundering insects are a major cause of blown circuits.

Above right: 6 Module copper tracks can corrode and fail. It may be worth bridging the damaged area with a length of soldered-in wire, but other damage may already have happened or be caused by the heat of soldering. Gallagher always recommends a service exchange unit.

8 Check earth quality by measuring voltage between the energiser spike and the soil – see text for procedure. 0.9kV is much too high; bring it down to 0.2kV or less by adding extra spike(s) and connecting these together.

Diag 2: Vegetation leaks current to earth. When the problem is distant from the energiser, voltage drops as the trouble spot nears. Where greenery bridges the fence close by the power source, voltage falls faster.

Left: 1 First step in tracking down poor performance is to disconnect the energiser completely from the fence and measure its output with a purpose-made voltage tester; Gallaghers DVM costs around £35. Here output is a crackling 8.1kV, confirming that the unit and battery are good. To find what output should be…

Above left: 2 …Open the case and find the transformers information sticker. On this one the factory recorded 7.37kV after 24 hours running, so its 8.1kV test performance is excellent. With any unit, suspect a problem if output is much below 7kV.

Above right: 3 Battery voltage must be good. Look for at least 12V with wet-cell types, 8V minimum with dry cells.