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Design for a mains-powered rat zapper circuit

Thread starter #1
Our property has a rat problem. My goal is to build a powerful electric zapper that kills them by electrocution. The electrocution mechanism will be bolted to the top of a 55 gallon drum that's half-filled with water. After the rats are zapped they will drop into the water, and if any survive the initial deadly shock they will drown. A trap like this could kill hundreds of rodents before needing to be emptied, and this is one of my goals -- a trap that will work repetitively for weeks or months with zero attention.

I would like to use 110vac as my power source, not only for reliability but also to eliminate the issues of battery charging and/or replacement. However, since DC is reportedly more effective than AC in this application, I'm thinking that I should rectify the AC voltage to DC.

I would like the final circuit to work consistently for years or decades, and I want it to kill instantly 99-100% of the time. To me this suggests boosting the voltage so there will be no question that every rodent that completes the circuit will die immediately. I understand that a circuit like this could kill a human, so I will put it inside a housing that requires unscrewing and disassembly -- just like old analog TV's, microwave ovens, etc. which always have their dangerous parts safely enclosed and protected from curious fingers.

I'm not an electronic circuit designer, but I know how to work safely around high voltage sources. I've worked as a residential electrician for years, and many years earlier my Dad (a TV repairman in the 50's and 60's) taught me how to safely extract vacuum tubes, capacitors, coils, transformers, and other electronic goodies from the old CRT TV sets he invariably ended up with through his work.

I'm looking for "industrial" quality here, meaning relative simplicity combined with power and exceptional reliability. Could an effective (yet minimal) circuit for this project be as simple as feeding the 110vac line voltage into a step-up transformer, then to a bridge rectifier, then to a large capacitor, then to the contacts where the rat will complete the circuit?

I'm seeking confirmation (and if possible a schematic) for a simple circuit that would work consistently and reliably, and also discussion / suggestions about such a project so I can learn from those who know more about high voltage circuit design than I do.
 

dknguyen

Well-Known Member
Most Helpful Member
#3
Why would you need it to be a deadly zap if it's already above a tank of water? Just enough of a zap to make them lose control and fall in and drown would be enough.

You don't even need a zap. Just a teetering or spinning bridge or plank that drop the rat into the water when it walks. Lots of traps like that on Youtube that are super super effective. Safer, more reliable, runs forever, and can be put anywhere with no need of consideration for mains wiring.

Apparently, one of the most effective is a spring-resetting, magnetically latched hinging plank. A cantilever with a hinging joint is used with a weak resetting spring (the weaker the better so the lighter the cantilever the better). The cantilever is also prevented from hinging action with a magnet that is tuned to suddenly release when the torque due to the mouse's weight when it goes too far down the plank. The magnet lets the mouse get farther out to the end of the plank so it can't jump back in time. Two planks on opposite sides that meet at the middle end-to-end make a deceptive bridge, should you so desire.

I am curious how you plan to get a trap to work for months with zero attention with regards to bait though. Unless by zero attention you just mean without emptying the trap, rather than not needing to bait it for months at a time.
 
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Thread starter #4
Thanks for the link Mike, I will look into it.

Mice are curious by nature so "walk the plank" and "rolling log" methods work well with mice ... but I'm not after mice. Rats on the other hand are cautious by nature, especially the older and wiser ones. We have tried many non-electric methods including "walk the plank" and "rolling log" and several variations ... and many other methods. While we catch one now and then with some methods, the growth of our rat population far exceeds the occasional kill we see with all other methods.

I have monitored our rats at several traps by remote video. They won't walk on or step on anything unless it is stable and solid. If they walk on a steel pipe that's solidly installed in my proposed trap, they won't be scared and they won't shy away from it. This gives us the best chance of shocking the rat through his entire body from his nose/mouth to his feet ...

I'll put several cups of seeds, dog food, etc. into the trap for bait. The rats will smell it, but they won't be able to get to it until after they complete the circuit by touching the wire basket that holds the bait. Therefore the bait should not need replenishing very often. However ...

