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Electric Fence Charger

Discussion in 'Power Electronics' started by Richard C, May 23, 2018.

  1. Richard C

    Richard C

    4
    1
    May 23, 2018
    Greetings ~ I'm working on a fence charger .. The 110 volt enters the power supply board ~ I smell what I think is the smaller capacitor on the board ~ I traced continuity that far ```

    Question : can I test continuity of the capacitor ? while it's still on the board ?

    When I try to test continuity on the board across the capacitor ~ I get nothing ```

    What think you ?

    Thanks

    Richard
     
  2. Alec_t

    Alec_t

    2,514
    652
    Jul 7, 2015
    The continuity test function on a multi-meter performs a DC test. Capacitors are designed to block DC, so will appear to be open circuit.
     
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  3. kellys_eye

    kellys_eye

    4,286
    1,143
    Jun 25, 2010
    Make, model, schematic, pictures?
     
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  4. Richard C

    Richard C

    4
    1
    May 23, 2018
    Parmark Mark 8 sorry no schematic I do get a reading with the tester on 200 ohms ~ so there is continuity just now ~ the capacitor is 470 uF 35volt ``` the board smells like that's why I'm thinking the cap is cooked ``` IMG_0879.JPG IMG_0878.JPG
     
  5. Alec_t

    Alec_t

    2,514
    652
    Jul 7, 2015
    Unless you unsolder and lift one leg of the cap, your measurement will be affected by any impedance in parallel with the cap.
    If you measure the isolated cap using an Ohms setting, you would expect a very brief low Ohms reading while the meter charges the cap. The resistance reading should then increase to a very high value if the cap is not leaky.
     
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  6. kellys_eye

    kellys_eye

    4,286
    1,143
    Jun 25, 2010
    What voltage do you measure across that capacitor when the unit is powered?

    The most common problem with fence energisers is the main discharge capacitor - looks like the big blue rectangle on your board (??? 5.6μF ???)

    This is the most stressed item in the unit and the symptoms include a low energy spark (or none at all).

    You should (might.... depends on your age!) be able to hear the squeal as the inverter circuit charges the capacitor - this will indicate that the circuit is basically working. If you CAN hear the squeal but the unit still isn't sparking, change the big capacitor.
     
    Richard C likes this.
  7. Richard C

    Richard C

    4
    1
    May 23, 2018
    Hi ~ the main capacitor is a large silver one lying down on top of each picture ``` Power , I believe , is not coming from the power supply ~the is no LED read out ~ and yes the main CAP had no charge ``` I didn't get a reading across the Capacitor ~ I did get quick read out ~ as Alic mentioned ~ but I didn't register a reading ~ no ~I wouldn't hear a squeal ```
     
  8. 73's de Edd

    73's de Edd

    2,483
    1,010
    Aug 21, 2015
    Sir Richard C . . . .

    Top picture . . .

    Pity that this is just being a micro-tad . . . . out of the 1 year parts warranty ?

    I would see the large silver canned capacitor as being the " BIG BANG " poly capacitor which repetitively charges up, to then get discharged into the primary of the HV spark transformer which . . . . you can just see its right half of, to the left..
    Assuredly the 470 ufd main low voltage power supply capacitor is being the brown unit, mounted just off center in the main PCB.

    I feel that one side of the HOT raw AC line power is coming in thru the white ceramic block power resistor, after it passses thru adjunct varistors and current inrush thermistors, and routes thru the BLUE block 5.6 ufd capacitor, to then end up at the set of 4 side by side FWB rectifiers seen as D1-2-3-4 and then they feed over to that 470 to initially provide your LV DC power.

    TESTING . . .

    In a no power applied condition . . . . . take ohmmeter leads and see how your DVM meter reads in a shorted together probe test .
    Then take the leads and test from the cathode bands of those 4 diodes to see if 2 of them follow a path to directly connect to the + of that 470 electrolytic.
    Same way with the opposite leads ( anodes . . .no silver bands) . . . of the diode sets, to see if 2 of them end up connected to the - of the electrolytic.
    If so, that is your circuitry source for the LV supply.
    In a powering up . . . .
    If no LV power, then just track the HOT AC line thru the components that I mentioned to a combined anode cathode connection into those diodes .

    Does this particular "8" unit use a central analog meter on the front of the panel, or a digital LED 7 segment display?

    Other diodes on the board seem to be a small signal 1N4148 for D5 . . . . .while the larger D6 beside it and the somewhat separated D7-8 sets might be Zeners, so one of them being dead shorted, might account for the loss of that power supply.

    73's de Edd
    .....
     
    Last edited: May 24, 2018
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