On Sat, 26 Feb 2011 01:57:57 -0700 Bdale Garbee <[email protected]> wrote:
> The first is that because we're putting a very low resistance across > the LiPo when firing a pyro channel, and LiPo batteries have a very > low source impedance, there's a *lot* of current flowing. As long as > your match actually fires and goes open in something like 150ms, you > should be ok, but if somehow the match retains continuity, you're > going to drain a lot of energy out of the battery and warm up some > traces in 2 seconds. > > The second is that there's a risk of pulling the 3.3 volt rail down > far enough to cause a processor reset if you keep the FET "on" with a > low resistance across the pyro terminals for long enough. I put a > 100uF ballast capacitor on the 3.3V rail which is on "the other side > of the regulator" from the LiPo to help protect against this > eventuality, and again, as long as your matches actually go open in a > couple hundred milliseconds, all should be fine. But if you have a > short across the pyro terminals and leave the FET on for 2 seconds, > you should expect the processor to reset leaving you in a pretty > seriously undefined state! I had considered both actually. When issuing i DoIt drouge, the prompt returns in about 2 seconds as expected. A subsequent t shows that the ematch still has continutity so it's drawing current throughout the 2 seconds and it doesn't open up. The processor didn't reset but I really don't want to risk it in flight. I'll try backing off on the value to see where the ignition point is at and then add a safety margin of 50% or so. Further ground testing might show that the deployment charge opens the ematch but for now I'm going to assume it remains conductive. I'm curious about the Q2G2 igniter - what is the resistance of the device? I've seen reports of 3 ohms but I'd like verification if you could. -- ~Don ------------ _______________________________________________ altusmetrum mailing list [email protected] http://lists.gag.com/mailman/listinfo/altusmetrum
