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Electric Fence Zapper

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madlabs:
Hi All,

I'm working on a electric fence zapper to keep critters, including bears, out of my orchard. Since the zappers one can buy seem too wimpy for bears, plus what fun would it be to buy one, I decided to make one myself starting with a ignition coil. Right now I am pulling a bright 1" spark. Haven't had the guts to touch it yet, I'm scared. :)
 
So, I'd like a little help confirming that what I have designed seems reasonable. I am using a 7aH, 12V SLA battery. The coil's primary measures 1.2 ohms. The circuit uses 10mA. I am going to charge it with a 5W solar panel that has almost perfect solar exposure.

1.2 ohms = 10 amps @ 12V = 120 watts.
The circuit activates the coil every 3 seconds. This means 28,800 zaps per day.
The pulse length is 6mS X 28,800 = 172 seconds of on time per day, or .048 hours per day.
120 watts X .048 = 5.76 wH / day
10mA = 2.88 wH/day + 5.76 wH/day = 8.64wH/day total. Assuming 30% charging inefficiency, 11.23 wH/day.
7aH @ 12V = 84wH/day, so in theory 7.4 days of battery life.

Seems to me that should work out fine and have decent battery life. I will be using a simple LM317 adjustable regualtor for a charger. Since I am not using a "real" charger, what voltage should I set it at? 13.8? A little higher?

Thanks!

Jonathan

ghurd:
I would use 13.8V.

If your circuit math is right, the 5W panel should keep up just fine.

Might want an LVD on it in case a shocked bear knocks in down.
G-

Norm:
to test it hook up to a cattle prod and wait for a bear to come 'round?
leap of faith !    LOL !
Norm ;)

madlabs:
Ghurd, by LVD do you mean low voltage dropout? If so, gotta simple circuit? I am just putting together the art for the final PCB to include the charger and so could add some stuff. Although I am tempted toi make a sub board since the zapper PCB turned out so nice.

Norm, you're the one with the lightning bolt on your picture, YOU test this thing! :)

Thanks, Jonathan

bj:
One inch spark?  I'll be standing in the coward's line.

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