power supply question

Discussion in 'General Electronics Chat' started by Orgone Energy, May 15, 2015.

  1. Orgone Energy

    Thread Starter New Member

    May 12, 2015
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    I need to power a DC / battery electric fence charger to keep my sheep on our farm. I don't have a spare 12v battery to use for it. But i do have the power supply from a cable tv amp rated @ 12vdc 800ma. I have looked up the fence charger on line but the company does not provide info regarding how much power it draws @ 12vdc but i have found other fence chargers that are simular and there power draw is 12vdc @ 50-80 mah.
    Would my cable tv amp 12vdc 800ma power supply work?

    Thank you in advance. .
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    If the manufacturer doesn't publish current draw specifications, the only thing you can do is try it and see.
     
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  3. crutschow

    Expert

    Mar 14, 2008
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    3,244
    It it's normally battery powered then it likely doesn't take more than the 50-80 mA (not mah) that you found for similar fence chargers so the adapter you have should work fine.
     
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  4. ScottWang

    Moderator

    Aug 23, 2012
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    If you treat the charger draws 50-80 mah as you buy something that you have to pay, then the 800ma from power supply as the money what you have in hand, do you know the meaning now?
     
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  5. studiot

    AAC Fanatic!

    Nov 9, 2007
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    The charger will work just fine, as already said.

    However there remian a couple of considerations.

    Firstly the current draw is not published because it depends on the load not the charger.
    That is it depends on the length of electrified wire. You will find that a minimum length is specified by the wire manufacturer and if you use less you run the risk of burning out (or worse) the power supply. Conversely a longer length of wire will draw less current.

    Secondly there is one of safety.
    A purpose designed supply will have some form of protection (fuse?) in case there is a fault where the mains feeds through to the output.
    The CATV supply probably won't have this.

    You should ensure there is a 1amp fuse in the mains supply.

    There's lots of lambs at this time of year.
    Happy rearing.
     
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  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,394
    1,606
    As an aside have you seen devices such as the Fi_Shock produces? They are self contained solar powered electric fence chargers.

    We use one on top of a lighthouse we volunteer to keep in good order. In that very harsh environment (salt water is a killer) it lasts us near 10 years without replacement. There are replacement batteries available for the one we use (if we ever need one).

    I would not offer any guesses about your question without knowing what unit you are connecting to.
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    I doubt that is the case - electric fence units are usually capacitor discharge type.

    An inverter develops something around 200 - 350V, that charges a capacitor which is dumped into a high voltage pulse transformer. The simplest trigger is a neon tube relaxation oscillator that fires an SCR.

    Projects to build these used to appear quite often in various hobby magazines. Most often they were based on a car ignition coil.

    There may be an adjustment for pulse repetition rate, that turns the wick up on the inverter so the C/R in the relaxation oscillator charges more quickly - that's what would increase current draw.
     
  8. Orgone Energy

    Thread Starter New Member

    May 12, 2015
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    Erniem,
    Thanks for the suggestion, our main charger is a solar system but the biggest problem is keeping the battery's charged. I was trying to figure out a way to use a different fence charger that ran off a 12v battery when the sun was not out and also to make sure i had a werking spare incase or solar one breaks. Problem is i don't have a spare battery to run it but i do have boxes of different power supplies collecting dust so i just wanted to make use of what i have inserted of spending more money. Farming is expensive. Even on 4acres.
     
  9. Orgone Energy

    Thread Starter New Member

    May 12, 2015
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    0
    Thanks.;)
     
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