How much current to kill an insect?

requires evaporation, not just stopping the heart. I could connect a milliammeter across the USB one's output, but I don't want to break the meter if there's a strong pulse to start with. The USB one states 1A 5V input, so the output couldn't continuously exceed only 3mA, unless it drops to 100V and gives out 50mA, and the output drops from 1700V to 0V immediately I turn it off (with an antique electrostatic voltmeter connected which may draw a bit).

Is your electrostatic voltmeter leaky? It should only "draw" a charge, not a current.

BTW I don't want my wasps fried, because then the spider to which I offer them is not interested. They have to wake up and flutter, then she swoops and bites...

I'm not familiar with electrostatic voltmeters. I bought it as an antique and was surprised it works. A normal voltmeter draws current does it not?

It's amusing when the spider goes to get them and gets zapped too.

Anyway I'm going to go with power, 5W. That's enough heat to fry an insect.

It's energy, from a capacitor, not current that kills bugs.

The cap charging current is likely microamps.

Since when I unplug the USB cord, the voltage drops to 0 instantly, I doubt there's a cap in it.

The mains one is just a 240V to 2000V transformer directly connected to the rails.

It wouldn't be hard to measure. Or google.

That sounds lethal to bugs and to humans. And a fire hazard.

One outfit that I work with considers 9 joules the be the human threshold of death. I'd guess that 1 joule would take out a mosquito.

These devices used to make a loud noise as they discharged a capacitor into the insect. This is no longer considered a good idea because if the insect explodes too violently the bacteria-laden fragments are dispersed over a wide area. It is much better just to cook them without fragmentation. I did once come across a standard for such devices - I will see if I can find it. John

The 'transformer' may be a potted circuit, with current limits like in a neon transformer. It won't be tightly line-coupled like an ideal power transformer.

The human threshold has to do with heart-stoppage; the insect lethality is more about heating ( boiling temperature rather than fever). You can't bollix the circulatory system of an insect, because it's mainly just diffusion.

Bacteria-laden fragments over a wide area? From a mosquito whose total mass is a few milligrams?

Sure must be peaceful where you live, if that's the biggest worry. ;)

Cheers

Phil Hobbs

From what I remember of the one we had in our physics department at college they measure the electrostatic attraction between a pair (or multiple pairs) of plates connected to the input. So the whole thing is a capacitor of variable value, because the plates move in relation to each other. Thus the only current flow should be that needed to charge up that capacitor. (Unless there is leakage.)

I'd rather a mosquito go POP 10 feet away, than it being smooshed against my arm after it bit me.

The bug zapper schematics that I can google are mostly a tiny blocking oscillator driving a step-up flyback into a capacitor. Must be milliwatts into the cap.

I used a screwdriver. It's a cap, and a tiny transformer with a transistor and some passives. I guess it discharges through the safety resistors very quickly, which means there won't be much jolt in it for the insect.

It's a proper insectocutor (the biggest well known make). How can it be a fire hazard when it's contained?

It's great fun to watch a wasp getting fried. It f****ng stinks though.

That would be why the decent one I have fries them gently, while the cheap Chinese USB one uses a capacitor.

The insect when not killed is presumably spreading that bacteria on food anyway.

Why are they no longer made like that? Digital ones use a fair amount of current which is annoying in some circuits.

Any 60 Hz transformer that makes kilovolts is going to be huge. Loose coupling and potting make them huger.

The old neon sign transformers were huge; the modern one are high frequency oscillators. The old ones looked nicer for some reason.

When I was a kid I had an infinite supply of used neon sign transformers. Fun. The double-ended 18 KV was my favorite, but it must have weighed 20 pounds.

The old oil-filled car ignition transformers were cool too, driven from an oil cap through a thyratron. 3" sparks.

Mine gets warm. I'm guessing it uses a lot of the 5W rating all the time. I can send a photo of the circuit if you want.

Only huge if high power. Mine is about 1.5 inches x 1.5 inches x 1.5 inches.

The light output or the circuit looked nicer?

How many friends did you torture with it?

Could you kill someone with those? I've been told that contrary to popular belief, the "modern" ones from the 90s (pre electronic ignition) didn't have enough current to kill you. I heard of one mechanic grabbing one, he couldn't let go but he was unharmed.

and ignition coil is a few 100 mJ, a defibrillator is 1000x that

Speak for yourself. Where I grew up, the mosquitoes were as big as chickens.