How does a 220v outlet charge a 9000v electric fence energizer?



..if it can even do that?

I’m setting up a temporary fence for a couple of horses and I’m so confused, I find energizers with 12volts and ones with 20.000 volts. I’ve borrowed one with 9500 volts, and 1,5 joule, that I’m hoping won’t fry my thread (0,35 ohm, one copper thread and 4 stainless steel ones).

In: Engineering

There are two main features of electricity that are often referenced: Voltage and amperage. An analogy for those terms is to imagine water flowing through a pipe, where voltage is the pressure of the water and amperage is the volume of the water.

With electricity you can transform between the two, sacrificing amperage to increase the voltage. The device that does this is called a “transformer” and there is one in the energizer for your fence wire. Very high voltage with low amperage can let the electricity give creatures a shock without dangerously frying them.

Well, volts and energy aren’t the same. A standard 220v outlet (to my knowledge – I live in the states so I don’t work with 220v standards) outputs up to 10 amps. That’s 2,200 watts (volts times amps). As long as energy/power are conserved, you can play with the voltage quite a bit. You can bump your voltage up tenfold, but your current must decrease by tenfold as well. 2,200 volts? 1 amp. At 9,000v you’d be at 0.24 amps, assuming 100% conversion efficiency.

If something tries to draw too much current (amps) the voltage drops – this is conservation of energy stepping in to maintain the balance.

For AC, voltages are very easily stepped up and down using a transformer.

What fries wires is the amount of current flowing. The resistance of the wire causes energy loss through heat using the formula I^2 * R where R is the resistance of the wire. If too much current flows through the wire this heat generates too high a temperature in the wire which causes it to melt (or burn)

For any domestic appliance, the voltages alone won’t cause failure as long as the current flow is managed. Of course if you tried to generate some ridiculous voltage – you can theoretically ionize air molecules that can spark across small airgaps (which is what we call lightning when mother nature does this)

Most fence chargers aren’t continuous; they don’t run a current through the line at all times, but instead pulse. That way, the line gives a repeating stinging sensation rather than a continuous burn or buzz.

They do this using capacitors – devices which accumulate and store a charge, then discharge everything at once. It’s like plugging a drain and turning on the faucet. The faucet (the power outlet) fills the sink (the capacitor) with water (charge). When you pull the plug and dump all the water, that’s the same as a capacitor discharging. A capacitor can complete its cycle a lot faster than you can fill and drain a sink, but the principle is the same.

Input voltage determines how fast the capacitor will charge. As Phage0070 already noted, you can trade amperage for voltage, and the power supply in the fence charger does just that. For the purposes of livestock, you want high voltage, and *very* low amperage. (Voltage stings, but amperage kills.) So, the power supply trades in amperage for voltage, yielding a very high voltage, very low amperage pulse every time the capacitor discharges.

1.5J is not a lot of power at all. It is about the energy required to heat up 4g of copper by one degree C. And that is the energy that is contained in one pulse. The electric fence energizer outputs a high voltage but very low current and therefore there is very little energy in it. On top of that it only outputs a single pulse about once a second which further reduces its energy throughput. It is specifically designed to hurt you but not do any damage. They can use different circuits to get the high voltage that they need. They charge up capacitors which takes about a second and then discharges them over the outputs. And despite the high voltages involved there is very little energy in them.

My best guess:

From technical perspective, a transformer is likely used. Transformers convert A/C at one voltage to A/C at another voltage. If your fence is D/C (typical) you can add a diode (or full wave bridge) and a capacitor on the output side to convert the A/C to D/C.

The controller has a hot lead (connected to fence) and a ground. The circuit is basically open so it draws little to nothing UNTIL something touches the fence. Conceptually the electricity leaves the controller, travels through the wire, through the thing that touched the wire, into the ground, and “back to the controller”.

Electric fences TYPICALLY have a 1/5000 sec or so pulse width. So they can source a decent jolt (max current AVAILABLE could, theory, be almost 3k amps from a capacitor). The ACTUAL current drawn depends on the distance from the controller (resistance in wire) and the animal connection to ground (dry animal is low current (high resistance in dry skin), wet animal is bigger current draw, mostly travelling through the water on the skin not the skin itself) and finally the ground conditions (dry ground, is high resistance low current, wet ground is better connection so lower resistance and more current).

The wire will survive because the pulse is short (lots of time to cool down relatively speaking makes it hard to melt it).

Any of that help?