Smallest solar electric fence energiser – For reforestation projects

Hi all,

I'm looking to develop the smallest/cheapest possible electric fence energiser that can run on a small solar cell, and charge an active wire of just 1 to 4m in length. The application is to protect individual trees in reforestation projects, where cows and other creatures can take a very destructive interest. To be able to deploy a single unit for each tree, would avoid the costs of wiring and/or fencing that can be prohibitive to install and maintain. If the cost could come down to $5/unit in production, it'd be a very feasible product.

Normally, an energiser delivers a pulse of maybe 3-4000V, approx once per second, to energise the active wire. It uses an earth spike to allow the circuit to be completed when the unwelcome intruder touches the active, gets a shock and hopefully runs away.

What I don't know at this stage is what size of pulse is required (in joules) to be effective. If a prototype allowed pulse size and frequency to be varied, then those parameters to tested and set for production.

There are many cheap solar garden lights on the market, which have small panel and batteries integrated; I'm thinking that this kind of basic product could be adapted to include the high-voltage circuitry, to do this job.

Any advice most welcome!

Thanks,
Paul

Interesting idea, but your price target could be very difficult to impossible to meet. Electric fence energizers have to meet very stringent safety requirements, these are laid out in a standard, which you normally have to buy( see BS EN 60335-2-76 for example). Additionally, to meet these requirements, a new unit would have to be tested to the standards, which is an expensive process, I worked in a business where the units were tested in New Zealand. You could avoid these processes, but if anyone was injured or killed by a unit, there will be problems.
I have included a few links below, they have some general information, but you really need to buy the standards, which cover such things as the energy delivered etc.
https://agrar.horizont.com/cms/en/service/regulations.html
https://mro.massey.ac.nz/bitstream/handle/101...d=C9DBB8290BF921924900CB3A54556BB8?sequence=1
https://professional-electrician.com/technical/electric-fence-controllers/
Cheers,
Richard

Thanks Richard. I didn't consider that a design that would be struggling to be effective at all might risk being actually dangerous; but you have a point!

So let's consider this just as a design exercise, and leave the certification issue for later. My question is firstly whether the device is feasible at all, at this kind of ballpark unit production cost.

Thanks.

China is the place to look for the solar components I would imagine. Battery capacity is another issue, the solar cell will no doubt be obscured by foliage for long periods of time, let alone the cloudy days you will encounter. This may mean a larger battery and solar array than you might initially guess at.
You need to do the maths on the power consumption, then look at how long you need the controller to run off the battery alone, as well as the recharge time available. Met records may be helpfull.
Looking at the design of the controller, there are basic circuits available, there was one in the second link. You would need to price the high voltage components out first, since these are likely to be the most expensive, in particular the transformer (wound components, unless off the shelf, can be expensive) and high voltage capacitor. It may be worth looking at some of the commercially available solar fence controllers to a feel for what is needed. This will be a challenging design exercise, I wish you well,
cheers,
Richard

And thanks again Richard.

I found one simple circuit shown in a couple of places:

https://www.quora.com/What-is-an-electric-fen...r-with-a-circuit-diagram-and-how-does-it-work
https://chathunka.wordpress.com/2013/01/19/electric-shock-circuit/

So maybe this is a starting point. But to be honest I don't understand how it works; or what specific components to use (the transistor and transformer in particular). I've also tried a couple of the circuit design/simulation sites, but not yet succeeded in creating a working circuit, since I'm not finding the components.

Any hints, on how this thing functions, or how I can play with it?

Thanks again

Paul.

There are so many home grown high voltage circuits for electric fence controllers that it can be mind numbing. I don't think that the circuit you are looking at is much help, there are plenty of circuits that can produce a high voltage, but that doesn't make them a fence energizer. Some of the ideas presented might work, you would need to test them with stock, allowing for near short conditions, since vegetation around the trees could well end up shorting the unit. Problem is that very few will produce a pulse with the right amount of energy in the pulse envelope. This is needed for safety reasons, to overcome partial shorts on the output (grass is the most common one, along with tree branches), bad grounds, and still produce something that will get through an animals hide.
Circuit simulation is straight forward at a basic level, you don't need to have a specific transistor or component, in most cases a generic one will do initially. In the case of active components, you will normally be able to find something with similar characteristics, you have to extract the most relevant data from the data sheet to do so.
What simulator are you using?
There is an interesting item here which you can download that covers the design of a typical commercial unit controller.https://www.researchgate.net/publication/224687331_An_Electric_Fence_Energizer_Design_Method/link/54b7a3420cf2e68eb2803590/download
Note that the DC voltage input normally comes from a mains supply, in the case of solar you need to use a dc/dc converter, and that may mean designing for a different DC supply to the output side of the electric fence controller to get a more efficient design.
Hope that is of some help,
cheers,
Richard

Thanks again Richard.

I've signed up with CircuitLab, and created this circuit there.

Just don't know what components to use or how to get the simulation going.

Paul