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Fireworks Circuit

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adanufgail

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I saw the other post on a fireworks igniter and all seemed slightly more complicated/complex than I needed. Besides, I went out and bought all my components already.

Based on my Honors Physics class lessons on circuits (about 5 days), I drew up a schematic and bought the necessary parts. However, upon putting them together nothing happened.

I've attached the schematic. The first switch is a shielded toggle switch like in a cool movie device. The second is a push-to-trigger button. The third wire is where the fireworks are attached. Normally, the firework would receive no current until the button is pressed, at which point it will receive nearly all the current. The only problem is that I do not have a 12V power source and don't feel like strapping 8 AA's together.

Thus, in scaling down the circuit, I came up with the equation that my resistors would need to be ~150 Ohms.

Sorry to beat around the bush (considering my question):
When I put my circuit together with 1 560 Ohm resistor and 1 2.6 V LED, the LED did not light up. Is this because the resistance is too high? Because I also connected another LED of the same kind, and it too did not light.





So in conclusion:
  • Is 560 Ohm too much for 3V?
  • Is 20 mA enought to ignite a firework (with 20 gauge stranded hook-up wire)
 

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If your LED is really 2.6V and if your battery is really 3.0V then the 560 ohm resistor has 0.4V across it and therefore the current is only 0.7mA. The LED should light very dimly.
With only 3V from two little AA cells, the 20 gauge wire is a dead short and will kill the battery very quickly before anything gets hot. You need many Amps of current in the 20gauge wire for it to get hot enough to ignite fireworks. A 12V lead-acid car or motorcycle battery could do it.
 
Hmm... So if I do go for the 12V, would the 560 Ohm resistors be sufficient, or would I be better off getting lower-resistance ones?
 
Led Series Resistor

Just for information for anyone on this site who may be unsure about using leds........
To safely operate any led from a given voltage you need to connect a resistor in series with your led.To calculate the resistor value(in ohms)=
R=(Vs-Vf)/If
Vs=Supply voltage
Vf=Forward Voltage drop across the led being used(1.2v,2.5v etc)
If=Forward current through the led being used(in mA=Milliamps)
for example
running a led with Vf =2.5 v,If =20mA from a supply of 12v dc=
R=(12v-2.5v)/0.02= 475 ohms
so you would use a 470 ohm resistor that being the nearest prefered value
The current of 20 mA is divided by 1000(20/1000 =0.02) as we are dealing with Ma and not Amps
this is a very useful formula for working out the correct value series resistor for any given voltage.
regards mike
 
You could use a 0.25W 10:eek:hm: resistor to ignite a firework from a 12V supply. When connected to 12V the resistor would get very hot and dissipate 14.4W causing it to get hot enough to light the fuse.

However I would strongly recommend you connect it inseries with a 3A polyfuse so it won't blow up the battery if the terminals short.
 
A 1/4W resistor dissipating 14.4W is a fast-blow fuse, isn't it?
It might even de-solder itself.
 
Don't carbon film resistors have a negitive temperature co-efficient?

When the reisitor gets to 500 degrees its resistance is likely to be much lower than 10:eek:hm:, also I'd be worried about the bonding wires short circuiting which could start a fire or even blow up the battery.
 
A resistor might well work but might not be convenient to use. I also wonder if it would impart enough heat to ignite the device.

I think a much better solution is to use very thin nichrome wire. You can get very high temps. For example, 4 inches (~10 cm) of #38 nichrome will have a resistance of 13.33 ohms (40 ohms/ft) and will pull around 900 mA at 12V. This will reach around 1600F. More than enough to ignite anything combustable. Here are the tables I used - **broken link removed**

I'm not sure what's available to you but sometimes you can get this stuff in hobby stores.

You can even make a low current continuity checker by feeding the voltage through a large enough resistor to prevent heating but still light an LED (10 mA or so). Your fire switch would be a dpdt which switches the resistor and LED out of the circuit. I'd use a momentary switch so you don't discharge the battery.
 
Aren't all your everyday mad bombers these days all using light bulbs with the glass broken off?

Bob
 
My homeland is "The Temple of the Screaming Electron".

You should come on over and take a look at this thread
**broken link removed**
 
While I am sure that this circuit would work there is no safety to it at all, as a mater of fact I would be scared to use it totally to wire my stuff as it could blow up in my face and trust me that is not a good thing. In this thread you will find that many questions are addressed. Also if you want to keep your BATF certification you have to play by certain regulations.

https://www.electro-tech-online.com/threads/electronic-firing-system-for-fireworks.21046/
 
Alright, now I know I've done something wrong. I purchased several small 12v remote batteries. I hooked one of those up in series with a 560 ohm resistor and an LED, and nothing happened. I tried it again with a brand new LED and a brand new resistor, and...nothing happened.

Here's my circuit:

------------|560 Ohm resistor|--------
| |
pos Neg
12 V LED
battery Pos
neg |
| |
---------------------------------------

I hope I'm not just extremely dense.
 
Why scribble a schematic in text? Draw the circuit properly!
The battery and the LED have polarity. If one is backwards then the LED won't light.
Make it like this:
 

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If the LED came from a grab bag, it may be invisible IR.

Bob
 
Doh! I didn't see that my ASCII circuit got screwed up.

It's a red LED, as I bought it specifically.
If I were to place the LED backwards with the resistor, would that blow it out? Also, if I were to blow out an LED, would there be some visible damage (IE way to know it's dead)?

Also, (came to me last night) should I be using a larger capacity battery? I am currently using tiny (smaller than AAA) 12V keyless remote batteries. I was wondering if I should go out and get like a 12V lantern battery.
 
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Instead of guessing about batteries, go to a manufacture's website and look at the datasheets.

Energizer's largest 12V tiny "remote" alkaline battery, the A23, is rated for only 480uA.
Your LED with the 560 ohm resistor needs 17.9mA which is 37 times higher.
I think the LED should have lighted dimly for a few seconds if the battery was brand new.
 
Yep, that figures. If I had had an ounce of sense in the store, I would have gone for the bigger battery right off the bat. And while I'm at it, I may just pick up a voltmeter. Thanks for your help.
 
Go for a lead acid battery, at least then you can recharge it when it goes flat.
 
Go out and buy a glow starter and a glow plug from your local remote controlled car hobby shop

These are hand-held, and small, and get very hot (they glow red). They last about 2mins if left on all the time, and use a 1 amp, 1.2 volt battery.

Now rip the glow starter apart, add a led and a switch.

Job done.
 
Aren't they a bit expensive for a single use device though?
 
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