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I decided to write some instructions for constructing a high voltage ignition system for a combustion cannon.
Before I go any further Ill just give the usual disclaimer.
-This project deals with high and potentially lethal voltages, the main capacitor has enough charge to deliver a painful shock, after it has gone through the spark coil the voltage is increased to anyware from 20000 to 75000 volts, probably with enough current to do some damage.
-The capacitor will retain it's charge for quite a long time even once the circuit has been switched off.
-If you are new to working with electronics, or are unsure about working with high voltages do not attempt this, or get someone else who is, to help you.
-Do not adjust wires or anything while the system is charged up, always turn off and discharge.
-I will not be held responsible for any damage or injury caused by this device.
Ok, this project uses circuits from disposable flash cameras. If you don't have any of these then go to a photo developing store and ask for some used ones, they should give you some for free.
Different cameras have different circuits but they all do basically the same thing. As long as you can turn it on and off and it charges up the capacitor then you're sweet.
The circuit I have used is from an older Fuji brand disposable. Not sure if their still around but they might be, I use it because it is the most simple and easy to work with.
It's quite simple how it works. All your doing is charging up the main capacitor to about 330 volts, then using a SCR (Silicon Controlled Rectifier or Thyristor) to discharge the capacitor through an ignition coil.
This boosts the voltage to an extremely high level, enough to make a spark. The advantage of the SCR is that it is solid state, it will never ware out and operates efficiently and safely.
The SCR is trigged by a switch connected to the capacitor and a high value resistor. After it has discharged it will charge up again and so on.
Originally there is only one cell used to power the circuit, I have used 2 AA size cells in series to produce 3 volts. This makes the circuit charge faster.
In doing so though, I have to replace one of the resistors with one of a slightly higher resistance to limit current to the transistor. Although it should work without doing this I like to be safe as I have burnt a few of them out by drawing too much current.
-One SCR, I used a "TYN816" It has an 800volt limit and 16 amp (continuous) 200amp (surge) limit. Plenty for this application. It cost around 5 bucks. I bought it at "Dick Smith Electronics" in New Zealand but any electronic hobby store like Radioshack should have them or be able to order some in.
-2 AA battery case with switch. The inbuilt switch just simplifies things. You would just add your own switch if putting this in a custom case of some sort.
-Push-on Pushbutton switch.
-Lengths of wire for connecting the triggering switch and some that connect to the ignition coil.
-33Kohm (33000) ohm Resistor
-390ohm Resistor (optional)
-Soldering iron and solder. (and a solder sucker if you got one) You need to be pretty handy with a soldering iron to make a good job of this project.
Although this post deals with one type of camera flash circuit. The SCR and triggering device can be added to ANY camera flash circuit out of a disposable. Just connect the appropriate leads to the positive and negative sides of the main capacitor(330volt@100-160µF).
Once you have built it, before you turn it on check to make sure nothing is going to short out. Check the legs of the SCR especially, covering with heatshrink tubing helps. Check that you haven't accidently soldered two different pads together and that there are no dry welds.
When you turn it on, most likely you will hear a faint high pitched whine as it charges up. When it is fully charged the built in neon light or LED will start to flash indicating its ready.
You don't need to use a car ignition coil for this, if space is limited you can use one off a lawnmower engine or a go cart engine, ofcourse the size of the spark will be smaller.
Feel free to ask questions..
Now some pics
Last edited by nz_cannons on Sat Oct 06, 2007 6:46 pm, edited 3 times in total.
Wow, that is great tutorial. That thing can put out one seriously long spark. And the circuitry isnt too messy like other ignition systems. Good job
Airbeds... so many different uses
The SCR is not needed if you don't mind that the flash actually still flashes. You can just use the flash board's trigger coil and the Xenon flashtube instead. Simply wire the flashtube in series with the automotive igntion coil. Functionaly, the flashtube is identical to the SCR except it takes a much higher voltage to trigger (which is already present on the photoflash board).
It seems to me that using the flash would be wasting some of the energy.
Using an SCR means that all the avalible energy in the capacitor is discharged directly into the ignition coil, instead of being converted into light.
After using the flash, the capacitor is discharged, so how much would be going into the ignition coil if it were connected. My theory anyway..
Yes, the flash probably does waste some energy, but not enough to make much difference. The SCR also wastes some energy, as heat mostly (which is why it has a built in heat sink).
Nothing wrong with using the SCR, though finding one with high enough ratings isn't all that easy. Even if you can find the SCR for $0.50 it's liable to cost $5 to ship it.
Lets see from Mouser (a common electronics supplier) the TYN816 is US $0.79 each in small quantities. Cheapest shipping from Texas to Indiana is $5.85. Of course, the $5.85 would cover the shipping of a bunch of other stuff in the same order.
Digikey has them for $1.50 each, with $4.60 for shipping plus an extra $5 for orders less than $25.
I can't find any SCRs on the Radioshack website, which is surprising.
All Electronics currently doesn't list any high power SCRs.
So, if you can find a suitable SCR, and if have the $$$, and the patience to wait for shipping, then it is a great approach.
If you are impatient, or don't want to spend $6 or more for the SCR, then just wire the coil in series with the flash tube.
Hey NZ cannons I'm from NZ too. Great tutorial its been lots of help. I've bought an ignition coil off TradeMe and it looks right for the job. It says however on it that "ballast resistance is required" and I don't won't to test it in case it screws everything up. Will it not work in this circuit without "ballast resistance" or am I just paranoid?
Here's the coil: http://www.trademe.co.nz/Trade-Me-Motor ... es/Parts-O ther-makes/Electrics/auction-136806356.htm
I also saw a small coil for a quadbike though again I'm not sure if it'll work:
http://www.trademe.co.nz/Browse/Listing ... =136382032
Yeah that car coil looks pretty standard huh, should just be able to connect it up and it should work.
The ballast resistor is for when it's in a car and is used to regulate the voltage/current so as not to overload the ignition system, but in this circuit we want the opposite essentially.
I have never paid for a coil, you should just go to an auto wreckers and ask if they have and old coil lying around, they will probably give it to you for free. Or find an old dumped car somewhere and pull on out.
The quad bike one looks ok except the main high tension lead (the thick black one) is bad for this kind of thing as it has a high resistance, if it can be removed thats good but if it can't then its pretty useless. I wouldn't bother with it.
Also, how long does the ignition take to charge when it has been modified to use 2x AA batteries and a 390 om resistor. Normally it is about 3-4 seconds with 1x AA so is 2x something like 1-2 seconds or instantaneous?
Sorry for all the questions but how do you wire 2 ignition coils in anti parallel? Could you provide a diagram? Does it provide much of a boost to the spark? And also are these types of ignitions suitable for wiring multiple spark gaps?
hey there i had your ignition up and running fine but i just decided to get some AA energizer lithiums so it would run good for ages. it then worked a couple of times but then it stopped charging and something started smoking and now it doesn't work. is it possible the batteries were too good? i can't figure out what has screwed up so do you have any idea what could have happened and how to fix it?
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