You are correct that I should not have said "zero attention" for weeks or months. What I actually meant is that I want to collect dead rats in a large barrel for weeks or months before having to empty it, but I will monitor the trap via remote video daily to confirm that it is working. I will also visit the trap physically at least weekly to refresh / replenish the bait as necessary.

And you're right, I only need to shock them long enough to cause them to lose their balance and fall into the water. However, if the shock kills them instantly, they won't be able to swim around for hours, squealing in fright or calling to other rats to warn them of the danger. And if they die instantly their bodies will not release any natural chemicals / pheromones / odors that might warn other rats of the danger. But even if such odors were released after their death, those odors will be mostly or completely trapped under the surface of the water as they sink to the bottom of the barrel.
 

sagor1

Active Member
#5
"those odors will be mostly or completely trapped under the surface of the water as they sink to the bottom of the barrel. ".
My understanding is that bodies will float after several days due to bloating (decomposition). So that theory may or may not be true, as I don't know if rats have different decomposition byproducts. Something to think about.
Another thing, rats, and many other animals, may be able to sense the small corona discharge around an electirfied device. If rats are as cautous as you say, they may sense something "wrong" with that metal pipe. Have you tried anything to test this theory yet? Worth trying something simple next to a "plank" method to see if the rats react to an electrified device. If the rats react to a steady charge, you may have to devise some trigger device to turn on the DC, like an optical sensor or something.

Good luck...
 
Thread starter #6
I have not tested my concept yet (I'm not a circuit designer so I would need a basic circuit drawing to follow as I build a test circuit) ... but if the rats sense the electrical charge field I will probably go back to my original concept:

Use a microswitch to turn on the power to a cheap Chinese high voltage power generator:

These high voltage generators are reported to burn out if the power is left on for any length of time. I think they are used in stun guns so they can handle very short power-on times, but they would burn out after several minutes if powered continuously. I thought about going this route in the beginning, because turning on the battery power to the hv generator -- only when a switch is closed -- would dramatically extend the life of the battery vs. triggering the circuit with a PIR sensor. This would also give me the ability to place the unit anywhere I desire.

However, creating the mechanical system that insures the rat's body is in a position to conduct electricity at the same time he triggers the switch is not as easy as it sounds, especially when compared with a capacitor-discharge zap that occurs automatically when the rat is standing on a steel pipe and gets his nose close enough to the wire bait basket to complete the circuit.

Basically I think the capacitor-discharge method of letting the rats complete the circuit with their bodies would be more reliable than using a microswitch or a PIR sensor, assuming the rats are not bothered by the corona discharge you mentioned.

I watched a video of a rat getting zapped by 220vac mains when he licked the peanut butter on the plus terminal while he stood on the minus terminal. He got shocked, but he came right back and did it again -- twice. It is evidence like this that makes me hope that maybe the rat won't be bothered by corona discharge. I may not know if this will be an issue until I actually build something and test it.
 

unclejed613

Well-Known Member
Most Helpful Member
#7
what size are the rats? it might be better to get some cats. you won't have to worry about the danger of fire or high voltage. rats will avoid territory marked by cats too. i used to live out in the country, and had an average of about 10 barn cats at any given time. never had any problems with mice or rats.
 
Thread starter #8
We cannot have cats because (1) our son is allergic to them, and (2) they hunt and kill our poultry, especially the young ones. In fact we constantly trap stray and feral cats, opossums and raccoons in order to protect our poultry.

Thanks for all the alternate suggestions, but I really hope to have the electrocution trap I conceived of long before I came to this forum.

How about if I just hook up this transformer and be done with it? This would probably be much simpler (and maybe even cheaper) than soldering together a circuit from scratch ... and if I'm not mistaken, a jolt from this transformer would likely knock the largest rat off his feet:

https://www.ebay.com/itm/Neon-Light...pply-HB-C02TE-3KV-30mA-5-25W-Kit/352515876329
 

dknguyen

Well-Known Member
Most Helpful Member
#9
We cannot have cats because (1) our son is allergic to them, and (2) they hunt and kill our poultry, especially the young ones. In fact we constantly trap stray and feral cats, opossums and raccoons in order to protect our poultry.

