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Forum Index : Electronics : Bug Zapper
| Author | Message | ||||
gyrogearloose Newbie  Joined: 02/09/2011 Location: AustraliaPosts: 11 |
I need to create around 3000 volts Dc from 12 volt battery, tried several ways to do it but as the voltage increases the amperage diminishes to a point where there is no heat left to do the real damage. I watched a small black beetle cross the grid with a small zzzz and a puff of smoke and the rotten thing kept right on walking then flew away. Apparently there is not enough moisture in them for the current to pass though. Any ideas? Tony Gyro-Gearloose |
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| MOBI Guru  Joined: 02/12/2012 Location: AustraliaPosts: 819 |
@Tony, A "Bug Bat" from Bunnings for about $5 or the like might be a good start - however, even with those, a fly needs a few zaps to conk it. Beetles are even harder to kill. As you say, not enough moisture in them and being exoskeletal, their organs don't get affected. Daddy Long Leg spiders can cook up almost all their legs and still keep going. Best of luck David M. |
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trash Newbie Joined: 18/02/2014 Location: AustraliaPosts: 6 |
Ok, lets assume that you know the dangers of playing with high voltage and high current. I'm wondering what several ways you have 'already tried' to get to 3000VDC ? The reason why you're not getting enough current is... well the laws of thermodynamics :D The universe demands that you pay your power bill up front. Lets just go with the black box approach. You have a magic black box. You connect 12VDC to one side and 3000VDC comes out the other without knowing what is inside. We'll assume at this point it is 100% efficient. 3000/12=250. This is the voltage gain. Power in = Power out, so you will have a current loss of 250 to pay the universe back. If your black box has an input impedance of 12 ohms it draws 1A and the output current will be 4mA. (less with any real world power loss). It's not a lot of current, but it's more than enough at 3000VDC to do some damage. If you get caught across it, well you're not going to forget it in a short period of time. But lets assume that you have calculated that you NEED 50mA. Getting this as a constant DC voltage just isn't going to be practical. The only way to do that is make the circuit bigger so that it draws more current at 12VDC. That may not be practical. However, you know how bug zappers work and they don't need a continuous current at High Voltage. Just a short burst of a fraction of a second is enough to vanquish the average insect. A pump charge circuit can be built. Basically a high voltage capacitor is charged at 3kV. After about five time constants it's fully charged. When a short circuit or low resistance path is presented to it, a huge amount of current will flow with an EMF of 3kV with respect to the load resistance and time to discharge. Naturally a charged high voltage capacitor is a very dangerous little item. It's not uncommon to hear of people turning off their circuit thinking that the capacitor is discharged and feeling the 'touch of god'. For that reason alone it is wise to install a 10M bleeder resistor across any HV caps before you even start. Ok... down to the nuts and bolts. You can convert the 12VDC to AC and then step it up with an ordinary transformer. It's old school and not very efficient. A flyback coil like a car ignition coil, TV flyback transformer etc should get you to 3kV probably 5kV without too much hassle. A high frequency high voltage diode would then supply the HV to your capacitor. I'd use this kind of set up if I was looking for trouble. It's big and clumsy and could hold back a bull elephant. Normally, I'd build my own flyback circuit and run it at high frequency to make the flyback transformer small and light. A disposable camera flash circuit is pretty much the same circuit and I find it very easy just to cannibalise them for any small HV power supplies I need. They're not exactly suitable for your task because they only pump the HV capacitor to about 300VDC. But they're well worth studying for this exercise. Another similar and more useful circuit is a CFL power supply. You can rip them out of any old flat screen TV, but I find it easy just to buy them from jaycar or ebay etc. Under load you give them 12VDC and they produce about 150VAC to drive the tube. However, if they are unloaded, they will produce as much as 1kVAC. This can then be used to drive a Walton-Cockcroft multiplier and multiply the voltage up to 3kVDC or higher. The final capacitor then acts as the charge reservoir. (Again, with the 10M bleeder resistors for all the HV caps) So as long as your careful how you load up the circuit it only takes a couple of seconds to charge the HV capacitor. I'd suggest going to a higher striking voltage and then when the current is flowing through the bug a lower voltage cap with more current finishes the job. A CFL power supply with Walton-Cockcroft multiplier with a correctly place charge capacitor is ideal for the job. VK2XSO Yes I am an agent of Satan, but my duties are largely ceremonial. |
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| gyrogearloose Newbie Joined: 02/09/2011 Location: AustraliaPosts: 11 |
