HV Charge for electric fence - Page 1
Forum section: electronics / projects

author: jfsimon
author_rank: Contributor
timestamp: November 06, 2022, 01:54:33 pm
content: Good day,I seek for advises in design of Hornet protection (electric harp style) fence charging circuit,In brief what type of circuit would you recommendAs I didn't find transformer available (searched at Farnell), i assume we need build a customer (here 12/2200V) transformer.The suggestions i had in mind was fully insulated HV side with 150 mJ energy stored in HV cap at 2500 V.As i understand, we should charge 150 mV at 12V capacitor and pulse it over a transformer to charge at HV.I have seen circuits with protection resistor at the output ranging tens of Ohms i believe just for safety reason.I'm not experienced with HV hence either i still consider both consider finalizing and prototyping it or get anoff shelf solution.If some people have experience with such design it would be of help,Thanks & regardsJean-François

author: jonpaul
author_rank: Super Contributor
timestamp: November 06, 2022, 02:03:36 pm
content: Bonjour cher monsieur:Fence charges use induction coils and HV inverters to creat a pulse HV or charge a HV cap.The energy is carefully controlled.Safet of the public requires a consideration.Very difficult to DIY.Think of your personal responsibility if an animal is injured or a person with a heart condition/pacemaker accidently contacts the fence!Strongly suggest to purchase, the solar powered and 12V battery are easily available at garden/farm supply stores.Bon ChanceJon

author: jfsimon
author_rank: Contributor
timestamp: November 06, 2022, 02:15:30 pm
content: Merci, yes i consider both.JF

author: twospoons
author_rank: Frequent Contributor
timestamp: November 06, 2022, 11:29:53 pm
content: I used to work for a company designing fence energisers. There is a lot more to it than just generating a few thousand volts pulse. For safety Istrongly recommendbuying a ready made one, that meets all the standards.

author: jfsimon
author_rank: Contributor
timestamp: November 07, 2022, 08:07:28 am
content: Thank you,I purchased to make it though for lab&test purposes only, hence i haveprobably found the right commercial product for the intended of use andwill do otherwise testing only with diy.RegardsJean-François

author: Hydron
author_rank: Super Contributor
timestamp: November 07, 2022, 01:41:08 pm
content: Quote from: twospoons on November 06, 2022, 11:29:53 pmI second this, have also seen how it's done from the inside while I was a student (probably either at the same place as twospoons, or at another NZ competitor). Concept is fairly simple (normally a bank of caps, a SCR, pulse transformer and shaping network) but the implementation to make it safe, legal and reliable in a farm environment isn't. Note that it doesn't _absolutely_ have to be done with a pulse transformer though:https://patents.google.com/patent/EP1667497A2/en(AFAIK this concept didn't go anywhere in the end).

author: CaptDon
author_rank: Super Contributor
timestamp: November 07, 2022, 02:08:28 pm
content: Here's a blast from the ancient past, Ford Model A ignition coils have a magnetic pole piece sticking out the end and it excites a piece of spring tempered metal with a metal point contact on it to form something similar to a d.c. powered doorbell buzzer. This creates the make/break collapsing magnetic field to create the high voltage spark on the secondary winding. Anyone who has ever played with one of these coils knows they can throw a good one inch spark!! Hillbilly farmers being inventors of ideas from scrap laying around found you can replace the 'buzzer' contact with a hacksaw blade and some added weight at the far end and get a pendulum producing the familiar once-per-second tick....tick.....tick and a fence charge that will take your legs out from under you. I had one of those '50 mile' fence chargers (Store bought) connected to a small 3 acre paddock fence. Since it had very little capacitive loading it could also knock you off your feet! It was no joke when certain fence chargers were known as 'weed burners' which did in many cases lead to 'field fire starters'!! Those electric fences when disconnected from the charger make great ham radio antennas and on the flip side when actively being used as an electric fence will piss off ham radio operators and short wave listeners for about 2 miles in every direction!!!

author: jfsimon
author_rank: Contributor
timestamp: November 07, 2022, 06:12:01 pm
content: Thanks for all interesting infos.I initially had in mind to charge about 140 mJ at 2.5 kV and keep it charged statically (ie passed the charge phase we stop the LV side).Charging the LV cap "ready" for a pulse and wait for HV to discharge.Though that's complicating quite a lot, it's also keeping from unnecessary current draw which would be good given it runs on small battery/solar.For the moment those will remain in works or test field as i mentioned.RegardsJean-François

author: Marco
author_rank: Super Contributor
timestamp: November 08, 2022, 11:13:57 pm
content: Quote from: twospoons on November 06, 2022, 11:29:53 pmThe power to stun a hornet is a little less than to jolt a cow, it also doesn't have to deal with plants partially shorting it out over huge distances. It can be orders of magnitude lower power/danger.

author: twospoons
author_rank: Frequent Contributor
timestamp: November 09, 2022, 04:13:42 am
content: OP is talking about using 140mJ. The smallest energiser we made for stoppingcowson temporary fences (for break feeding) was only 100mJ. And they really hurt if you get your hand on the business end. Hence the words of caution, where mistakes can be deadly. To be fair, that energy level should be reasonably low risk, but you never know who else might read this thread and take it into their head to make something bigger.

author: Marco
author_rank: Super Contributor
timestamp: November 09, 2022, 06:59:07 am
content: How about a flyback driven by a gated square wave of fixed frequency and duty cycle (power limiter) with a resistor on the output (average current limiter) to the capacitor and some TVS in parallel with the capacitor (voltage/energy limiter). Usually a control loop would prevent the TVS from conducting, just a final bit of safety.How much could go wrong with average current limited well below 10 ma?

author: coppercone2
author_rank: Super Contributor
timestamp: November 09, 2022, 07:59:25 am
content: why do I have the feeling that safety critical rugged high voltage equipment is not something you should be working on.your country code = buy ityour not gonna beat the price if you actually want to do it properly with the correct tests and quality assurance practices (i.e. large scale parts testing). You know they might do something like let 100 models run for 1 year before manufacture for sale (vetting) in case there is something hidden going on that can cause a problem (odd parameters of parts that apply at high voltages in bad conditions).Hobby HV circuits = touch safe because they are inside of a protected enclosure. You want touch safe without the enclosure. That's basically a full medical design you know? designed for potential interaction with life forms. You can get buried in standards doing that kind of design. When you are designing it to be touch 'safe', its basically that it HAS to be a medical device class.If its a corporate effort maybe someone can suggest some standard guidelines. For some reason I think it will be way more challenging then typical medical equipment, since you are designing for it to deliver energy correctly, not designing it to not deliver energy ever.

author: Marco
author_rank: Super Contributor
timestamp: November 09, 2022, 04:27:01 pm
content: Those hornet fences seem highly specialized, some single digit Hz energiser is entirely useless for it. Probably electric fly squatter circuits are more appropriate.I'm not sure they are even commercially available, it seems mostly a DIY game by beekepers less concerned with medical designs.

author: Marco
author_rank: Super Contributor
timestamp: November 09, 2022, 06:53:33 pm
content: There also seem to be designs using with almost no stored energy other than in the self capacitance of the wires, they don't really fully explain the electronics but it sounds like a 1000V supply with a 330K output resistor and nothing more.https://onlinelibrary.wiley.com/doi/full/10.1002/ps.7132http://www.oepm.es/pdf/ES/0000/000/01/20/30/ES-1203011_U.pdfPS. not safe, but not more dangerous than the beehive next to it.