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Working with high voltage pulses

Discussion in 'General Electronics Discussion' started by Oldnewbie, Dec 29, 2015.

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  1. Oldnewbie

    Oldnewbie

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    Dec 28, 2015
    Hello all. I am new to electronics and have made it about half way through the Make: Electronics course in the last month or so.

    I have a project in mind and would like to enlist some help in getting me pointed in the right direction. I have an electric fence which is used to keep my cattle fenced in. Occasionally, the voltage in the fence drops for various reasons; i.e.: break in the line, wet grass, bad ground etc. I have a fence tester to check for voltage drop but would like to put something permanent on the end of the line to automatically indicate that the fence requires maintenance. Basically, I want to know how much voltage is going through the fence and in the event of a problem I would like some indication as to the severity of the problem.

    LEDs could be used to indicate the amount of voltage of each pulse, similar to the tester that I have. Or it could be a digital display. The electrifying unit I have puts out pulses up to 7kv. If LEDs were used the voltage could be indicated in increments of 1kv. So if the pulses were at 3.5kv only 3 LEDs would light up. (The 1kv indicator LED, the 2kv indicator LED and the 3kv indicator). In addition, I would like to have a visual warning to indicate a voltage drop. For example; have the unit flash some yellow LEDs to indicate that the voltage has dropped a certain amount and some red LEDs to indicate that there is no more voltage in the line.

    The main problem I am having is how to get the high voltage pulse down to something I can work with.

    Hope this all makes sense. Any help is appreciated.
     
  2. Gryd3

    Gryd3

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    I can tell you what I would personally try... but my experience in higher voltages are limited...
    I'd build a voltage divider to bring the level down to something I could work with.
    Your voltage divider should be a very high resistance to prevent current flow from the fence and to prevent the voltage from sagging on the fence.
    I cannot offer advise on powering something from the fence, and would strongly encourage you to avoid using an external power supply for the 'tester' . This leaves you with the requiring the use of one or more batteries.
    Some very simple logic can be used to create an output when the input drops too low. Simply buy and wire in a 'flashing LED' and you won't need to worry about an oscillator. I would encourage the use of a momentary push button for the additional LEDs to show you the current level though.
    As always, make sure your device is well insulated and never touch the live circuit... but I am assuming you will be following numerous safety steps to ensure you do not shock yourself.
     
  3. cjdelphi

    cjdelphi

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    Thing is, these devices put out high voltage (but next to no current)

    So powering the device is tricky, i'd opt for a small solar panel and a push button to test the voltage..

    Gryd's suggestion of a voltage divider sounds good, depending on the voltage, you could have different LEDs light up (red/bad orange/ok green/good) all you need then is a comparitor or 2 ...

    But i too lack HV experience, but since the current is low, a voltage divider sounds good
     
  4. Oldnewbie

    Oldnewbie

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    Dec 28, 2015
    Wow quick replies! Thanks to both Gryd3 and cjdelphi for the responses. I'm going to do some reading and testing of voltage dividers.
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Could you please provide us with link to the product page?

    Chris
     
  6. GPG

    GPG

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    Sep 18, 2015
  7. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I think this is a first for me. I read the whole entire thesis from start to finish! I save a lot of information that I start reading but never finish. Not this one though.

    While reading this I thought to myself this is exceptionally detailed thesis, especially for a device not targeted at home hobbyist. I further thought "Gee, the only thing missing would be code"! Ha, I found that he included that too!

    Musings: After reading this exceptional thesis it occurred to me that this document should be kept on hand as an exemplary example of what engineering and design of a product can entail. When we get one of these. .

    "Hey, I'm new here and I'm also electronically challenged but I know this will be easy stuff for you guys. I have a new product idea that want to market. I want to hire someone to design it. Oh .. and by the way! I want you to do this for under $200.00".

    EDIT: Oldnewbie, it occurred to me that you may think that some of my sarcasm was pointed at you. Actually it's not. It's just a general observation of some of the requests we get.
    Chris
     
    Last edited: Dec 30, 2015
    Arouse1973 likes this.
  9. Oldnewbie

    Oldnewbie

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    Dec 28, 2015
    CDRIVE .....sarcasm - what sarcasm? The energiser that I have is a Gallagher M400. It is no longer sold but the website for Gallagher is
    http://gallagherelectricfencing.com/collections/ac-energizers They don't have much technical info on their products, surprisingly enough.

    GPG thanks for the info on high voltage dividers. And especially the link to the thesis. I have skimmed through it and will take a closer look in the next day or so. Great stuff!
     
  10. hevans1944

    hevans1944 Hop - AC8NS

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    Another amazing find from New Zealand! Thank you very much, @GPG. If this is typical of the work of post-graduate students at Massey University we could use some more of it here. Very professional, very complete, very well-researched master's thesis paper. Kudos to Glen McGillan.

    BTW, this is material copyrighted by the author for non-commercial private and research use only, so don't head off to Staples and run off copies for your friends. Send them to the download link provided by @GPG instead.
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    OK, so now that Glen McGillan's thesis has given us a clear picture of typical electric fence topology and electrical requirements I scooted over to Ebay to see what the Chinese are marketing. I've made a habit of doing this because the Chinese export explosion has totally changed the advantages of some DIY projects. IE, they can sell many commercially made products cheaper than you can make it yourself.