Hi Trash Interestingly I found a real beaut unintentionally! I was asked to fix a flasher on one of our forklifts and found the tube in it blown. Putting 12 volts across it and shorting the remnants of the tube with my screwdriver i got quite a spark. Taking it home and putting it on my trusty old oscilloscope I found it delivered just over 4K and putting a beetle across it instant fry. Pity it is all bonded with some sort of polymer all that is visible is the top of the big capacitor. It does however consume my 12 volt 7 amp hour gel cell too quickly so I'm looking at finding a way to stop it using so much current once the cap is charged. Regards Antonius Gyro-Gearloose |
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| trash Newbie Joined: 18/02/2014 Location: AustraliaPosts: 6 |
One of the most useful tools you can have working with HV is an eletrostatic voltmeter. They have a very high impedance and don't load down the circuit. I'm guessing you're using a big voltage divider to check it on your scope. The simple way to limit the output current is just with a resistor on the output. correction, I misread that and I can see you want to stop the charge pump once it's fully charged. I'd look again at the current it draws at 12VDC and see if it drops off dramatically once the capacitor is fully charged. You may find the most efficient way is just to keep pumping that capacitor to keep it charged. You can always put another capacitor external to the circuit. Use a very low leakage high voltage capacitor for the job and isolate it from the pump capacitor with a HV diode. Using a very high impedance voltage divider like you use on your CRO use it to drive a simple JFET which turns a relay on/off to turn the 12VDC off. The leakage current of the voltage divider will become the factor determining how often the circuit turns itself on. VK2XSO Yes I am an agent of Satan, but my duties are largely ceremonial. |
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| Goeytex Regular Member  Joined: 12/05/2014 Location: United StatesPosts: 74 |
Check out the LT3750 Capacitor charger IC. It can charge any size capacitor up to about 500V. Uses a very small off-the-shelf ($5.00) flyback transformer from Coilcraft, Wurth or Murata. Charge a high pulse current type cap up to about 100V, then discharge the cap through a step up transformer. A 4uf cap can be charged to 100v in about 1 ms or less depending upon components selected. Glue logic can be done with any micro-controller. Bill |
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Tim_the_bloke Senior Member  Joined: 15/11/2009 Location: AustraliaPosts: 105 |
I have a tennis racquet style mozzie zapper, powered by 2 AA batteries. It certainly stops mozzies, moths, etc. Some big flys seem to be too round to make contact with the inner mesh and may survive first contact, but once they short the mesh layers there will be a flash and burning smell. One night I left it on my bed, later in the dark I laid my forearm across it and must of somehow pressed its button. I can attest it gave me an instant wake up, and I won't be doing that again! |
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Dave Newbie Joined: 01/02/2015 Location: New ZealandPosts: 5 |
Check out something like this: http://www.aliexpress.com/item/Menton-case-for-DC-3-6V-6V-To -400KV-Boost-Step-Up-Power-Module-High-Voltage/32271291159.h tml This is a 6v to 400kv (or so they reckon) model but a quick search there will reveal higher-spec models that will really dazzle. On this one just put a couple of LiPo batteries or a 6v power supply on the primary and watch the light show. Connect to a micro-switch and your grid and I'd imagine even the beetles will do a little dance... Dave. Dave T. Christchurch, New Zealand. |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
link in above message it does not appear to work  Klaus |
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| Dave Newbie Joined: 01/02/2015 Location: New ZealandPosts: 5 |
Sorry about that Tinker, seems a space or two crept into the link. In fact, it appears the forum adds spaces to long links and can't cope with them, though when the link button is used the link is displayed with gaps but does in fact work so the following link should get you there. http://www.aliexpress.com/item/Menton-case-for-DC-3-6V-6V-To -400KV-Boost-Step-Up-Power-Module-High-Voltage/32271291159.h tml You can also copy and paste the link but note there is a space added by the forum between the To-400KV part of the link and the html suffix. If you take those spaces out it works. Alternatively just visit www.aliexpress.com and do a product search for Step Up Power Module High Voltage Generator and you'll get hundreds of hits. Be warned though; if you haven't been to aliexpress before be prepared to spend hours on that site and keep in mind you may end up spending all your income on the gadgets there! Please note I am not affiliated with aliexpress or get any rewards for sending people there; I am aware most forums don't allow advertising links and I wouldn't have mentioned this site at all if they didn't sell something the OP was asking about. Dave. Dave T. Christchurch, New Zealand. |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
The adding of spaces is a deliberate thing for prevention of scams or something. You will find it much easier if you use the editor's LINK button. It's the 4th from the left with a globe and a chain link. |
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| Dave Newbie Joined: 01/02/2015 Location: New ZealandPosts: 5 |
Thanks for confirming my suspicions there BobD - I did use the link button and as I pointed out, the link as-displayed still has gaps but the underlying html is valid so the link will work. Kind regards Dave T. Christchurch, New Zealand. |
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