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Thread: Timer for Bear Fence?

  1. #1
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    Default Timer for Bear Fence?

    My cabin is 110-miles from the nearest human and about 30-miles south of the arctic circle near longitude 114 west in Canada.

    I have a bear fence with a car battery and a 15-watt solar panel. That's enough to keep the fencer working, except during the shortest days of the year (say, December and January) when the fencer probably draws more juice than the panel can replace.

    We can't safely access the cabin (fly-in only) after mid-September, since float season comes to an end at that time and the ice is not safe for a ski-plane until December. Unfortunately, it's just too risky (cold and dark) to fly down there in December to turn off the system.

    I'd sure like to have a timer that would automatically shut down the fence from December 1 to April 1. In this neck of the woods the bears will be snoring at that time.

    Has anyone heard of such a device? My electric fence supplier says they don't exist.

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    If you find a timer that will do what you want, how are you going to power the timer? It will draw more power than the fence.

    What about a switch when triggered will turn on a timer that will keep the fence live for say 30 min then turn off. That way you will not drain the battery. Another idea is to add enough batteries to last five months.

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    Not overly difficult to build a timer based on a 555 timer chip.
    Would take some time and thinking but I could probably come up with something.
    Wouldn't be until later in the year though. I'm busy building my cabin in the woods right now.

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    Until I get the timer issue sorted, I've ordered a big AGM battery. Eventually, I'll replace the 15-watt solar panel with something bigger.

    I was just looking for a less costly solution in the short term.

    Drifter : Keep in touch re: the timer!

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    Plenty of googaws on ebay for temp controlled switch. This one is dirt cheap and may actually operate at the stated temperature. Set it to -10 C or some such and it will probably work for what you need.

    http://www.ebay.com/itm/50-110-DC-12...25.m3641.l6368

    If link doesn't work do a search on thermostat 12v.

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    Quote Originally Posted by ChugiakTinkerer View Post
    Plenty of googaws on ebay for temp controlled switch. This one is dirt cheap and may actually operate at the stated temperature. Set it to -10 C or some such and it will probably work for what you need.

    http://www.ebay.com/itm/50-110-DC-12...25.m3641.l6368

    If link doesn't work do a search on thermostat 12v.
    This is probably the best type of solution to your timer issue. Use the temp as a clock for the winter. I would find a non powered mechanical thermostat set it to open up at -20/-25 c. It would then be shut off at the coldest part of the year which with some fine tuning you should be able to shut down the fence when the bears are hibernating.

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    Quote Originally Posted by retiredinhomer View Post
    I would find a non powered mechanical thermostat set it to open up at -20/-25 c. It would then be shut off at the coldest part of the year which with some fine tuning you should be able to shut down the fence when the bears are hibernating.
    That brilliant!!!!!!! Top job!!!!

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    Yes, that is a very good idea. I'll try it!

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    Been pondering some more on this, and I think rather than futz with a mechanical solution a low-power electronic timer will work well. The digital thermostat I linked above says it draws up to 65 milliamps (mA). Run that for 24 hours and you're looking at 1.56 amp-hours. A 15 watt solar panel in the dead of winter probably cannot reliably keep up with that much energy draw.

    There is an open source platform called Arduino that allows all sorts of tinkering and customization. I googled for low power Arduino solutions and came up with this: https://www.openhomeautomation.net/arduino-battery/

    Rather than power an LED the Arduino can be used to power a relay, which would allow 12V from the battery to power up the fence energizer. The program for the Arduino would need to be programmed to power the relay for 60 days (or whatever is needed) then sleep for 120 days, then power the relay for 200 days. Something like that should work great provided it really is low power and that it will operate at winter temperatures.

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    Thanks for that Chugiak.

    One problem with the thermostat idea is actually finding one that will open the circuit to the fence charger at -25. Such low temperature thermostats are hard to find - if they are available at all.

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    Yeah, that was my thought too. Something specific to your needs might be out there, or you might have to get a standard mercury switch thermostat and modify it. I would thinnk that calibrating something like that would be a challenge.

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    You are going to have to spend some big money if you expect electronic and batteries to work at temperature below -25*f for very long. What did people do before there was electrical fence?

    A wind generator or a thermoelectric generator is another option to power the electronic when there is no sun.

    You could dig a hold 10-15 feet down and put the batteries and electronic in. The earth heat will keep the equipment warm.

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    A quality lithium AA battery will be fine down to -40 as long as you aren't drawing too much current.

    http://data.energizer.com/PDFs/l91.pdf

    My brain is still gnawing on this puzzle. Gonna root around in Mr. Google's cellar and see if there's info on how to have a reliable low power, low temp timer.

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    Relevant to any sort of control circuit, mechanical or electronic: what is the power draw of the fence charger?

    Edit: current actually, is what I would like to know.

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    Remember that moncrystalline solar panels are more efficient in cold weather and the sun bouncing off the snow helps too.
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

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    I saw this document on this type of thermostat You will need the type that has the no/nc/com terminals and you want to connect to the nc terminal so when it gets cold enough the contact opens up turning off your fencer.
    http://www.thermon.com/catalog/us_pdf_files/tmp0022.pdf

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    US $170 will get you a simple. adjustable, thermostat.

    http://www.omega.com/pptst/TSW.html

    I think the TSW-11 or the TSW-21 will work nicely. If I were to buy one I'd opt for the TSW-21 as it has a more useful range of temps.

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    Quote Originally Posted by MacGyver View Post
    You are going to have to spend some big money if you expect electronic and batteries to work at temperature below -25*f for very long. What did people do before there was electrical fence?

    A wind generator or a thermoelectric generator is another option to power the electronic when there is no sun.

    You could dig a hold 10-15 feet down and put the batteries and electronic in. The earth heat will keep the equipment warm.
    My game camera worked through last winter and I got a year and a half out of a set of lithium AA cells.

    There's very little wind at our cabin, judging by the un-drifted snow photographed by the game camera.

    It might be a little warmer in a hole in the ground, but we're in permafrost here so that's probably not an option.

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    Quote Originally Posted by ChugiakTinkerer View Post
    Relevant to any sort of control circuit, mechanical or electronic: what is the power draw of the fence charger?

    Edit: current actually, is what I would like to know.
    Sorry - that I don't know. And the spec sheet for the fence charger (Parmak Mag 12) doesn't provide that little detail.

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    I still think an Arduino configured to run on very low power coupled with a latching relay would be cheap and functional. Just something that would involve some bench configuration and programming. Coupled with a real-time clock chip or a GPS module, you could set it to the gnat's ass as far as when to turn off the fence and when to turn it back on.

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