Electric fence energizer problem

Thread Starter


Joined Nov 10, 2013
Hi, I'm new to the forum, so sorry if this problem has already been answered, but anyway...
My energiser is a mains type and is about 5 years old. Recently, the pulse has become very erratic, i.e. a normal even pulse of about 1 sec for a few pulses when first switched on, and then after a short period, no pulse for 10 secs or so, then intermittently with no set pattern. When it is pulsing, it is delivering a full charge to the fence. My question is, is it likely that the unit itself is defective and will need replacing as I suspect, or is there some other likely cause. I have no skills in working with electrical items as might be obvious!!!!!

Thread Starter


Joined Nov 10, 2013
I asked the question because I am not stupid and would never think of 'messing with lethal voltages'!!!!!!!!! A simple question merits a simple answer i.e. 'Yes it's knackered and needs replacing' Not a reply that you would give to a child!


Joined Apr 2, 2009
It's the forum policy. The thread needs to be moderated.

We will help after that.
We do not know ur age buddy.


Joined Apr 2, 2009
I have no skills in working with electrical items as might be obvious!!!!!
Electrical items is operated at mains voltage.
And you specifically said Fence Energizer, which to me means a shocking fence.

We do not want to endanger our members lives.

till moderation, how about posting some pictures of the energizer PCB


Joined Sep 17, 2013
I agree with R!F@@. By your own admission you "have no skills in working with electrical items". Other people reading your question may indeed be stupid so the warning is fully justified in the interests of their safety (if not yours).


Joined Nov 25, 2009
I don't want to be excessive when enforcing the ToS.

Devices designed to shock other people are banned, but not those designed to shock animals. However, I don't have any experience with electric fences and I'd like some input on this.
I believe we have allowed electric fences in past threads.

The power supply unit is the main culprit here, and if it proves to be directly powered from the mains, without an isolation transformer, then this thread will be closed.

So, whistleway, please understand that with your very limited background, tampering with your device can be dangerous and other members have every right to deny help that can be misinterpreted.


Joined Nov 7, 2013
I'm new here and don't understand the TOS. I've seen some of the silly ones like LED on mains.

I hope Isolated approved devices are OK to discuss and repair.

Most current fencers use a simple capacitive discharge system.

Both lines are brought in thru appropriately sized resistors.
Then bridge rectifier.
When a capacitor is charged to scr threshold it is dumped into primary of HV transformer, producing a short duration HV pulse output to the fence.

There are many protective devices. Caps/ neons, movs, gaps in circuit board etc. that are important for safety.

Some use more stable timing circuit.

Unfortunately for whistleway, me, and I think this forum, most circuitry is @ lines potential.

Most of the design and repair work I do is industrial and lines related, so I may not have picked the right forum to join.
I do enjoy it so far. And it seems many thoughtful answers are to be found here.

I don't know if it's allowed. But I could show a link to an inexpensive universal fencer board that replaces everything before the output transformer.

Yes it's line voltage, but plugs in with 4-1/4" qc terminals.

Seems answering questions with appropriate warnings and good information would do as much to promote safety as locking thread.
Last edited:


Joined Nov 7, 2013
Being recently retired I've got nothing better to do. :)
See if I can post a picture.

Not lethal, unless your bench is the barnyard, but contact with the capacitor would ruin your day.
And in case thread gets locked I'll add for good information.

All testing should use isolation transformer on workbench.


Thread Starter


Joined Nov 10, 2013
Has nobody read the post before replying. I asked a simple question 'My question is, is it likely that the unit itself is defective and will need replacing as I suspect, or is there some other likely cause'
I made no mention of me trying to repair it or in any way tamper with it, in fact, I don't think I could have been clearer. So if someone could answer the question, it would be of some help.


Joined Mar 24, 2008
I have designed electric fences from the ground up, but never messed with a commercial unit.

Does this unit have a battery, or is it powered from an outlet? It will still be converted to low voltage DC, then converted to high voltage pulses. If their is a battery involved measure the voltages on it. It also would not hurt to give use the make / model of the fence, many times schematics can be found on the web.

If it has a lead acid battery (such as a SLA, Sealed Lead Acid, which are quite common) I would suspect that first. Like car batteries, these have a limited shelf life.


Joined Apr 5, 2008

It sound like a heating problem to me, as you say it works at start-up, but goes erratic after some time.
It can either be a capacitor, transformer or transistor/thyristor/triac (depending on the schematic) in the circuit that goes out of specs.



Joined Sep 30, 2009
Before replacing the unit, how often do you 'walk' the fence? If there is vegetation growing around the fence wire it will cause the fencer to act funny. This is due to a slight grounding of the fence, until it drys out the green stuff.