Powerful Solenoid Design

[dellsam34]

Dear engineers,
I want to build a powerful solenoid yet very fast and of a stroke of 50-80mm, Kind of like this one but with more torque and speed with a return spring, Since I need a trigger and another 4 seconds to prevent a re-trigger I was thinking of using a super capacitor, When a trigger happens the super cap delivers a jolt to the solenoid giving a powerful and fast blow and recharges again and wait for the next trigger, This is a project for a rodent trap, the solenoid's core or rod will deliver a powerful punch and retracts when the charge is depleted, the recharge begins, the rodent drops and trigger is set again for the next catch.
I just don't know where to start, what kind of wire gauge, number of coils, what high voltage, what super cap and what circuit to charge it with?

[CaptDon]

Super Caps aren't designed for fast charge or heavy discharge. They are more like a really poor excuse for a battery to hold up volatile memory or supply power during momentary power interruptions. Most Super Caps want to see a charge cycle of not less than 20 to 30 seconds. For power you would want at least a gelcell. Even the 12v 12ah batteries can briefly push 30 to 40 amps and still maintain 10 volts. Seems like a lot of trouble to kill rodents. Aren't there already 100 solutions on the store shelves?

[Circlotron]

I'd try a conventional electrolytic cap that discharges into the solenoid via an SCR, with a reverse diode in parallel with the solenoid so the inductance doesn't charge up the cap in the reverse direction. Circuitry and operation is similar to an automotive capacitor discharge ignition. Seeing the current only flows for a moment, you could give the solenoid quite a pulse without overheating.

[themadhippy]

The capacitor discharge units used by railway modelers to fire point motors might be worth a look

[ajb]

What's that saying about a better mousetrap? 

This is kind of a mechanical engineering question first and foremost, the electrical engineering would come after you determine the mechanical requirements of the solenoid.  I would actually question whether a solenoid is what you want at all here.  A solenoid like the one in the linked video operates at hundreds of watts.  Increasing the speed requires increasing the force to accelerate the moving part, and increasing force requires increasing power.  Using a motor to wind up a spring that provides the required force when released might be a better fit -- there are very large automatic circuit breakers that use this method, for example. 

[dellsam34]

Oddly enough a motor with a strong spring that gets coiled and released via a small solenoid was my initial idea, I backed out of it because it's a complicated design, I though a powerful solenoid is much easier to design mechanically and electronically.

[dellsam34]

The capacitor discharge units used by railway modelers to fire point motors might be worth a look

Any links to such a product?

[dellsam34]

Seems like a lot of trouble to kill rodents. Aren't there already 100 solutions on the store shelves?

That's not really the point here, it's just a fun project, 80% of rodent traps on the market don't actually work the way they are marketed anyway, if they work at all, the animals get smarter every time they are exposed to them, I have some that are set for months and not a single catch and they are put the same way videos suggested they actually work, My goal is to make the design as hidden from the rodent pathway as possible so they wouldn't get suspicious or learn the design, it's more fun than actually getting the job done.

[ArdWar]

What ballpark of force, stroke, and probably duty cycle are we talking about here?

Fast and powerful actuation while parts still COTS sounds like a job for electropneumatic.

[themadhippy]

Any links to such a product?

https://gprivate.com/6bhbk

[soldar]

I recently repaired an old light timer where you would push a button and the lights would stay on for s programmable period of time. It has a solenoid and a clockwork mechanism. I am not surprised the thing broke itself apart because the jolt of the solenoid is very violent.

If I were to use it to open a latch, as I was thinking, I would put a spring in between because such violence will break anything connected to it that is not very strong.

[thm_w]

Super Caps aren't designed for fast charge or heavy discharge. They are more like a really poor excuse for a battery to hold up volatile memory or supply power during momentary power interruptions. Most Super Caps want to see a charge cycle of not less than 20 to 30 seconds. For power you would want at least a gelcell. Even the 12v 12ah batteries can briefly push 30 to 40 amps and still maintain 10 volts. Seems like a lot of trouble to kill rodents. Aren't there already 100 solutions on the store shelves?

They are fine for fast discharge, you just have to buy the right one. They are commonly used in spot welders.
Here is one with 0.2R ESR: https://www.digikey.ca/en/products/detail/kyocera-avx/SCCZ1EB308SWB/12663727

[CaptDon]

Those 2.7 volt caps may work great for spot welding where the weld resistance is in milliohms, but to slam a solenoid is going to take a bunch of those caps in series/parallel to get a bang out of a solenoid that will be at least an ohm or two and need a 50 amp pulse as a rough guess. I think I would set up some kind of heavy tray suspended about 2 or 3 inches above the floor with a release latch mechanism to smash the little rodents. Personally, I like the old farmers trap where they simply fall into a bucket and drown. I used to find them that accidentally fell into my horses 5 gallon water buckets sitting on the floor of the stalls. The horses weren't very happy!!

