Electric fence or similar circuit with common ground? - Page 1
Forum section: electronics / projects

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 06:22:29 pm
content: Hi. I'm looking for a product or schematic of an electric fence circuit or similar deterrent with a common ground.Purpose: I'm sometimes in bear country and in some places like Whitney Portal a tiny population of 22 bears cause literally hundreds of thousands of dollars in damage a year. The official regulation of scrubbing a vehicle of all food, cosmetics, etc. is impractical and often doesn't work. I have a 12v solar setup that can indefinitely power something with a reasonable draw and the vehicle has metal fenders all around. The idea is to steak in a ground and electrify the chassis. The problem is the chassis is also the 12v ground. I did obtain and take apart an old commercial 12v electric fence module (with a broken case so it didn't cost much) but there was no common ground (battery is isolated). To use this I would have to somehow provide an isolated 12v source. I considered using an inverter and transformer but there might be feedback to the inverter which could fry it which is a fire hazard.Any suggestions?Edit: I probably threw out that commercial circuit because it didn't fit my needs.

author: janoc
author_rank: Super Contributor
timestamp: March 09, 2021, 06:38:53 pm
content: This sounds like a splendid idea - until some non-bear entity touches your car not knowing that it is electrified - such as a ranger/cop checking it or even a passing tourist. Or some kid. I am pretty sure that the free shock will be appreciated by everyone.Also, high voltage prone to sparking and arcing on and around a car with gasoline in it sounds like a wonderful plan how to set things on fire.I get that bears could be a nuisance but there has to be a less dangerous/stupid way of protecting your vehicle, surely?

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 06:42:58 pm
content: You don't appear to be aware what electric fences are. Hint: this isn't hollywood.They're an irritant used to keep cows in their place. If they caused fires or bodily harm half the planet would currently be engulfed in flames.

author: Medved
author_rank: Contributor
timestamp: March 09, 2021, 06:49:56 pm
content: But the fences manuals are explicitly stating use out of reach of any combustible vapor, in one form of legalese language or other.Plus fences are appropriately marked along their length, with corresponding warning labels, which is what makes them safe in front of liability laws (otherwise their installation is illegal and may bring a lot of liability troubles for the owner). I doubt you may install it on a car, yet still be compliant regarding electrical fence rules...

author: fordem
author_rank: Regular Contributor
timestamp: March 09, 2021, 06:59:41 pm
content: Hmmm, cows, methane, combustible vapor? And yes, I have seen the off visitor to a local dairy farm unwittingly come into contact with an electric fence, better hope whoever comes into contact with your car has a good, strong heart - strong so that it doesn't stop, and good so that he/she doesn't file a suit over it.

author: Medved
author_rank: Contributor
timestamp: March 09, 2021, 07:08:32 pm
content: Quote from: fordem on March 09, 2021, 06:59:41 pmMethane needs certain concentration to be flammable. Cows can not make that, definitely not outdoors. Plus methane is way lighter than air (about half the density), so rises up quite fast, so does not accumulate (unless under well sealed roof). With such high concentration of the "cow exhaust gas" the cows would be long dead from H2S (and other components) poisoning, if it would be allowed to accumulate that much...So no, cows won't create any explosive gas hazard, don't worry.But you may have a small fuel leak, forming a puddle with saturated gasoline vapor on top of it, definitely within the explosion concentration range...

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 07:31:37 pm
content: Good gravy, does anyone feel like answering the question instead of coming up with movie scene ideas for Michael Bay?

author: Medved
author_rank: Contributor
timestamp: March 09, 2021, 07:38:10 pm
content: No, because it implies liability if anything bad happens...If not the legal one, for sure the conscience one...

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 07:39:40 pm
content: I've installed an electric fence before and you're being ridiculous

author: tautech
author_rank: Super Contributor
timestamp: March 09, 2021, 07:59:34 pm
content: I wouldn't connect the electric fence hot to a vehicle without the risk of damaging the vehicle electronics.Better to use a few electric fence standards and string a fence around the vehicle IMHO.Unless you are happy to walk home...............

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 09:07:43 pm
content: I do plan on hooking up my $2000 diagnostic reader and making sure there is no feedback THANK YOU FOR YOUR CONCERNMaybe you can all chime in on what color to paint the vehicle.

author: tautech
author_rank: Super Contributor
timestamp: March 09, 2021, 09:18:06 pm
content: Quote from: ball on March 09, 2021, 09:07:43 pmYou say you've worked with electric fences, well so have I !10kV 40 Joule units that will sit you right on your arse !Please don't dismiss my concerns about your intended use of a fence unit that presents great risk of damaging modern vehicle electronics.......unless you're driving a Model T in which case you'll be safe.

