CDI help (electricians needed!)

Ok.. the CDI won't spark continuous, but as slow as the human eye works, it can look continuous after it's firing at least 20 times per second or faster... How do you do this?
You make an oscillator circuit and your input leads to the CDI will go to the output of the oscillator circuit, you can uase it as a fixed value to look continuous or you can add a variable pot to the timer circuit to control the speed of the pulses if it needs to be slowed down for any reason.

I dunno if Radio Shack still sells these little project books, but you can most likely google some plans for an oscillator circuit that can run off a 9 volt battery, a 12 volt source, or a 6 volt source, or whatever power you have available... If you're lucky you might be able to find an electronics student who would be more than happy to build you the oscillator circuit...

20 000 volts..... maybe a cdi with just alot of triggers. best way to keep amps low maybe.

Thunderhead289 said:

so what I want to do with a cdi is attach it to a power source where I will have continuous spark. I know they are six volt systems, so would there be a way to hook a cdi to a battery where it would continuously spark? doesn't seem like it should be that hard todo.

btw this is not going into the engine, its for something different obviously.

Click to expand...

So what you want is a continuous spark plug arc?
You don't need a CDI for that, just a really big DC power source, like an arc welder set low.

if amps are much to high= to much heat.

12volt auto hid ballast maybe.
or a ballast from a 35-55 watt offroad driving light

just a second coil is my best guess. it was fire 50 times a second or more.

rpm divided by 60 seconds=rps

plus if our ignition is wasted spark then twice as many ignitions/second.

You are going to need a battery to drive it. There is barely enough spark energy from that little mag on a china girl to fire the plug in the engine.

A small battery & spark coil is all you need. it only needs to spark when you are adding fuel to the exhaust.

Here is a tutorial

http://www.liveleak.com/view?i=cf4_1414026047

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FFV8 said:

You are going to need a battery to drive it. There is barely enough spark energy from that little mag on a china girl to fire the plug in the engine.

A small battery & spark coil is all you need. it only needs to spark when you are adding fuel to the exhaust.

Here is a tutorial

http://www.liveleak.com/view?i=cf4_1414026047

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Click to expand...

Hahaha... Very Nice, but that's definitely one way to do it... the relay is a good mechanical way to pulse the power, but a 555 timer chip will do the same basic thing without any mechanical component.

Look up 555 timer circuits on youtube and you should find an easy to make pulse oscillator... anything above about 20 hz looks continuous to the human eye, but it can be run at 50 or 60 hz or even more depending on what you need.

I remember your early posts about trying to make a flame thrower exhaust and needing more fuel to do the job... Maybe running the pulse oscillator or a relay oscillator like in the video and injecting a small amount of gasoline or propane into the exhaust would give you the desired results.. The stock muffler or a straight pipe with a spark plug and additional fuel should get you a 5 foot flame at WOT

what you want is to have a hose running from a pressurized can of flammable gas (butane would work) into your exhaust tube. then put a glow-plug inside your exhaust tube close to the outlet for your gas. there needs to be a one-way check-valve on the gas line. this setup needs to be at a sweet-spot near, but not too near, the exit of the tube.

rig up a switch that has a toggle for the glow plug (connected to a battery) and another button that opens the valve on your pressure vessel. these need to be separate or timed so the glow-plug is lit well before the gas gets there.

if you do it right the opening for the flame gas would be on/off and opens at just the right amount to sustain a flame coming out of the pipe at half throttle.
once rigged up like that there will be a little too much gas for a steady flame when the engine is idling, and at full throttle it would go out.

if you want the fire to be nicer at lower throttle it will be even easier to blow out, if you get it running nicely at full throttle it might explode your pipe if your engine stalls.

but basically you want a gas like butane or propane because it shouldn't be able to burn on it's own inside the pipe, but will burn once it gets outside the pipe.


oh and also, you will probably need to build a custom pipe specific for this purpose, and most of the reason to do that it so the air coming out of it moves more steadily and streamlike than a normal exhaust, this will mean restricting it a lot without giving it any 'tuning' that might drop pressure moving down the tube. you basically want a very narrow straight pipe, probably with a baffle or two in it.

I would use a gas grill electronic igniter, my son and I built a potato cannon with the grill igniter for spark and it worked great.

the issue with such a small engine doing this is the huge difference in pressure when the engine blows vs. when its in-taking, at low rpm is will almost suck inwards on the exhaust. this will cause the flammable gas moving through the pipe to jump forward, then step back. this is a recipe for blowing the flame out, a glow plug will always be hot and be able to repeatedly ignite the gas in the pipe regardless of it's flow-state.
this will get you lit, the problem now become that it can be lit going the wrong way, this shouldn't be able to do any damage to your engine, and if your pipe it sturdy enough it will only cause a backfiring effect at low rpm. but it will be possible using a setup like this to have your flamethrower suddenly become a bomb. you can mitigate this by having the flammable gas enter the pipe relatively close to the end, but there needs to be a little space between the gas outlet and the glow plug (in theory the ideal place for the glow plug would be opposite the gas outlet and about an inch further towards the exit of the exhaust.)

this is why the exhaust doing the throwing needs to be customized to this purpose, that said it only needs to be narrow and solid, nothing too fancy.
if you can get a pipe that is fluted at the outlet, but plain tube for the rest of the run, without welded joints along the pipe anywhere but the flange, that would work perfectly.

for reference, the standard way of making these work for movies is to use dummy exhausts that are purpose built flamethrowers that work independent of the vehicle, using a small fan to push air through the pipe into a setup like the one I am describing. using a fan like that eliminates having to build around the air moving power of the engine, and ensures oxygen is inside the pipe before the propane is. because you are using engine exhaust to move the flammable gasses out of the pipe you have to rely on the oxygen outside the pipe mixing with your flammable gas/ exhaust mix as it leaves your pipe (hence why a fluted pipe would be best) if you try and mix the flammable gas with oxygen as it enters your exhaust you will either blowback into that tube making it not work, or fill your exhaust with burning gas moving the wrong way, this will blow up your motor.

Heck, just repurpose a propane torch and attach the end to your pipe if it's just a flaming special effect, their starter is just a crystal.

supposedly, you only need a pyrotechnics license to operate a real military flamethrower.

Keeping a 555 alive with the nasty back EMF from an automotive ignition coil is no trivial task. The relay works just fine with the 250v spike on the coil.

Propane works, but so does gasoline. The Lowriders have been doing this for a long time:

30 foot flamethrower exhaust

How to install flamethrowers

No permit is requires for an actual flamethrower in the US.

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