Joules: Stored vs. Output

Joules: Stored vs. Output

What is the difference between stored joules and output joules in an energizer? The terms may seem interchangeable, but there’s a big difference. Knowing that difference can help you understand how your electric fence will perform.

joules on electric fencing

Stored Joules and Output Joules

Energizers generally have a capacitor that serves as a storage tank for electrical energy. The energy builds up in the capacitor until it reaches a set level. At that stage, it is permitted to discharge into the transformer, which takes that energy and raises the voltage while reducing the amperage (often called amps). With reduced amperage, a safe electrical shock is transmitted through your fence. The higher the amperage, the more dangerous the shock. 

The problem here is that transformers are not 100-percent efficient in this process. Most of the transformers in electric fence chargers are only about 60- to 75-percent efficient. This means that the joules of stored energy in the capacitor will not match the joules broadcast by the transformer. For example, if you measure 10 joules of stored energy in your capacitor, you will only get 6 joules out of your transformer that has a 60 percent efficiency.

The calculation is simple – just multiply your stored joules by your transformer efficiency rating. In the example above, the calculation is 10 joules x .60 efficiency.

Energizers: Look for Output Joule Listings

Neglecting to mention the loss of efficiency, a measurement called Output Joules, is how some energizer manufacturers fool their customers.

These companies offer energizers with high stored joule ratings and compare them to other energizers that list output joule ratings. The deceptive presentation can fool customers who do not understand the difference between stored joules and output joules. In truth, it’s only the output joules that matter.

Sure, marketing an energizer’s stored joules is accurate and legal, but it doesn’t mean that the electric fence will ever see that amount of joules when your charger is installed.

Zareba®: Chargers You Can Trust

You can be comfortable in knowing that our energizers are labeled clearly. We present our energizers in a way that means something to you.  If we say there is a 6 joule output, that means the wire (and animal) will see (and feel) the 6 joules of energy. 

More Help Understanding Your Fence

Are looking for more information about how your fence works? Or perhaps you need some guidance while you’re in the field. is ready to help.

For immediate help with one of our products, reach out to our dedicated and knowledgeable Consumer Care Team at 855-5-ZAREBA.

If you want to learn more about how electric fencing works or how it is installed, visit the Zareba® Learning Center, where you can find topics like these: