Electric fence - Page 1
Forum section: electronics / general

author: PlainName
author_rank: Super Contributor
timestamp: May 21, 2024, 10:18:01 pm
content: Just getting around to acquire an energiser and a bit puzzled by the spec. Typically it says a it's good for a single wire of 8km or multi-strand (that is, two) of 3km. I would have thought that a typical fence with two runs would have them in parallel rather than series, so the length would be 8km for one or two runs.What am I missing? Is it normal to have the strands in series? Seems a bit daft to me! Or is there something else in play?https://www.electricfence-online.co.uk/pulsara-pc1300-hybrid-energiser-12v-230v.html

author: thm_w
author_rank: Super Contributor
timestamp: May 21, 2024, 10:45:31 pm
content: Here is the actual spec, which doesn't match what you wrote:QuoteFrom what I see- Two wire means a ground and hot wire- Multi-wire could be 3 or more hot/ground pairs, supplied in parallel. So I don't know how the 0.5km number is calculated.

author: PlainName
author_rank: Super Contributor
timestamp: May 21, 2024, 11:05:13 pm
content: Yeah, depends how you read it. The features bit says 7km (must've been thinking of output when I wrotewhich I assumed would be single wire. Lower down it says two wire, but then a bit lower it is 'multi-wire' at 0.5km.I just happened to pick this one as the one I was looking at, but they all seem to have a similar reduction in length for multi-strands. A more upmarket one, theGallaher M550says 110 (presumed km) for single wire, 35 for two wire and 9 for multi-wire.

author: thm_w
author_rank: Super Contributor
timestamp: May 22, 2024, 12:06:01 am
content: The M550 maybe makes a bit more sense, 25km rating with one pair, divide that by 3 pairs gives 8.3km which is close to the 9km multi-pair rating. Assuming its 3 pairs because they write (3) for multipair.There are probably so many factors they just give these ballpark numbers. If you care you can probably go and measure the voltage upon install.Quotehttps://fieldcropnews.com/2018/05/selecting-an-energizer-for-your-electric-fence/https://www.pakton.com.au/terminology%20and%20units1.php

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 22, 2024, 01:03:00 am
content: There seems to be a dependence on vegetation, but as in many devices they aren't consistent on conditions and definition.

author: johansen
author_rank: Super Contributor
timestamp: May 22, 2024, 01:12:15 am
content: My guess is capacitive loading limits how strong the shock is.Just for fun my sister held onto the neighbors fence wire for more than a few seconds.. he had chickens not steer...You need something strong enough to burn through the natural growth rate of the grass while also being strong enough to deter the animals. Hence the length limit

author: PlainName
author_rank: Super Contributor
timestamp: May 22, 2024, 09:03:48 am
content: QuoteAh! Could be. And/or leakage since we're talking 8kV or so.

author: twospoons
author_rank: Frequent Contributor
timestamp: May 22, 2024, 10:03:08 pm
content: Having worked for an electric fence co I can say the fence length quoted is largely marketing BS. But marketing guys like big numbers they can stick on the outside of the box, so thats what you get. The 36J unit was marketed as supporting something like 150km of wire, but if you work it out you'd be down to about 500V at the end of a steel wire that long - not particularly effective. Its a stupid number to use, but I guess its easier to comprehend than Joules for your average farmer.What really matters is the total load (fence capacitance and leakage) and the resistance at the far end of the fence. So you want clean insulators, multiple hot wires, no foliage contact, and good ground stakes (or alternating hot and ground wires ). More energy = handles more fence load and still retains effective voltage levels. Usual target is >5kV to get through the fur and into the animal.

author: PlainName
author_rank: Super Contributor
timestamp: May 22, 2024, 10:34:58 pm
content: Thanks, I realise the specific figures are marketing best case, it was just the series/parallel apparent discrepancy that caught my eye.QuoteAh, hadn't considered that but perhaps it might make sense for our setup. Something more to think about

author: rstofer
author_rank: Super Contributor
timestamp: May 24, 2024, 01:33:36 am
content: Maybe Google can help:https://extension.umaine.edu/livestock/pasture-course/lesson-3/electric-fence-design/

author: PlainName
author_rank: Super Contributor
timestamp: May 24, 2024, 07:11:37 am
content: Quote from: rstofer on May 24, 2024, 01:33:36 amOr maybe not:QuoteWhy would you want to do that? It seems perverse to wire them in series.