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 10:03:27 pm
content: Are 10kv fences apropos to this thread? If so, please enlighten me.Edit: Used to have 70kv ignition system in a different vehicle that would cause a bit of feedback. Unless you've actually fried your car's electronics maybe we can put those concerns aside

author: janoc
author_rank: Super Contributor
timestamp: March 09, 2021, 10:27:51 pm
content: Quote from: ball on March 09, 2021, 06:42:58 pmI know exactly what an electric fence is but you don't seem to be aware that there is one heck of a difference between a 500 kilo cow brushing along a wire (and getting a shock) and a 30 kilo kid accidentally getting it.I don't know how about in your country but this type of "self-help" would get you in a pretty hot water with the law the moment someone gets hurt. I hope you are going to properly placard your car warning everyone about your "bear repelent", the same as electric fences must be marked and installed.Quote from: ball on March 09, 2021, 07:31:37 pmBecause nobody is as stupid as to expose themselves to a potential legal liability if they tell you how to do this, you do it and then someone will inevitably get hurt sooner or later?And with your attitude (and evident level of knowledge) you wouldn't listen anyway.

author: janoc
author_rank: Super Contributor
timestamp: March 09, 2021, 10:34:52 pm
content: Quote from: ball on March 09, 2021, 09:07:43 pmGood, so you will fry not only your car but your $2000 "reader" too.Hint, do you really think that a gadget connected to the CAN bus can actually tell you if there is a microsecond spike of a few kilovolts due to some parasitic inductive or capacitive coupling or some insulation breaking down (such as a wet tire)? Good luck with that one.

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 10:36:35 pm
content: If there was only one spike maybe not, but if it's recurring that gets picked up all the time.

author: tautech
author_rank: Super Contributor
timestamp: March 09, 2021, 10:47:41 pm
content: Quote from: ball on March 09, 2021, 10:03:27 pmSolar power 12V fence units with a legally permitted 10kV output are common as mud here in NZ....the home of electric fences where forefathers to Gallagher electronics developed their first fences in the '30's.https://www.gallagher.com/about-us/the-gallagher-story

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: March 09, 2021, 11:09:33 pm
content: Quote from: ball on March 09, 2021, 06:22:29 pmReally? How hard can that be?

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 11:35:37 pm
content: Quote from: JohnnyMalaria on March 09, 2021, 11:09:33 pmIf it's a camper damn near impossible. Previous vehicle had pancake syrup soaked in the carpet. Good lock ever getting that shit out. Bears have the most sensitive olfactory system in the animal kingdom. You think your vehicle is clear of all cosmetics, but a bear smells that toothpaste smudge from two years back that will never be cleaned. It's never too much trouble for them to check, either. they're built to rip rocks out of the ground to eat a moth. Opening a car is as simple as pulling down on the door with one paw.

author: TimFox
author_rank: Super Contributor
timestamp: March 09, 2021, 11:42:11 pm
content: Building codes recommend handles instead of knobs on doors, which is good for those of us of advanced years. It didn’t take bears long to figure them out.

author: ball
author_rank: Contributor
timestamp: March 09, 2021, 11:45:43 pm
content: My bear cans can't even be used anymore as they figured out how to open them, but the way they open doors is to simply crush them. They put a paw on the top above the window and effortlessly rip it down. Then they rip open your seat to find that curious smell which was that 2yr old toothpaste smudge.

author: fordem
author_rank: Regular Contributor
timestamp: March 10, 2021, 02:39:54 am
content: Quote from: Medved on March 09, 2021, 07:08:32 pmEver lit a fart? It's not my intention to imply that you're a cow, but, I do believe that it works just as well with cows as it does humans, and probably better given the relative sizes of the animal, their stomachs, etc.

author: CaptDon
author_rank: Super Contributor
timestamp: March 10, 2021, 05:46:51 pm
content: There is a way to do what you want to do. Put the 12vdc fence charger unit on the car with the ground of the unit grounded to the car, it should also be the same as the negative input lead, zero resistance but check first. THEN take the high tension lead through some good insulated wire like perhaps spark plug wire and connect the high tension lead to mother earth with a good grounding rod or similar. Look at it this way, your fence charger would put a high positive voltage spike into the fence (Actually it is a ringing inductive kick pulse, A.C. by nature) and it this instance it would attempt to make mother earth positive but in reality the car shifts to a high negative node with respect to mother earth. The problem is, how to de-activate the system before you climb aboard?? There may be long term electrolysis effects on the car. To deter a bear you better be up in the 'WEED BURNER' catagory of fence charger!!!! A moderate jolt of discomfort will only piss off the bear, you need to knock him/her down!!! We made some 'killer' so to speak fence chargers out of Model-T ignition coils and replaced the 'buzzer' with a weighted hacksaw blade as the interrupter. Model-T coils were designed for 6 volts and throw a 1.5" arc. You should see what they can do at 12vdc!!! They tend to internally arc and burn out when presented with no load however.

