Fly electrocution racket: I want lightning and thunder

[tgm1024]

Ok, we have one of those electrocution wands. 1.5v. Looks like a short badminton racket with wires interleaving across it--touching any two neighboring one shorts through the fly.

I can hear the cap whine up. But nothing discharges unless I'm continually feeding it from the battery by holding down the button. And this is what happens (this didn't happen with prior one):

fly hits it
spark
fly drops to floor
gets up, slaps his head, says OYE, and flies off with a headache

First of all, what is happening here? If the capacitor is "dead", doesn't it just short and if so, why would it spark at all, and why the whine? <----I'm obviously ignorant of how capacitors die.

2ndly, if the fly is being fed from the battery alone through the cap, would the VA driven through it spark when only 1.5v?

3rd: assuming there's a 1.5v capacitor in there. If I fed it with 3v, does that just burn it out or allow it to discharge more?

What would be the quickest set of steps (sans buying another one) that would educationally allow me to fix and modify this thing?

THANKS!!!!!!!!!!!!

 

[(*steve*)]

1) A possibility is that the capacitor has gone open circuit, or is very low in capacitance, or doesn't exist (to save money). Is it made in China?

2) Measure voltage and current at the 1.5V battery when operating and multiply them together. Divide that by 2 to allow for inefficiencies in the circuit.

3) Either or both.

4) Open it up, see if there's a capacitor there and add one or replace the existing one. You may have to guess at the voltage rating and the value of capacitance, then measure the voltage and try it out to see if the capacitance is acceptable (i.e. charges fast enough, kills flies)

Remember that it may not be as simple as I have described

An interesting factoid is that these devices are so hugely dangerous that Australian Customs mentions them explicitly as a forbidden import. (No, I'm sure they're not that dangerous)

 

[LTX71CM]

It could be your battery is low or has poor capacity. If it's a battery that came with the zapper that's most definitely the case.

The whine is probably from a high voltage charging circuit that takes 1.5VDC and steps it up to a couple hundred volts for fly zapper. Much like the circuit you'd find in a camera flash.

I don't see a problem with having to hold down the button. If you don't think you're supposed to or if the directions say it's not necessary perhaps the capacitor is very "leaky" and should be replaced. The zapper will not store a charge for later use I don't suspect. Wouldn't be very safe if it did. Read: Curious children.

 

[LTX71CM]

A quick Google search just turned up this page, complete with schematic.

http://www.electro-tech-online.com/...cket-shock-device-replacement-components.html

 

[Militoy]

.....

The whine is probably from a high voltage charging circuit that takes 1.5VDC and steps it up to a couple hundred volts for fly zapper. Much like the circuit you'd find in a camera flash.

......

Actually - more like a thousand volts. I have a chinese - made one that actually works pretty well. I don't expect it to last very long - but it didn't cost much, so no worries. Mine will actually burn a spot onto a paper clip bounced off the grid. Loads of fun when a fly has the impunity to enter my office...

 

[tgm1024]

A quick Google search just turned up this page, complete with schematic.

http://www.electro-tech-online.com/...cket-shock-device-replacement-components.html

Interesting. It is also a good example of an OP keeping calm in the face of a rude pedant. Being told to grow up if he's a kid and side stepping that is fairly impressive to me.

 

[tgm1024]

1) A possibility is that the capacitor has gone open circuit, or is very low in capacitance, or doesn't exist (to save money). Is it made in China?

(Yikes---ignorance storm in me 'ead) If the capacitor has gone open circuit, wouldn't that mean that it is effectively at infinite resistance disabling any current flow at all, fly or no? The fly zapper does zap, just hardly anything, and does not hold a charge waiting for discharge like it's supposed to.

Also, do such voltage ramping circuits without a capacitor make a whine like that? I thought that was a surefire indicator of a capacitor.

 

[(*steve*)]

The capacitor stores the charge.

Think of the current as a small stream, the capacitor like a dam, and a fly opening sluice gates when it makes a circuit. Without the dam, the trickle of water won't do much harm, but add a dam wall and the water builds up, gushing out destructively when released.

In this circuit, having the capacitor go open circuit is like not having a capacitor at all.

The whine is from the transformer. The transformer creates an alternating magnetic field and anything that is slightly moveable and affected by that magnetic field vibrates at this frequency. It's not desirable, and represents a slight loss of power, but it's very common. Indeed it is why such devices are operated at frequencies outside the range of normal human hearing.

 

[(*steve*)]

Interesting. It is also a good example of an OP keeping calm in the face of a rude pedant.

Funny, I saw it as the blind leading the blind...

I struggled to find any worthwhile advice, and the errors in the circuit diagrams were not noticed (or commented on) by anyone.

Having said that, you can glean some useful information from the circuit diagram.

 

[tgm1024]

Funny, I saw it as the blind leading the blind...

I struggled to find any worthwhile advice, and the errors in the circuit diagrams were not noticed (or commented on) by anyone.

Having said that, you can glean some useful information from the circuit diagram.

No, the validity of the information is not what I'm talking about. The OP may have been "blind", but he remained polite at an overt slap in the face.

 

[tgm1024]

The capacitor stores the charge.

Think of the current as a small stream, the capacitor like a dam, and a fly opening sluice gates when it makes a circuit. Without the dam, the trickle of water won't do much harm, but add a dam wall and the water builds up, gushing out destructively when released.

In this circuit, having the capacitor go open circuit is like not having a capacitor at all.

Ok, Thanks, your meaning is clear.