    So before we proceed check out some of these links. My Ebay search terms were Electric Fence Tester and Electric Fence Monitor. While some of them don't meet the requirements you posted some do and they're very inexpensive. Here's one that's Made In USA

    Chris
     
    hevans1944 likes this.
  12. Oldnewbie

    Oldnewbie

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    Dec 28, 2015
    Chris,

    When I thought of doing this little project my aim was to kill 2 birds with one stone. Firstly, I would make a product that was useful to me and secondly, it would help move me along in my understanding of electronics. I used a similar strategy when I decided to take up welding. The teacher suggested that we do a project which interested us. So I ended up with a log splitter that I use to split around 100 cords of wood a year. It has a log lift which will lift a 1000 lb log, has a 25 ton ram and will split up to 36” in length. However, I digress.

    The project that I envisioned was to build a passive monitor. One that would only alert me if there was a problem detected. The problem that I could see with active monitors is that after a while you may not notice that the monitor is no longer blinking. I do have an inexpensive electric fence tester but it only tells me that there is a problem when I use it (which is usually after I spot a calf in the wrong enclosure).

    Reading the details of Glen McGillan`s thesis made me realize that this project is far too complex for me to undertake with the very limited knowledge that I have. I am going to put this project on hold for a while and do some easier tinkering to increase my knowledge. However, I may very well be spending $35.99 on the Made in USA monitor that you pointed out.Thanks for your input.


    Ben
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    You can also use a string of normal resistors. Typically these are rated for about 200 or so volts, so if you need to drop 7000 volts you'd need at least 35 of them.

    To be safe I'd make a divider out of 100 resistors with the 100th grounded ant the trap between the 99th and 100th. If use resistors (all one value) between 10k and 100k each.

    Google for plans fir making a high voltage probe. Layout and insulation are also very important. Whilst you may only get a kick from an electric fence, your multimeter (if connected incorrectly to the high voltage probe) can be killed.
     
  14. duke37

    duke37

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    The Massey link would not work for me, perhaps the internet stopped up too late last night.

    I have mended a few fencers and was given a Gallager voltmeter to check them.
    I think that using leds is not optimum since they take significant current, however the newer mains fencers seem to have an output impedance of 5kΩ so should be able to manage this.

    I made a variable spark gap to measure voltage with a 6mm bolt with thread of 1mm/turn. I assumed a voltage of 3kV/mm (see Tesla forums). This agreed fairly closely to the Gallagher meter.
    I would have a group of varying gaps, feeding neon indicators which are often use in fencers to monitor output. They should have a resistance in series and in the fencers these are often just standard resistors and do not seem to be anything special. The flash could be detected with a light sensitive device to activate an isolated low voltage circuit or the current pulse could be used. There are pulse transformers to trigger flash tubes, one of these could be used in reverse to give a more reasonable voltage out.

    Perhaps current running into the fence would be a better measure of correct operation.

    Whilst vegetation will affect the voltage, I was asked to repair the fencers mostly due lightning but in one case the printed circuit board came in two pieces, I glued it together and repaired the traces and it worked. A year later it turned up again and I refused to mend it until I was told what had happened which was that the fence had been caught on a plough. I suggested that the connection to the fence should be made with a crock clip.

    Running the fence close to an overhead phone line gives a good method of monitoring the fence with no extra equipment needed. I always know when my brother phones before he says anything.:)
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Duke, your post got me thinking of a totally different approach. Both you and Glen McGillan`s PDF addressed the negative effects of electric fences on telephone lines. As I see it an electric fence is damn near the same as Marconi's Spark Transmitter but lacking the spark. This started me thinking of burying underground UTP that emerges at the end of the fence line and bringing the opposite end up at the house or barn. All sorts of electromagnetic monitoring schemes come to mind. Doubtful this concept will or could work if the feed end of the fence meets (360deg) the end of the fence.

    Since the fence constitutes a single ended dipole antenna of sorts, it's radiation pattern should be max when measured parallel to the fence and weakest off the ends. Admittedly I'm not firing on all cylinders right now but I'm feeling that little spark of genus that comes along at this time every year.

    Oldnewbie, don't get discouraged after reading that PDF. Many of the hurdles addressed in it are not applicable in your case. You don't need data capture speed that is needed with a walk around tester. In your case it isn't going to matter much if you simply divide the high voltage pulses down to a manageable level, rectify and filter it. Then you'll have a DC level to work with. The divider tap output would have to drive a high impedance device like the Gate of a FET.

    BTW, I always feel like a 10 year old when addressing handles. What's your name?

    Chris
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    O-N, I forgot to mention that I'm addicted to Youtube log splitter vids. Some are insanely dangerous but those are found under "Epic Fail"! :eek:

    Chris
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Another thought.. I think we can make the divider-rectifier- filter capable of driving the analog input of an LM3914. The circuit would have to be powered by batteries or mains to LVDC power though.

    Chris
     
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