author: tautech
author_rank: Super Contributor
timestamp: March 10, 2021, 05:53:16 pm
content: The carbon content in modern tires can also become a problem with high energy electric fences..IMHO regardless of how the fence outputs are referenced risk of damage to the vehicle control systems is high.

author: CaptDon
author_rank: Super Contributor
timestamp: March 10, 2021, 05:56:25 pm
content: I found that neon/mercury tube lighting transformers make a great deterrent to the theft of 4 wheelers!!! Not many thieves really tend to hang around long when 45KV at 10ma is reaching out to touch them!! That is the 'constant duty' rating of the transformer, they can do a lot more under load!!! Anyway, you then run into a problem of where to put the bodies!!!Also oil-burner ignitor transformers are great!!!!! You still run into the dead body problem however.

author: TimFox
author_rank: Super Contributor
timestamp: March 10, 2021, 06:09:41 pm
content: The law in the United States generally does not permit “mantraps”, q.v., even on ones own property.

author: ball
author_rank: Contributor
timestamp: March 10, 2021, 07:37:31 pm
content: I took apart one fence energizer and the input and output didn't have a common ground. I checked another with an ohm meter and it did, but only a 4v battery.

author: CaptDon
author_rank: Super Contributor
timestamp: March 10, 2021, 08:57:06 pm
content: No man traps, hehehehe, well there goes my idea about the shotgun with a string attached to the shed door and the sign "Door unlocked, many expensive items inside". Aw shucks. And I thought I found a patented way to fix our neighbor-'hoods'.

author: ball
author_rank: Contributor
timestamp: March 10, 2021, 09:06:31 pm
content: Bears can't read, and a lot of thieves probably can't either. BTW I'm so glad I came to eevblog for legal advice. Surely all the best lawyers are also electronic engineers.

author: tautech
author_rank: Super Contributor
timestamp: March 10, 2021, 09:31:10 pm
content: No need be snarky when warnings of an electric fence operating in areas accessible to the public are mandatory in most places and to electrify a vehicle would require 4 signs to comply.A mains fence installation I did a few years back to deter thieves from a large strawberry farm required warning signs every 50m.

author: ball
author_rank: Contributor
timestamp: March 10, 2021, 09:33:27 pm
content: What makes you think 4 signs is a hardship? I don't.

author: tautech
author_rank: Super Contributor
timestamp: March 10, 2021, 09:39:11 pm
content: Quote from: ball on March 10, 2021, 09:33:27 pm

author: geggi1
author_rank: Frequent Contributor
timestamp: March 11, 2021, 11:29:23 am
content: I would just go for a solar powered electric fence and 4 to 8 fiberglass posts.Its a quick to set up and will not interfere with the car electrics in any way.You will probably also need some signs but this can probably be bought at the farmsupply where you would get the fence and posts.

author: CaptDon
author_rank: Super Contributor
timestamp: March 11, 2021, 02:36:18 pm
content: Many years ago I owned a horse farm in the states. It had a lake and pastures with fences and lots and lots of No Trespassing signs. I was required by the mortgage lender and the homeowners insurance policy to carry an additional liability policy because I owned an 'Attractive Nuisance' and someone could drown or get kicked by a horse. I had a decorative split rail fence as well as wire 'horse fencing' on T-posts inside the split rail fencing. A trespasser would have to go through one fence and over another that included a hot wire. And the insurance company said "it doesn't matter, kids can't read". I guess we need an army of 6 year olds to storm area 51 with recon cameras???

author: ball
author_rank: Contributor
timestamp: March 12, 2021, 05:31:35 am
content: Sounds like you didn't really own it

author: CaptDon
author_rank: Super Contributor
timestamp: March 12, 2021, 02:20:13 pm
content: I actually owned a much bigger share of it than the bank did! With the fact that you folks can be evicted off your own property and your property sheriff sale'd out from under you for failure to pay 'property taxes' does anyone really 'own' their property?

author: ball
author_rank: Contributor
timestamp: March 12, 2021, 03:11:13 pm
content: If you have the allodial title, yes. If not, all you have is real estate which is permission by the land owner (real is royal in latin) to build a house on it. You're an occupant, not the owner, which is typically an incorporated municipality.