For my own edification, can you clear a small thing up? I must be thinking of the different use of open and closed: "Closed" is when a circuit can complete. Open is a broken circuit with nothing flowing.

What would they mean here then?

http://www.repairfaq.org/sam/captest.htm]

For electrolytics in the uF range or above, you should be able to see the cap charge when you use a high ohms scale with the proper polarity - the resistance will increase until it goes to (nearly) infinity. If the capacitor is shorted, then it will never charge. If it is open, the resistance will be infinite immediately and won't change.

 

[NickS]

Well the fact that it builds enough charge to arc across the fly says the step up is working. The fact you have to hold it on may be safety but it may also just be the mfr cheaping out and not adding an output capacitor. The fact that the fly survives seems to lead me to believe poor design. If there is an output cap then you need to bump up the capacity on it to store and deliver a more lethal amount of wing torching current. If there is no output cap then you could try adding one. I would suggest a HV ceramic disk cap rated for perhaps 3kV and 10nF for starters.

But to answer your question about caps... voltage is all relative. I may be sitting in a cloud that has a charge in excess of 100kV but in reference to what? if there is no good reference point then there is no action. So if your cap is open then one or the other lead may be tied to a ref voltage but it will not store any usable charge because the capacitance has dropped to nearly nothing. but with the cap intact and tied between a high and low voltage then it can store charge proportionally to voltage difference
>> Charge = Capacitance*Voltage(across leads).
So to review opening the capacitor drives the capacitance to zero thus charge to zero.
shorting the leads drives the voltage across leads to zero thus charge goes to zero.

Does that make sense?

 

[tgm1024]

[...] opening the capacitor drives the capacitance to zero thus charge to zero.
shorting the leads drives the voltage across leads to zero thus charge goes to zero.

Does that make sense?

Perfect. Thanks!

Is the capacitor wired in parallel to the grid so that an open capacitor doesn't break the circuit?

 

[NickS]

Yes an open cap does not break the circuit but it does stop charge from building up.

Think of it as a 50 gallon drum of water which you have hoisted up 10 feet off the ground to dump on an unsuspecting victim. Having a fully charged working Cap is like saying the drum is full of water. And having a broken cap it like saying there is 1 cup of water in it. That cup of water is still 10 feet off the ground but it is pretty unimpressive. Like what the fly you hit was saying("is that all you got")

 

[Militoy]

....
But to answer your question about caps... voltage is all relative. I may be sitting in a cloud that has a charge in excess of 100kV but in reference to what? if there is no good reference point then there is no action. So if your cap is open then one or the other lead may be tied to a ref voltage but it will not store any usable charge because the capacitance has dropped to nearly nothing. but with the cap intact and tied between a high and low voltage then it can store charge proportionally to voltage difference
....

I'm trying to build a picture in my mind, of you sitting cross-legged on a cloud, Nick...

As a note - my own "fly-zapper" has never held a charge - even when fresh from the factory. You have to hold down the button for it to work - and as soon as you release, no more arc on the paper clip. The quick bleed-down is probably an intentional safety feature.

As a rabbit-trail thought - I have noticed that some flies seem particularly aware of the 13 KHz whine of the zapper. As soon as the button is down - they are suddenly no where in range. Thanks, Pavlov!

 

[Resqueline]

Some of these zappers can only kill moskitoes, others can almost do in hornets. All have some bleed-down resistor, on some it is switched in as you release the button.
They can often be slightly modified to give a little higher voltage & a stronger zap. There's usually a space limit so it can be hard/impossible to fit a bigger capacitor.
If you have a picture or two of the thing then it might help us give some specific advice.

 

[tgm1024]

I'm trying to build a picture in my mind, of you sitting cross-legged on a cloud, Nick...

As a note - my own "fly-zapper" has never held a charge - even when fresh from the factory. You have to hold down the button for it to work - and as soon as you release, no more arc on the paper clip. The quick bleed-down is probably an intentional safety feature.

As a rabbit-trail thought - I have noticed that some flies seem particularly aware of the 13 KHz whine of the zapper. As soon as the button is down - they are suddenly no where in range. Thanks, Pavlov!

Continuing that rabbit trail...Actually, that would be Darwin, not Pavlov unless we're talking about non-lethality. I've also noticed a similar effect.....there just isn't as much road kill as there was when I was a kid.

Perhaps that's the effect of things being less rural now, but I don't think so...even when I visit EBF Maine. When I was a kid in NH there was a clobbered chipmunk or squirrel speedbump every quarter mile. I think over the many generations, only the ones that avoid the traffic (or look both ways or jump up to hit the walk button) survive.

 

[tgm1024]

Some of these zappers can only kill moskitoes, others can almost do in hornets. All have some bleed-down resistor, on some it is switched in as you release the button.
They can often be slightly modified to give a little higher voltage & a stronger zap. There's usually a space limit so it can be hard/impossible to fit a bigger capacitor.
If you have a picture or two of the thing then it might help us give some specific advice.

I would LOVE to do just that, but as [bad] luck would have it, the thing slipped out of my hands yesterday and shattered all the wires out of the frame. There's another one arriving tomorrow. My kids (4 and 6) are practicing their maniacal "mwa ha ha ha haaaaa" laugh.

 

[Mitchekj]

... I read "Fly electrocution jacket."

Now that would be interesting!

 

[(*steve*)]

... I read "Fly electrocution jacket."

Now that would be interesting!

Hey, perhaps you could build one into something like this:

It sounds a lot more high-tech than this: