I am creating a fireworks launch controller using an Arduino Mega. I plan to connect them to an 8 bit shift register then to a MOSFET so I can increase the voltage to the igniter. I will be using Talon igniter clips (PyroUniverse.com is for sale | HugeDomains). I understand how each component works but I am struggling with the math to decide which components to use. I plan to use (2) 9v batteries in series as the power source for the collector and an IRF540N. I've been told that this will work but I would like to understand the math to prove it. My biggest concern is the amperage that will be applied form the 2 9v's, I am afraid it will burn them up to fast.
Yes you will burn them up, in fact I would be supprised if you could get one ignition from them.
You need something like a small lead acid accumulator.
As for the maths, you need to know the resistance of the igniter, then work out the current with ohms law. These sort of things take about 5 Amps or so at 12 V but only for a fraction of a second.
Well, the "clips" specified in that article were measured at between 7 and 16 ohms, so you need at least 1.2 Amps - at 12V.
Judging by the comments, you do not need 18V from two 9V batteries in series. Big question is - just what sort of 9V battery did you have in mind - surely not a little "PP3" - that would be absolutely useless unless you used half a dozen alkaline in parallel. A pack of six alkaline AA cells would probably suffice, but better to use eight for 12V in this case. A 12V "Gel Cell" (lead acid) rated at least 4 AHr would be a better choice overall (and is rechargeable). Or ten NiMh.
And further complications if you plan to use igniters in parallel, though since they fuse, what you can actually do is to fire them in rapid sequence at 200 mS intervals, leaving each switched on for 400 mS.
I'm very happy to work through the math of this, but we need to establish:
- how many igniters you want to operate simultaneously;
- how many igniters you want to switch in rapide succession, (say, with less than 500ms between firing); and
- precisely which 9V battery types you plan to use.
12V SLA or 11.1V LiPo are options for high current supply (20A
without strain - handle 10 simultaneous firings)
However having enough capacitance would reduce the peak current
demand from any batteries. Something like 47,000uF would be needed
per simultaneous firing, then a weaker battery would be needed.