[dellsam34]

What ballpark of force, stroke, and probably duty cycle are we talking about here?

Fast and powerful actuation while parts still COTS sounds like a job for electropneumatic.

Not sure about the exact unit of force but anything that punches a rat will be good enough, Stroke is around 70mm (3"), The duty cycle is as follows after the trigger and punch anywhere from 4 seconds to the next trigger, I had designed one with a pneumatic tank and an air cylinder but it runs out of air pretty quickly, I used a small scuba tank (probably 10L) at 170 PSI but didn't last long, So I scrapped that.

[dellsam34]

Any links to such a product?

https://gprivate.com/6bhbk

I had googled it and it came with a lot of stuff that I'm not sure what to make of, hence asking for a specific solenoid link, By the way your "let me google that for ya" link does not work.

[NiHaoMike]

Isn't the most obvious way to build a pest trap with a capacitor is to use one that is high voltage and lure the pest into a gap connected to the terminals? Takes care of the detection and the execution part in a very simple manner.

[soldar]

Designing and making a solenoid requires more study and work than you could ever do and it makes no sense when you can already buy all sorts of solenoids commercially.

If you want to play around you can make a solenoid with some old transformer you do not need. Just drill a hole down the center

You can even make a cannon. Look at this video in Spanish at time 8:20:

https://youtu.be/zWdyD-0qQgQ?t=510

[salihkanber]

I also want to approach this issue from a different angle. To obtain a strong solenoid, it is necessary to create a high magnetic flux. One way to achieve this is by applying high electrical power, which is correct, but for this power to generate a high level of magnetic flux, the material used inside the solenoid must also have high magnetic permeability. Solenoid manufacturers use alloys that provide higher magnetic permeability compared to normal iron or steel. For this, you can check 430FR steel material.

[max_torque]

come on peeps, it's 2024, can we please try and use a bit of physcis and science before we all just make stuff up 

1) how much energy is required to kill (or stun) a rodent - benchmark / measure an existing solution
2) How quickly does an existing solution release that energy (ie the power rating)
3) How quickly does the trap need to reset (unless it's a rodent appocolypse then surely pretty slowly, ie if it takes 10min to rest is that an issue
4) What are the size limits and portability limits for this device
5) does it need to be standalone, ie containt it's own energy
6) how long does it need to be set for and remain viable

Answer those, and the best mechanical and electrical solution will present itself. Just randomly trying stuff is going to make for a long winded project with very poor results....

[MarkT]

Solenoids are very inefficient as the magnetic circuit has to start open and becomes closed during the stroke, limiting the efficiency.  Why not use a motor and rotary action?  Also a right-angle beam on a motor shaft can go a lot faster than the internals of the motor - just ensure its balanced for best action.

[soldar]

A solenoid can work fine for this application and, believe me, an adequate solenoid can very easily exceed the requirements. I have a solenoid here that will crush a finger if it catches one.

You can buy a commercial solenoid ready made and it will work fine.

[dellsam34]

A solenoid can work fine for this application and, believe me, an adequate solenoid can very easily exceed the requirements. I have a solenoid here that will crush a finger if it catches one.

You can buy a commercial solenoid ready made and it will work fine.

Any model or link to your solenoid?

[dellsam34]

come on peeps, it's 2024, can we please try and use a bit of physcis and science before we all just make stuff up 
Answer those, and the best mechanical and electrical solution will present itself. Just randomly trying stuff is going to make for a long winded project with very poor results....

Most of those question have been answered already:
1) how much energy is required to kill (or stun) a rodent - benchmark / measure an existing solution > Enough to crash a soda can per say.
2) How quickly does an existing solution release that energy (ie the power rating) > in milliseconds, rodents, especially mice are pretty darn fast.
3) How quickly does the trap need to reset (unless it's a rodent appocolypse then surely pretty slowly, ie if it takes 10min to rest is that an issue > few seconds up to few minutes is fine.
4) What are the size limits and portability limits for this device > No size limit, Li-Ion powered, no compressed air or electricity is available.
5) does it need to be standalone, ie containt it's own energy > Yes
6) how long does it need to be set for and remain viable > Few days, preferably few weeks, but if it runs out of power it is not a big deal, I will use replaceable battery packs.

[Jeff eelcr]

Back in the early 80's I worked for a company that made a camera timer solenoid unit they wanted redesigned (cheeper).
We bought about 50 different solenoids from various manufactures and tried them all although some did work, none was
as good as the one we were using but all were cheeper.

[Marco]

This is less a solenoid and more a captured bolt coilgun.

What's the advantage over electrocution?