Electric Fence Circuit Operation

Discussion in 'General Electronics Chat' started by NM2008, Aug 2, 2011.

  1. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Hi there,

    I aquired this electric fence unit as it was no longer sufficient to supply the farm in which it came from.
    It is a moblie unit which operates from a 9v 90Ah battery.

    The unit itself sells under the name of ELEPHANT MOBILE and is built by Ing.Fa GRAND A/S. Made in Denmark.

    I wanted to learn more about the operation of these circuits, so I decided to follow the circuit out.

    The IC in the photos is an NE555 set in astable mode and gives pulse every 1.5 seconds.
    There are two, physically large 4.7μf capacitors on the board.


    I am having trouble determining what the grey component on the board beside one of the capacitors is? On the underside of the board it has six terminals. There are no markings or codes on this component.There is a potentiomter in series with positive and one of the terminals from this component
    (3rd Photo)

    In the first photo (top left corner, on/off switch), the negative from the battery is used to switch this unit on and off unlike normal postive switching, what is the reason for this?



    Any help on explaining the operation of this type of circuit would be greatly appreciated as I have had trouble locating information specifically for this.

    Thanks
    NM
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    The grey part looks to be a transformer. Probably to provide the high voltage for the fence wire.
     
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    It looks like a transformer. Try to measure it's terminals, between several of them there should be a low resistance, if I'm right.
     
    Last edited by a moderator: Aug 2, 2011
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
  5. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    Well, all I can offer is my agreement with the first three members. A step-up transformer is
    most probably.
     
  6. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    And likely an autotransformer. How many of the 6 terminals are actually soldered to a foil trace?
     
  7. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Hi,
    Thanks for re-opening and also the responses and links.

    Yes all terminals are being used, but I am unable to distinguise a primary or secondary, its all open circuit across a combination of terminals.

    I have looked at the circuit some more. From what I can see the osscillator circuit through an external transistor sends 9v to the primary of this component(transformer). From here the secondary of this transformer charges two large capacitors to 250V. This 250V is then sent to the primary of the larger transformer (E3088-11).

    Does this sound right?

    Also the copper inductor, does it act as a current limiting choke? Appears to be connected to the emitter of the transistor and an input on the larger transformer.

    Thanks Again.
    Regards NM
     
  8. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Most electric fences ive worked on have the small grey T/F generates about 200V this charges the 2 blue capacitors. The transistor looking object to the right is usualy a SCR, this is trigered to dump the stored 200V dc across windings of the bigger T/F. This larger T/F feeds the fence. (simmilar principal to a CDI ign).
     
  9. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    With regard to the small transformer is its primary fed from the osscilator, giving a pulsed 200V to the capacitors?


    Do the capacitors then act as a buffer for the pulses before being sent to the larger transformer?


    Or is the oscillator doing two jobs, that is controlling the pulse to the first transformer and also controlling the SCR.

    Thanks for the help.
    NM
     
  10. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Electric fence units dont need very big power supplys as there is plenty of time for the voltage to build up on the blue dump capacitors. The powersupply is probably the small transformer & transistor along side it & is running all the time & self oscillating. The Ne555 timer will be setup to pulse the SCR which will dump the capacitors stored voltage across the primary of the larger T/F, giving quite a hefty voltage on the secondary windings which one side will go to an earth stake & the other will go to the fence.
     
  11. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Some pics of a 9V powered Electric fence & showing 250V DC aprox on the dump capacitor.
     
  12. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Last pic that didn fit . Ones ive had to repair are generaly failed dump cap or SCR.
     
  13. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    debe
    Thanks for the helpful description of operation and for posting the photos. Your version is alot clearer to understand.

    You stated that
    Does this self osscillation work similiar to that of a car indicator/turn signal circuit, using the resistance of the coil to set the switching oscillation?

    One more question with regard to the output.
    This energiser was made redundant and replaced with a larger unit when the fence it was running had to be extended by a couple of fields. This unit has been around for many years and I have failed to locate any instruction manual for it at work or on internet as there is no model or serial number on it.
    Although it is still capable of running smaller fences, I am wondering is it possible to work out its energy rating/output from the board that I have here, so as I can label it and set it aside for a certain size of field.

    Thanks for the help
    Much Appreciated
    Regards NM
     
  14. debe

    Well-Known Member

    Sep 21, 2010
    946
    184
    Hi NM, usually to save costs & parts the powersupply T/F has a primary & secondary & a feedback winding to make it self oscillating. Dont know how you work out is power output. I have never seen any owners manuals. It usualy only involves a decent earth stake for the ground conection & the other goes to the fence. The fence wire does not want any green vegitation leaning on the wire as it will reduce its efectivenes or short it out. The one in my pics is fairly small & used on a small field.
     
  15. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Daryl

    Yeah, I do recell, a while back a company made an enegiser that as a well as giving the HV pulse also at certain intervals gave pulses at a higher current so to create a slight arc which helped to burn off vegitation around the fence.
    Sounded like a good idea but, I think they soon after discovered that in dryer climates it started fires.

    Cant beat the WeedWacker/WeedEater or Strimmer!

    Regards NM
     
Loading...