- #36
minorwork
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I agree with everything you've said. Seems a waste to haul weight of the batteries if after they've ignited they have any capacity left. I think a properly sized capacitor would be lighter. But, yeah, you got a bit of figuring and/or grunt work testing to determine if one of those 4700mfd's would do the job. The coin cells. I wonder if they would weigh more than the capacitor? The 35 volt cap should not breakdown at 28 volts. That is what the DC power supply sourced for the carbon monoxide detection system I am familiar with.negitron said:IF the igniters fire before opening, then series would be better for those reasons. I'm not familiar enough with the ones the OP is trying to use to state that's definitely the case, however. Perhaps an experiment is in order.
The problem with series is that, as described above, you require 9.6 volts per igniter--really, you need a specific current to ignite them, but if you need 9.6 volts to provide that current for one igniter, then for 3, you'll need 28.8 volts. The problem here is that 30 volts worth of batteries is heavy; not something you want in a rocket where mass is absolutely critical. It wouldn't be a problem for a ground-based system, since you can hook up as many batteries as you need. But in a rocket, you need to minimize the mass of the infrastructure so you can maximize the payload.
Now, one thing you can do is something akin to what happens in a camera flash you mentioned earlier. The 1.5 volts DC from the battery is converted into a high-frequency AC, which is then kicked up to a higher voltage with inductors, converted back to DC and stored on a high-voltage capacitor. But, this is probably needlessly complex and beyond the OP's capabilities (no insult to him intended). I say if due care is used in making the connections and each igniter is tested individually prior to installation, parallel is the way to go. You can store your 9.6 volts from a set of lightweight Li cells (I suggest coin cells, since they're small footprint and this will essentially be a single-use application) on a high-density cap, as you suggest, and discharge it through the igniters; this should work fine, assuming that the quality-control in manufacturing the igniters is good enough to ensure they're all within a few percent of each other for resistance.
I did some shot firing in the mine too. Some. We wanted to get home early so we set off a few (quite a few) more than the 20 at one time. We went into overtime putting back up the ventilation stoppings and doors we blew down.