High Voltage Generation

Hello,

I want to build a mosquito trap at home as an experiement. I plan to used a plused ultraviolet light source to attract the insects and surround the light tube with a copper wire mesh.

However, I need to generate atleast 1500V to 2000V for the same to be really effective. Unfortunately, I am not able to buy high voltage capacitors due to unavailability in the local stores. Thus I cannot design a voltage multiplier using the standard diode-capacitor multiplier circuit.

However, at one of the shops, I saw the TV fly back transformer and this idea hit me. Can a FBT be used to get this higher volts. Need some tips/expert guidance to design .

1. Whats the easiest way to generate high voltage ( atleast 2KV) using an FBT. Switched DC or even sine wave output is OK too.
2. Is it necessary to have a switching circuit in the primary as its in a TV ? If its a transformer, can it be fed directly from the 230V main ( with proper current limiting ) and get higher stepped up voltage at output ?

It's a high frequency transformer, you can't feed mains to it - it's also only low current, usually the insect killers just use a high voltage transformer.

Nigel
Thanks for the reply.

However, if its a high freq transformer, what stop's one from feeding it with low frequency ? may be it would saturate the core. would it ?

Anyways, i would still need help to take this further as for me, a FBT is available for about $3 but i may not be able to get a proper high voltage transformer even for $50 and may be its not available too.

I could easily design a 555 to generate 15K pulses and switch a BU508 king of a switching transistor across a rectified mains sine wave.

Would it do ?

manoj.patil.1974 said:

Nigel
Thanks for the reply.

However, if its a high freq transformer, what stop's one from feeding it with low frequency ? may be it would saturate the core. would it ?

Click to expand...

There would be a large BANG!! and the transformer would disappear!!!.

Anyways, i would still need help to take this further as for me, a FBT is available for about $3 but i may not be able to get a proper high voltage transformer even for $50 and may be its not available too.

I could easily design a 555 to generate 15K pulses and switch a BU508 king of a switching transistor across a rectified mains sine wave.

Would it do ?

Click to expand...

You could try it, but the current output is very low (only about 1mA), and it needs accurate tuning and loading - I'm not hopeful!.

Hmm...

But if 20mA is enough to kill a human brain/heart, wouldn't 1mA enough for mosquitos ? Mosquitos are only my target AND no other larger insects.. not even the houseflies.

manoj.patil.1974 said:

Hmm...

But if 20mA is enough to kill a human brain/heart, wouldn't 1mA enough for mosquitos ? Mosquitos are only my target AND no other larger insects.. not even the houseflies.

Click to expand...

Do you think the electric chair only uses 20mA? - and it only seems to kill quite slowly, and that's with excellent connections to the body.

Try it and see - but commercial ones use a mains transformer, and a LOT more than 1mA.

OK

So what is the min voltage and min current enough to kill a mosquito by guarentee. ?

May be this will help me with the design. If lower voltages could help kill by gurentee , then FBT need no be necessarily used

manoj.patil.1974 said:

OK

So what is the min voltage and min current enough to kill a mosquito by guarentee. ?

Click to expand...

No idea?, try checking what commercial units use.

May be this will help me with the design. If lower voltages could help kill by gurentee , then FBT need no be necessarily used

Click to expand...

The insect killers I've seen don't 'electrocute' the insect, they 'fry' it - putting so much current through it's body it burns!.

Well consider that the correct thinking is in the realm of energy "to kill", to be more helpful. The unit ofcourse is 'joules'. It takes, off the top of my head, 15-50 joules to do the hapless soul of a person into the unkown. Ofcourse this is mitigated by the time that energy is delivered to that 'hapless soul'. (however in the case of electrical zaps these numbers are roughly correct) Considerations of the current to the driving voltage define this "energy". So at 10mA with a driving voltage of 2000V, you will deliver 20W. Each spark generally commutates at around 100usec. A watt is a joule a sec. So, you will have delivered in the neighbor-hood of .002 joules. This is 133 millionth the energy required by a human at the low endof the spectrum. A misquito, by quick look on the internet denotes a weight of 2.25 millionths of a pound or about 400 millionths the weight of a human. This gives your spark roughly the 3 times the potency by comparison to the human DOA instigator.
In thought, here, but not necessarly to a comprehensive one, one would think that they would need something to partition the voltage "sparks". If you consider that the mosquito is completing a circuit in some sense. i would make sure that the circuit has some method of regulation, less one finds his "sparker" sparking till the FBT says it's had enough. Hope this helps.....

-this reply was written in the interest of scintillating and substinative thought....and hopefully discourse.

....also if this if this lends some length of doubt. One can safely relegate himself to the numbers and perhaps operation of an engine ignition system. Not enough to be but of superficial harm to a person, but certainly enough of perturbance to the fluttering little heart of a mosquito. Consider numbers such as 30-35kV with 100-300millijoules with a commutation time of around 1-2 milliseconds.

Use a neon sign transformer, it's both high voltage and current limited.

In my commercial zapper, the transformer is 4kV @ 6mA. As Nigel says you need to fry them otherwise the first one that dies shorts the supply.

BTW, I bought mine for Au$80 (£30). I think you would be hard pushed to build any mass produced item these days, cheaper than you can buy it.

Mike.

I would think the real trick is not generating the high voltage but rather designing the target screen. Having the flying bug just coming in contact with a high voltage screen would not do anything would it? Doesn't the insect need to make contact with both the HV and common return? Does that mean the 'screen' needs to be interwoven with both PS terminals spaced not to generate sparking on it's own but only if the insect becomes in contact with both + & - screens? Sounds like a difficult construction project unless copying a know design.

Lefty

They don't need to come in contact, just fly between them - this lowers the 'resistance' enough for an arc to form.

Nigel Goodwin said:

They don't need to come in contact, just fly between them - this lowers the 'resistance' enough for an arc to form.

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I understand that, but that means there is a certain mechanical spacing required between the high voltage screen and a common screen or cylindrical plate carrying the opposite potential, right? Not just a single wire going to an insulated wire mess screen would work? This is the part of the design that I think requires some effort or working from a known design.... The bug has to somehow find itself between two potentials for anything interesting to happen



Lefty

mechanical design should be easy. I could take two bare copper wires and then wind them around the ultraviolet lamp in a coil like fashion from bottom to top. The two wires would separated by a distance not to form an arc, but no too much for the mosquito to just fly away.
If this does not work, i may use the simple tennis racket kind of mesh (two of them)

hey if you just want to make a circuit why dont you see my post "circuit problem"?? I've posted a circuit picture and also i've decoded it. so if you are trying to build one, refer it. you can even contact me. I'm also doing the same circuit dude!! I'v nearly reached the final step. May be we could work together.