Basic electrical question involving an electric fencer.

[jandrewg]

I had a recent dispute with someone and I wanted to see what the truth of the matter might be.

I have a friend who works on a farm. They have an electric fencer that is charged via solar cells. Fencers work in the following way. You attach the possitive leed of the fencer to the fence wire which is not grounded and then bury grounding rods in the ground. The fencer pulses the current through the fence(the wire is not constantly hot so as not to drain too much electricity). When cattle touch the wire they complete the circuit and get shocked keeping them within the fence.

My question is this: If the fence wire becomes grounded through improper insulation will the battery go dead faster.

I was of the oppinion that when the fence is not grounded the only enery that would be expended is that which would be lost through resistance. And if the wire became grounded there would be a greater loss of energy (much like when you have a grounded wire in your car) and therefore the fencer's battery would go dead faster and the solar cells not being designed to recharge under this strain would not keep up as well.

 

[alehman]

If you think of like an ignition coil in a car, the high voltage is produced when the primary circuit is opened. The primary current draw wouldn't change whether the high voltage winding is open or shorted. I would guess it doesn't make much difference.

 

[itsmoked]

I'm not sure what alehman is saying...

I will say that ABSOLUTELY the current drain will go up if the leakage between the fence wire and the ground increases.

I'm sure a cow bingo specialist will come along and confirm this.

 

[IRstuff]

If the fence gets grounded, the battery won't go dead faster, it'll BE dead.

Such systems would count on the load (cattle) to be relatively high resistance and not drain the battery. Otherwise, the battery would drain on the first cow and there wouldn't be enough juice for the next cow. Since the solar cell area is probably relatively small and there is not always sunlight, the battery must be sized to handle a large number of encounters before needing recharging.

A short, on the other hand, will mostly likely drain the battery pretty quickly.

TTFN

 

[jraef]

Fence chargers use a charging cap to pulse 2-4kV DC into the circuit for about 150msec. The fence is an open loop from the charger, around the perimiter, and terminating without a ground. The animal does provide a high impedance connection to ground which gives them a 6-10mA jolt, but there is so little energy in each pulse that even without the animal for impedance, a grounded wire is really not that important as far as battery drain.

The bigger problem is that all of the fence downstream of the ground connection is now dead. Smarter animals like horses continually test the fence for weaknesses. I used to lose my horses in heavy downpours because of that. Cows are not bright enough most of the time. After 10 or 20 shocks, it eventually sinks into their thick skulls that the wire is hot and they don't go back. Cattle crossings work on the same principal of dumb cows. Once they learn that they can get thier feet stuck in the steel rails, all you need to do is paint stripes in the road to look like rails and they will stay away.

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[MJR2]

The biggest thing I have found with the solar chargers is the battery simply dies. Life for a battery is barely two years. You can get several months from a deep cycle 12V battery with no external charging.

Our cattle know when the charger is on from the clicking noise generated from the pulse circuit. I also think they have figured out how to disconnect the hot lead wire. Collectively they may be smarter than me. Well at least any two of them.

I've gone to 115VAC charger as the solar chargers just don't put out enough. I get about 9.2KV when the fence is well isolated. And that doesn't usually last long.

 

[jraef]

Oh yeah, it's SOLAR, meaning that all night and on cloudy days, there is no recharging of the battery. Duh, I missed that, there were no such things when I used them, the battery was for backup if the power failed and charged by the line power. Can't you put more or bigger batteries on the solar units?

Where did you find cattle that smart? The ones I was around were so affraid of the electric fence that they wouldn't come close to the feed if it was too near the fence, even though we turned it off at feeding so it didn't bite us. I never watched to see how long they would stand there staring at the feed, but I know it was over 2 hours because I would do other chores and watch. I was affraid they would die of starvation so I would move it father away for them.

 

[itsmoked]

They could sense the vile EM field washing over their delicate skin. They stand there becuase they are busy doing the time/exposure/mutation rate calculations in their heads.


Solar panels are getting cheaper all the time(slowly) just get larger ones so the battery makes it to full charge in a few hours of sunlight. With larger panels you can get 'significant' charging even on overcast days.

Look at marine stores for boats they have lots of battery charging solar stuff. West Marine for example.

http://www.westmarine.com/webapp/wc...01&langId=-1&catalogId=10001&productId=232805

http://www.westmarine.com/webapp/wc...001&langId=-1&catalogId=10001&productId=56823

 

[jraef]

Maybe Gary Larson was not joking in all those Far Side cartoons about cattle having hidden abilities then.

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[ccjersey]

If you have ever watched a voltmeter on one of the newer electric fencers as you turn it on,it increases with each pulse up to a steady state range of voltage, IF it is not shorted out much. The more leakage on the fence, the lower peak and minimum voltages become. This can be used to "check the fence" if you don't have time to walk it and really check it out.

I guess it means there would be more power expended if each pulse was applied to the fence at a lower initial voltage.

I had occasion to watch the learning curve of a grown bull regarding a new fence wire. He had become a menace to my children whenever they were in the yard by the house. Seeing them or anyone else on the other side of the fence, he would soon be there threatening and pushing under the net wire fence until we retreated to the house. We installed the electric fence by detailing someone to take a large tractor into the pasture to keep him occupied away from the fence. Once the new wire was in place, he promptly came up and smelled it, twice, and that was that. Very satisfactory outcome for human and bovine alike since he was fast becoming a candidate for hamburger the way he was heading.

I also think Gary was right about those hidden bovine capabilities.

 

[itsmoked]

Man I wish Larson was still working.. Him and the Calvin and Hobbs guy.

 

[RalphChristie]

Well, I am not really contributing to the original question, (sorry jandrewg ) but animals are really intelligent.



Here we use a lot of these electric fences (from a few metres to several hundreds of kilometres long) to:

- keep animals inside (stock farms, game ranches, National Parks, etc)
- keep animals outside [either predators (jackal, lynx, etc.) or herbivores (stock, warthogs, kudu's, etc)]




These fences help a lot, if an animal was shocked once, it learns from the experience. Even big game, like elephants, handles it with respect (except if angered or excited). My dog once touched such a wire, and never did it again. But they quickly realize when such a fence is not switched on.

A warthog is one exception. I have seen if they want to feed on something, they come in, even if a fence is switched on. They approach such a wire with speed and force and they start screaming (like a pig

) 20-50m from the fence until they are inside.

I have also heard (but can't confirm it) that big baboons

throw there young into the wires, and if they are shocked, the big ones quickly jump over.


Was anyone shocked by such a fence? Let me assure you, that is quite a shock!

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[itsmoked]

Now that IS interesting!

 

[wfowfo]

Quote:
" Smarter animals like horses continually test the fence for weaknesses."

I'm speechless.

Personally I think bugs (after they've hit my windshield) are smarter than horses.

More to the point, there is more than one type of fence charger; some that pulse (called weed wackers around here) and ones that stay hot continuously. The continuous ones are much more susceptible to grounds than the pulsing type.

Explain this phenonmenon to me.

My boss showed me how to check an electric fence to see if it was hot. He said take a long stem piece of grass, hold it at one end , and slowly slide it closer to the wire until you felt a tingle. So I tried it, got closer and closer, and never felt a thing. At that point, my boss touched my arm and it knocked the poop out of me. He didn't feel a thing.

What gives? Why would I catch it and he didn't?

P.S.-Obviously, horses are smarter than I am.......

 

[fsmyth]

Shoes.
<als>

 

[alehman]

But why didn't the boss feel anything?

 

[itsmoked]

Shoes.

 

[nostrayvoltage]

Well in fact it is current that causes the shock so insulating shoes would prevent shock.......same problem occurs when an animal is standing on very dry ground.......with a single hot wire fence construction...or if the fencer is inadequately grounded

Back to the original question......seems that everytime the fence is pulsed, all of the stored energy in the capacitor is used up, so the life of the stored battery charge would be the same......the difference is where the energy goes.....

Electrical fencers and their installation is a very interesting topic indeed......

 

[wfowfo]

I know this is off topic, but I'm still wondering.

If shoes were the reason of getting shocked, it still doesn't explain why we didn't both get it. If his shoes were "grounded", the current would have still had to go through me AND through him. It wasn't my shoes since I already had hold of it with no effects.

 

[itsmoked]

You are not being confused by the fact that fences pulse?

Maybe when he touched you, [he being insulated with different shoes](so he wouldn't be shocked) just happened to be when the next pulse came and you are mistakenly relating them. ??