author: IanB
author_rank: Super Contributor
timestamp: May 24, 2024, 08:44:40 am
content: Quote from: PlainName on May 24, 2024, 07:11:37 amI don't think it said anything about wiring in series. It just said that 1 mile times four strands per mile = 4 miles total strand length, which is plain arithmetic.Basically, all fences have leakage, so the more wire length you have, the more leakage you have. If you have no leakage you could in principle have an unlimited fence length. A given energizer can only support a certain amount of leakage before it becomes ineffective.

author: tautech
author_rank: Super Contributor
timestamp: May 24, 2024, 08:58:54 am
content: Quote from: PlainName on May 24, 2024, 07:11:37 amLivestock class, leakage, vegetation, ground conductivity and wire gaugealldictate what is possible.In a prolific growth climate like here in northern NZ there are tradeoffs we make from experience to use with electric fence design and construction along with the livestock class needing control.Here we have some runs of 3.2mm (8g) out to breakout points where wires then run out as 2.5mm feedlines on pre-existing fence lines and/or to 2 or 3 wire fences with all wires hot !We target ~4kV furthest from the unit for reliable control of cattle and our longest runs are approaching 2km.Most NZ electric fence installations use earth/ground return whereas in dry climates a fence for larger stock might only have 3 wires, 2 hot and the middle the ground return. The issue with this layout is stock might already have their head and neck well through before contacting the 2 wires necessary to get a jolt.I know from decades of livestock farming that a zap at this point normally propels an animal forward as their natural reaction is to run from danger, far more than engaging reverse gear.As energiser have become more powerful (ours is 40J) their earth fields require more care and several long galv ground pegs to adequately transfer the current to the subsoils and the longer/deeper they go the better.For some decades my preference has been to use a full 6m/20ft length of 20mm galv pipe, quite easily installed full depth by hand with a water supply on the top end and using an up/down motion for a water hammer effect.When down this deep the soils are very moist which much improves conduction.

author: PlainName
author_rank: Super Contributor
timestamp: May 24, 2024, 12:10:49 pm
content: Quote from: IanB on May 24, 2024, 08:44:40 amI can see that leakage/capacitance can complicate what would otherwise be a relatively simple matter, but I don't think it changes the topology. We would normally consider resistance to be the limiting factor for length, so whereas 4 miles of wire would have much the same leakage however it's set up, 4 miles in series is quite different to 4 x 1 mile in parallel.Further, in parallel a break won't turn it off downwind of the break, whereas in series it will. Also, in parallel any point on the wire will be closer to power than ~7/8 of the points in the serial setup.So I think it's fair to assume that when they say 4 strands of a 1 mile fence comes to 4 miles they are talking series. Otherwise it would be 2 miles, or 3 miles at worst. And my question then is why series? They must be something important that dictates that (because it seems to be not just common but the default), and even allowing for grass and animals and similar - actually,because ofall that - parallel would seem to be the sensible topology.Except... if you've got undergrowth that is now overgrowth and shorting the bottom wire, it might make sense to have that run in series from the far end, so that it's shorting the very end of the chain rather than putting a load near the start. But, surely, in that case it would make more sense to just clear the fried grass instead.So, as I say, I am missing something...

author: tautech
author_rank: Super Contributor
timestamp: May 24, 2024, 12:22:50 pm
content: Quote from: PlainName on May 24, 2024, 12:10:49 pmYep, exactly how I configure them when I know undergrowth is to be a problem.Yet this is one of the advantages of the bigger energisers, the excess power to smartly burn off any plant growth that comes in contact with wire and potentially reducing fence maintenance.In another life I did fencing contracting for some 10 years.......

author: PlainName
author_rank: Super Contributor
timestamp: May 24, 2024, 01:48:00 pm
content: OK, thanks. I'll add another two 0s to our joule requirements

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 24, 2024, 01:55:29 pm
content: I wonder if it might be possible to occasionally switch the fence over to a neon sign transformer or something for a minute or so to burn away the weed growth.

author: tautech
author_rank: Super Contributor
timestamp: May 24, 2024, 02:09:27 pm
content: Quote from: NiHaoMike on May 24, 2024, 01:55:29 pmAnd risk life or limb ?The fact that it's illegal too.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 24, 2024, 07:38:03 pm
content: Burning away vegetation has its own risks. Depending on location and time of year you may end up in the news as the one who started "The Fire".

author: tautech
author_rank: Super Contributor
timestamp: May 24, 2024, 11:12:19 pm
content: Quote from: CatalinaWOW on May 24, 2024, 07:38:03 pmThe time honored method to test if a fence was live was a piece of green grass held by hand and see if the fence provided a tingle to the the tester/holder.The continued pulses inhibit plant growth and brown off the vegetation to a point where it is much less conductive.No sparks to initiate fire are part of the process otherwise electric fences would have fallen from favour decades ago.The much higher risk of fire is from lightning.Let's explore this further, in an earth return fence where the ground wire is connected to the energiser, any sloppy design build not being of a proper permanent build could indeed raise a spark when the hot and ground/earth wires come together when fixtures fail and with the large energisers the continual spark erosion will in time erode through smaller diameter wire.This also presents some risk for outrigger wires on existing fences when non-permanent/sloppy installations exist.When existing fences use a barbed wires there is also some risk of 2 wires hooking together and current flowing into other wires not having insulator fixtures on fence posts.In some areas concrete posts are used and of course they are quite conductive as they are also steel reinforced and as they are embedded 2' deep into the more conductive subsoils.This can be a real issue when ppl climb electric fortified existing fences and also when larger wild fowl that can't pass through a fence might fly over it to pause on the top wire and weight it down to hook onto a barb wire.We've had this problem with freerange turkeys and overcome it with more careful placement of hot wires, more supports and higher wire tensions/strain.

author: Andy Chee
author_rank: Super Contributor
timestamp: May 25, 2024, 02:10:18 am
content: I have nothing technical to contribute

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 25, 2024, 03:45:38 am
content: Quote from: tautech on May 24, 2024, 02:09:27 pmDunno. I would ask Boeing's executives about that.

author: PlainName
author_rank: Super Contributor
timestamp: May 25, 2024, 09:20:52 am
content: Quote from: Andy Chee on May 25, 2024, 02:10:18 amOn the contrary, saved me finding out the hard way

author: twospoons
author_rank: Frequent Contributor
timestamp: May 30, 2024, 01:55:13 am
content: A strong enough fence becomes self-mowing - blades of grass touching the fence will get killed off. From memory this works for energisers of 18J or more. But you need to start with short grass!As for parallel vs series: an electric fence is a high-voltage, low(ish) current device so capacitance/leakage matters at least as much as resistance. So total length still matters whether series or parallel - capacitance and leakage are the same in either case, but fence resilience and resistance are better with parallel wires.eg 1km of 2mm diameter wire, 0.5m above ground, has a capacitance of roughly 9nF. It takes almost half a joule to charge this to 10kV.

author: PlainName
author_rank: Super Contributor
timestamp: May 30, 2024, 08:02:54 am
content: QuoteThat's a good way to put it, thanks

author: tautech
author_rank: Super Contributor
timestamp: May 30, 2024, 09:19:48 am
content: Quote from: twospoons on May 30, 2024, 01:55:13 amWhich is the max for battery powered energisers.Mains energisers are not permitted to create voltages to 10kV.

author: Marco
author_rank: Super Contributor
timestamp: May 30, 2024, 10:09:03 am
content: Are electric fences all lossy transformer based or do some also charge/discharge them through an inductor with energy recovery?

author: tautech
author_rank: Super Contributor
timestamp: May 30, 2024, 11:22:15 am
content: Quote from: Marco on May 30, 2024, 10:09:03 amTypically mains energisers are ~20x step up laminated transformers fed rectified mains via 900V rated pulse grade caps with 3ms pulses.Big energisers draw some 40W but many are less.

author: Marco
author_rank: Super Contributor
timestamp: May 30, 2024, 05:49:22 pm
content: Quote from: tautech on May 30, 2024, 11:22:15 amAbsent weeds and animals, most of the energy seems to be heating up the transformer.

author: twospoons
author_rank: Frequent Contributor
timestamp: May 30, 2024, 10:00:40 pm
content: Quote from: tautech on May 30, 2024, 09:19:48 amIts more of a practical limit than a legal one. Beyond 10kV insulating the fence wires becomes problematic. When I was designing these things all that mattered was adhering to the current vs pulse length limits. Mains vs battery is not a concern re output voltage. The only difference was a requirement for isolation, which was 30kV (from memory). And we did have a mains energiser that put out just shy of 10kV.Quote from: Marco on May 30, 2024, 10:09:03 amThe transformers are not 'lossy' as such, just that there's nowhere else for the energy to go if there's no load on the fence. Energy recovery is not allowed as it would put the energiser back into a state where it could deliver another pulse too early - the upper limit is one pulse per second. In the big energiser I designed the pulse energy wasn't fixed - it was kept at a lower level to reduce heating, and only ramped up when the fence came under load.

author: tautech
author_rank: Super Contributor
timestamp: May 30, 2024, 10:03:17 pm
content: Quote from: Marco on May 30, 2024, 05:49:22 pmWith a 3ms pulse ?Here, almost all electric fences are ground return so a pulse into an open circuit hardly presents a significant load to heat anything up, except anything that touches it !I'm not aware of any vented energisers which indicates there is little or no heating in energiser circuits.

author: tautech
author_rank: Super Contributor
timestamp: May 30, 2024, 10:10:20 pm
content: Quote from: twospoons on May 30, 2024, 10:00:40 pmFor whom may I ask ?It's some 40 years since we installed a now quite small Gallagher energiser and over subsequent years asked far to much from it, as like spider webs, fence systems continue to grow.I do remember 11kV overland lines breaking and falling onto a feed line some 2km from the energiser which turned all the traces on the output PCB into fuses.Some cleanup and bodge wires fitted to replace the vaporized traces and it went on to give some additional years of service until deemed too small to do what we asked of it.

author: twospoons
author_rank: Frequent Contributor
timestamp: May 30, 2024, 10:19:09 pm
content: I was working for Staffix, Gallagher's main competition. Later they were bought out by Trutest. Staffix had a rather nice semi-resonant drive circuit that created a very tidy half-sine pulse on the output. Farmers seemed to like them at Fielddays - usual comment was they felt "hotter". I wasn't brave enough to try, considering even the little 0.1J strip grazers could hit pretty hard.Quote from: tautech on May 30, 2024, 10:10:20 pmHa! You should see the result of a lightening strike - a box full of charred lumps and nice copper plating on the inside of the plastic case.And the transformers do get hot. All the stored energy has to go somewhere on each pulse - and it ends up in the tfr primary if theres no load.

author: Marco
author_rank: Super Contributor
timestamp: May 30, 2024, 10:37:22 pm
content: Quote from: tautech on May 30, 2024, 10:03:17 pmWhere is the power going then? Leakage? EM? The resistance of the wire doesn't matter much AFAICS.

author: twospoons
author_rank: Frequent Contributor
timestamp: May 30, 2024, 11:03:13 pm
content: Venting isn't necessary. The casing is large enough to dump 20 to 30W without the internals getting cooked. An 18J energiser is typically storing around 25J, so at one pulse per second thats ~25W going into the case when not loaded. Its not a lot in a big box.

author: tautech
author_rank: Super Contributor
timestamp: May 30, 2024, 11:28:32 pm
content: Quote from: twospoons on May 30, 2024, 10:19:09 pmAh yes, a trade name now consigned to NZ history. We had a Staffix energiser some years back but would hardly call them main competition to Gallagher which IMO is PEL....at least in the larger mains powered energisers we use.

author: twospoons
author_rank: Frequent Contributor
timestamp: May 30, 2024, 11:40:32 pm
content: PEL got bought up by Trutest at the same time Stafix did. Stafix branded energisers are still being sold by RD1, so the brand is not gone. Looks like the case design hasn't changed much in 25 years.

author: tautech
author_rank: Super Contributor
timestamp: May 31, 2024, 12:08:35 am
content: Quote from: twospoons on May 30, 2024, 11:40:32 pmYes, the Trutest group is certainly good competition to Gallagher....sorta forgot who is now owned by who.Over the years we have had products from all of them and our current energiser was the 2nd largest from PEL when we got it a few years back.We had the option to get the remote control for it but our layout stems from the days when such features were not available and has many pre-existing branch switches to simply isolate fence sections for fault finding and/or repairs.For our switches we use old powerco pole fuses, the now rarer 1/4 turn glazed ceramic types. These don't give shocks in bad weather when wet like the flimsy commercial types.Some years back I did some research into replacing aged pulse grade caps to give weak energisers a new lease on life and quickly found 900V ~40+uF pulse grade caps are a speciality product and IIRC a crowd in Rotorua was one of the main manufacturers but the cost.....Now I have a selection of old energisers primarily for a small stock of their better pulse grade caps which I should really harvest and store and get rid of the old electronics.....then I should also harvest their SCR's but where do I stop !

author: tautech
author_rank: Super Contributor
timestamp: May 31, 2024, 12:11:10 am
content: Quick question if I may twospoons; totally dead energisers, typical failure points ?

author: twospoons
author_rank: Frequent Contributor
timestamp: May 31, 2024, 01:42:53 am
content: Back when I was doing repairs it was usually the diodes across the storage caps that blew - the ones that prevent reverse charging. There was a bit of a design flaw there, using two diodes in parallel. They would fail short and stop the caps from charging. Second most common was the control board getting zapped by a minor lightning flash over on earlier models that didn't have an internal diverter board to send that spark to ground. This was only the Stafix units. We didn't fix anyone else's product.I seem to recall we were using 15uF and 20uF 1200V film caps from Plessy. Their pulse rating was ... dubious, as I found out after destroying a bunch after a week running in a prototype. After talking to them about what we were doing they quoted an I2t rating that was half what was on their datasheet. I guess a 10ms pulse is not in the same league as a 100us pulse with 10x the current.

author: tautech
author_rank: Super Contributor
timestamp: May 31, 2024, 03:35:35 am
content: Thanks, not seen much in the way of diodes across those pulse caps but drags out an old unit that certainly does have the odd diode on a PCB that presses down onto a string of caps with 6mm press terminals and a total of 6 in this one, all 900V 30uF Ducon from OZ.Plessey caps are certainly the more common, also from Aussie.

author: twospoons
author_rank: Frequent Contributor
timestamp: May 31, 2024, 04:13:08 am
content: Internally the Stafix energisers looked like this:C2 is half the size of C1, D1 prevents reverse charging of C1, and D2 was to clamp the primary to prevent ringing and create the half sine pulse.D1 was a weak point - the diodes were a bit underrated for the job, and would sometimes explode just after being replaced.

author: Marco
author_rank: Super Contributor
timestamp: May 31, 2024, 09:16:39 am
content: Quote from: twospoons on May 30, 2024, 10:00:40 pmYou can feed it back to supply rather than the discharge capacitor.

author: PlainName
author_rank: Super Contributor
timestamp: June 09, 2024, 12:03:58 pm
content: Related, I am thinking about making a kind of tester for the fence - a light which indicates correct activity (at the fence) and/or a WiFi broadcast that it's not working now.I acquired aHotline testerwhich I've verified does actually do what it says it does, and that shows the approach I would like to take. But how does it work? I know I could just take it apart but the theory of operation would be more useful than trying to figure out a specific implementation...

author: twospoons
author_rank: Frequent Contributor
timestamp: June 10, 2024, 04:10:01 am
content: Most likely a capacitive divider, using the users hand as the ground end. Then you have a little MCU to measure the divided down pulse and drive the LEDs. Its only likely reading to 10% precision (1kv out of 10kV), since thats all you really need for a fence.

