I am looking to build an electric rat trap that acts like an electric fence, one that that can deter or block rats from climbing up a tree. Not interested in killing them.

I have a large orange tree that we love, unfortunately so do all the neighborhood rats. Every night they run up into the tree, eat into several oranges, leaving debris all over the ground. In a couple months time, all our oranges could be gone.

I don't want to poison them (we have dogs), snap traps are mostly useless, and if they work, it gets just one. There are always a bunch more in the area that follow.

I'd like to build an electric "fence" that can shock them as they climb up the tree. I saw on youtube how they do this:

Take a 12V battery, connect it to a 150 uF AC Capacitor, which then connects to two sheets of aluminum/steel (positive to one piece, negative to the other). Each piece of aluminum/steel will wrap around the base of the tree, spaced an inch or two apart, so when they climb up, they get shocked, and fall off.

This is one example of a setup that I found:

enter image description here

The negative line of the batter goes straight to one piece of metal/aluminum, the positive goes into one capacitor, then into another, and then to the other piece of metal/aluminum.

As I got this off of YouTube, I was hoping for clarification on a couple things.

  1. Would this setup work? If not, what changes would be needed?
  2. How to make it safe? I would disconnect battery at night and reconnect in morning. I don't want my tree to catch fire, and I don't want to electrocute myself.
  3. What kind of shock would I expect if I personally triggered it - touched both pieces of wire.
  4. How long would battery last, if nothing touched it? I assume I would have to recharge the battery at some point?
  • \$\begingroup\$ If I was a starving rat, would I risk a shock for an orange? I probably would. I might even risk it even if I was not starving because oranges seem pretty rare compared to other foods. Also, I heard rats cooperate. So maybe one rat could get up there and knock oranges down. Assuming the rats are getting into the tree only from the ground, you can't just wrap the trunk high-up in barbed or razor wire? \$\endgroup\$ – DKNguyen Aug 1 '19 at 19:43
  • \$\begingroup\$ Rats will figure out how to jump from + grid to - grid in the air and try galvanized steel mesh arbor-shield.com/wire-tying-tool \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 1 '19 at 19:47
  • \$\begingroup\$ You could use the high voltage generator intended for a regular electric fence. These generate regular pulses of a few kilovolts, so only need one conductor 'web' around the trunk, the shock is largely a result of the capacitance of the body rather than relying on grounding. It'd give you a fairly unpleasant but far from lethal shock, but a rat getting zapped on the snout would be fairly memorable for them. \$\endgroup\$ – Phil G Aug 1 '19 at 20:05
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    \$\begingroup\$ It must be rain and rust proof. so as not to shock the tree. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Aug 1 '19 at 20:06
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    \$\begingroup\$ Hi Greg, I'd say to go for a simpler approach. Cut a big cone out of some thin aluminum sheet (not foil), with a hole slightly larger than the trunk in the center. Mount this to the trunk in a way that will not damage the tree and can easily be adjusted and moved. Then nothing will be able to climb the trunk, day or night, and it needs no batteries. \$\endgroup\$ – rdtsc Aug 1 '19 at 20:58

Would this setup work?

No. This circuit is complete nonsense -- the voltage from a 12V battery is too low to produce a shock, and connecting capacitors in series with the battery will prevent any current from flowing at all. Unfortunately, I suspect that the tutorial video you watched was fake. (Sadly, this is rather common.)

Creating a circuit that would be effective in this scenario would involve completely different parts -- one option would be to use a transistor oscillator, a high frequency step-up transformer, and a voltage multiplier, similar to the circuit used in an electric flyswatter. However, this would require a lot more parts and some careful design -- there is no way of turning the parts you currently have into something functional.

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Why bother? Wrap the trunk of the tree with a smooth, slippery surface, like polyethylene sheet, or aluminum. The rats can’t climb that. That’s what they use for date palms.

Relevant: https://homeguides.sfgate.com/keep-rats-out-citrus-trees-35657.html

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  • \$\begingroup\$ Really? That works? I would have though the polyethylene sheet or copper could be dug into or or dented something with claws, but I am not a tree climbing rodent. \$\endgroup\$ – DKNguyen Aug 1 '19 at 22:19
  • \$\begingroup\$ How thick of a copper sheet do you actually need? Does it have to be thick enough to "hold it's form"? Or can it be thin enough that you can fold it rather than bend it? \$\endgroup\$ – DKNguyen Aug 1 '19 at 22:31
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    \$\begingroup\$ No, it's that the copper is distasteful to slugs and snails (it's toxic to them) so they will not climb it. \$\endgroup\$ – hacktastical Aug 1 '19 at 22:49
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    \$\begingroup\$ @DKNguyen: "What's the difference?" Cost and availability. I wrapped copper wire around the stems of our indoor tomato plants. No more slug trouble. I like to imagine them getting an unpleasant tingly sensation on their slimy stomachs as they try to go across it. \$\endgroup\$ – Transistor Aug 1 '19 at 22:53
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    \$\begingroup\$ @Transistor I really hate it when those indoor slugs attack my indoor tomato plants. ;) \$\endgroup\$ – jonk Aug 2 '19 at 2:29

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