Need a Circuit Designed

Capacitors (what would be necessary to do anything useful with this) will naturally discharge on their own, quickly or slowly depending on selection. You can get super capacitors that take months to discharge fully, but no matter what, the voltage will always be decaying. The trick would be to still have enough charge in it after your desired time period to still do whatever task you need it for (zapping bugs?). The problem is, the longer it would hold the charge, the longer it will take to recharge it, so you need to find a compromise with the recycle rate, i.e. how long until you want to be able to use it again.

This would not be a difficult thing to do but there are several things you must characterize. How much energy do you need to have available for the discharge to be useful in your application? Then you can determine how many cycles your 9V battery will provide. Careful parts selection in several areas would be the biggest challenge.

How much energy do you need and for how long, when you dischage?

If you are going to make a complite short circuit and for a very low duration then insteed of battery you should use capacitor bank. as typically done in magnetiser.

The charge would essentially just be enough to zap a small bug after holding the charge (and decaying) for a couple of days. So, the charge up may take awhile- that's ok, but it just needs to hold it long enough to provide a decent enough zap after a day or so.

Why not use the flash circuit from a disposible camera. You could remove the xenon bulb and hook the grid to those points. 9 volts will not make much of a zap, but the flash uses 1.5 volts with and oscillator across a transformer to build up to 330+ volts to store in the cap. Much better zap....Don't play with this if you are not qualified, for you will find the spark. A few D batteries in parallel should last as long as you need.

I believe we are off scale here. To effectively zap a bug you will need more than 300 volts unless you can get him to wet himself down and stand in a tiny bug bucket of water. Judging by the spacing on a standard bug zapper I would guess that you are talking about several thousand volts. You need about 1000 volts to jump 0.1 inch so do the math. The key elements are going to be the capacitor and the diode used to rectify the voltage you store on it. They will both have to be very low leakage. The reverse leakage of the diode becomes very significant in this scenario. If you are considering this as a home project it may be fine because you are not as concerned about the cost of the components. If you are thinking it could be a product you should first determine if there is a market and then whether it can be produced for a price that would sell. The parts cost would probably exceed that of a standard bug zapper but say you made it solar powered to charge a battery during the day it might fill a niche. Also you will want to use larger cells since 9 v batteries have a relatively low energy density.

I very much appreciate you insight. I like the solar power recharge idea, that could really work to keep the capacitor charged up. Is this something you can design?

Something like this is within the scope of my expertise and experience. However, this is my business. I only say that since it is not clear whether you are intending this as a commercial product or just a home project. But if you are serious about wanting to get it developed I'd be glad to discuss it with you further. If it's just a hobby kind of thing I can give you some general guidance but am limited to the time I could provide.

Think about a digital - big number counter to get pretty accurate time (24 hours?) to discharge a huge capacitor with low RC recharging and a clock generator. I did similar "flash ckt" several years ago that worked perfectly in my large Coulombs but low Voltage output. If your output should kill a bug, all above notes applied so you need to know exact killing voltage (even kiloVolts * 1.3 assurance factor) to produce desired effect. Start with the killing energy measurements before you will design and build a prototype.

Output voltage requires switching/toggle relay for two-state: discharge - recharge. Be sure contacts are sized for the equired output voltage!

I thought the bug would be the contact for a single use, new contacts with each new bug.

You might use a timer to turn on the recharge relay once a minute or so to keep the flash cap topped off.

Sounds like you need a stun gun with and an optical sensing device to close a switch. 30kV to 50kV in those things. Runs off a 9V battery too.

I'm not sure that it would be practical in terms of where the bug is but I do like the "out of the box" thinking! I think the output of a stun gun is AC so you would have to hit the bug at just the right moment which, although not un-doable, presents another design challenge.

Design for 9 volts, but make it capable of running off 14 volts. The thought I am having is in the case of RV's... 12 volt battery in your trailer... motor home... etc. 14 volts thinking of alternator output while charging the battery.