Thanks for all the alternate suggestions, but I really hope to have the electrocution trap I conceived of long before I came to this forum.

How about if I just hook up this transformer and be done with it? This would probably be much simpler (and maybe even cheaper) than soldering together a circuit from scratch ... and if I'm not mistaken, a jolt from this transformer would likely knock the largest rat off his feet:

https://www.ebay.com/itm/Neon-Light...pply-HB-C02TE-3KV-30mA-5-25W-Kit/352515876329
Yeah. probably not worth the effort to change to DC. You get different reports about AC or DC being more hazardous than the other anyways. For DC you'd probably just used a bridge rectifier to make it go from -Vp to +Vp so that it only goes from 0 to +Vp and then a capacitor to smooth it out into DC (more or less with some ripple). But that capacitor prevents a danger in that it holds a charge after power has been disconnected. Plus depending on the cap, it might not fare well in the elements.
 
Thread starter #10
For DC you'd probably just used a bridge rectifier to make it go from -Vp to +Vp so that it only goes from 0 to +Vp and then a capacitor to smooth it out into DC (more or less with some ripple).
This is the basic concept I had for a simple rat zapper circuit when I first started this thread. But I'm not a circuit designer, so I would have been guessing at the correct specs for the bridge rectifier and capacitor if left to design the circuit on my own.

But that capacitor prevents a danger in that it holds a charge after power has been disconnected.
I was thinking about using a bleed resistor across the capacitor terminals to quickly discharge it to a safe level when powered off. Since I would (theoretically) be the only one who ever gets near this circuit, a bleed resistor would not be necessary for my personal safety, but I think it would provide an extra level of safety for others who might assume that it is safe to touch after being unplugged.

Probably not worth the effort to change to DC. You get different reports about AC or DC being more hazardous than the other anyways.
Since there's no clear consensus on which would be more effective in this particular application, I agree that it's probably just a waste of time/money to complicate things by converting to DC, especially when a reasonably powerful neon transformer is available on eBay for less than $10 and would (hopefully) kill any rat it zaps.

My only concern with the eBay neon transformer (aside from the fact that it's made in China so the quality might be suspect) is whether or not any damage will occur if it is left on all the time with the secondary circuit open? This won't hurt the transformer, will it?
 
Thread starter #13
It looks like off-topic remarks are being posted now, so I think it's time for me to leave. Thanks for the opportunity to ask questions and learn more about the way to create my rat zapper trap.
 

ChrisP58

Well-Known Member
#15
Ditto to all safety concerns posted.

That said, I'd use an electric eye switch such as this to energize the primary of your transformer. That way the power is not turned on until the rat is in the kill zone, and it turns off as soon as the rat falls away.

But I wouldn't use a neon sign transformer. You don't need that much voltage to kill a rat that's walking around barefoot. I'd just use a 120 to 240 VAC isolation transformer. You just need to make the plank with two contact strips, so that it's left and right feet are on different terminals of the transformer.
 
#19
The idea is to cannibalize the electronics. You don't have to keep in the same case.

Do you have any idea as to what voltage and current are needed to kill a rat?

Apparently they do, since I have a friend who has one and it works quite well. (Over 20 kills.)
 
Thread starter #20
And apparently you don't care about safety.
I think this is an unwarranted comment given the fact that you have no idea how many or what kind of safety features I intend to build into it. Why wouldn't you ask how I intend to make it safe BEFORE making such a comment?

What if I had asked about building a neon sign with the neon transformer I mentioned above? Would you also assume that I would build in such a way that it would be unsafe? Or is your assumption of unsafety based simply on the fact that I have asked about a rat zapper?
 

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