author: PlainName
author_rank: Super Contributor
timestamp: June 10, 2024, 07:41:53 am
content: 10% precision would be more than good enough for me.AFAIK, holding it between two fingers doesn't make any different to grabbing it as shown, which I would have thought would affect the capacitance. Since it's a pulse, could there be a decent capacitor on board, behind a low-pass filter, that acts as 0V (rather than ground)?Hmmm. I can feel some microcap usage coming on

author: Marco
author_rank: Super Contributor
timestamp: June 11, 2024, 09:59:26 pm
content: Looking at a repair video I don't see any grounding pad from the button, so it seems to rely on the capacitance from the PCB ground plane to your hand. With a resistor divider to the ground plane from the look of it.

author: PlainName
author_rank: Super Contributor
timestamp: June 12, 2024, 07:51:58 am
content: Ah! Couldn't find a teardown originally, but since you mention a video I made an extra effort knowing it exists and found it

author: Marco
author_rank: Super Contributor
timestamp: June 12, 2024, 04:51:01 pm
content: It has a micro, it might actually be far smarter than we are assuming. If you know the pulse waveform (which they do if used with their fence energiser) then you can determine the parasitic capacitance to ground with a bit of math from the shape of the measured waveform (the RC network low pass filters it). Once you know the capacitance, you can determine the pulse voltage from the amplitude.

author: PlainName
author_rank: Super Contributor
timestamp: June 12, 2024, 06:35:36 pm
content: It's been accurate (within the 1kV steps) for two completely different energisers I've tried, one 8.5kV and t'other 10.5kV, neither from a company related to it. I will have it apart this weekend to take a closer look

author: Marco
author_rank: Super Contributor
timestamp: June 12, 2024, 06:41:40 pm
content: If you can make the RC time large enough you can just treat the pulse as a dirac pulse and it works even when the pulse changes a bit. Or they could measure two pulses with two different resistors, but the large resistors seem to be in series.What's the value of those large resistors? It's hard to read the colours from the video.PS. maybe they switch an extra small value capacitor in series with the ground plane to get two different measurements with two unknowns from two pulses? (ground plane parasitic capacitance to earth and pulse amplitude.)

author: PlainName
author_rank: Super Contributor
timestamp: June 12, 2024, 08:06:08 pm
content: QuoteI'll let you know at the weekend

author: Marco
author_rank: Super Contributor
timestamp: June 13, 2024, 08:45:20 pm
content: Here's a patent for a different type, they make the handle conductive so they can use the body capacitance as a decent ground relative to the capacitance of their capacitive divider (ie. they make the divider << 100 pf).https://patents.google.com/patent/US9829515B1/enThough that still doesn't explain how the hotline one works. AFAICS the capacitance to ground will be significantly smaller and less predictable, making everything harder.PS. I guess I'm making it harder than it needs to be, I guess it's just a resistive divider and a peak detector, treating the ground plane stray capacitance as a very temporary earth. I was thinking all the parasitic capacitances of the components would mess it up, but I'm probably overthinking it.PPS. works well enough in simulation as long as capacitance to ground is more than a couple pf and the capacitance across the top resistor is small enough.

author: PlainName
author_rank: Super Contributor
timestamp: June 13, 2024, 09:34:56 pm
content: QuoteThat's what I would guess too, and how I would look at doing this. I have an advantage in that I can use actual ground (since it would be an automated monitor without a user holding it), but I would still like it capacitively coupled.

author: PlainName
author_rank: Super Contributor
timestamp: June 14, 2024, 07:42:52 pm
content: Photos attached - they are big for clarity.There isn't a decent ground plane on this, and just to make sure I operated it using plastic tweezers so my hand was relatively distant. There was not discernible difference to normal operation, so I don't think the user is part of it.Components around the hot end, rounded to nearest E24 value:R810MR910MR10510KR117.5KR210MR510MR54470KC23.6uFC41nF

author: Marco
author_rank: Super Contributor
timestamp: June 14, 2024, 11:09:03 pm
content: "C2 3.6uF"Doubt

author: PlainName
author_rank: Super Contributor
timestamp: June 15, 2024, 11:51:10 am
content: Yeah, but that's what it measured (albeit in-circuit). I'll take another look