I buy procell Duracell 9v batteries like we use in medical equipment. I have never hand one fail.
Awesome, today I learned a cheap lesson instead of an expensive one later.
I use perfectflite altimeters. HiAlt45, SL100 and CF. They all seem to read about 0.1V less then my DMM reads, which is why I let them get below 9V as read by the altimeter before replacing. Most read 9.2V the first flight or two and 9.1 the rest of the season. They are usually at 9.1 or 9.0 the next year.I have a threshold of 9.1 volts. But what altimeters and e-matches are you using? I don't think any of my batteries read even 9 volts after a single flight with dual deploy. Maybe they sit longer on the pad and I'm slower to recover? But I can't imagine using the same battery for more than one dual-deploy flight.
If it works for you, that's great, you've got more intestinal fortitude than I do.
An important point about AA's vs. 9 volts: AA's have about 2000mAh capacity vs. 450-500mAh for 9 volts. So a AA has far more capacity to set off e-matches that can be fired by low voltage. And don't forget that battery chemistry allows them to regain voltage levels that read high but drop quickly under load, so if not tested under load they can give a false sense of confidence.
Finally, a check of prices of Duracell 9 volt (only ones I've ever used) shows just under $2 each at Costco, but a whopping $3.50 in a blister pack at Walmart. I won't by batteries over the internet - read some of the reviews in this example:
https://www.amazon.com/Duracell-Coppertop-9V-Size-Pack/dp/B0074M2J88/ref=sr_1_4_a_it?ie=UTF8&qid=1461280143&sr=8-4&keywords=duracell+9+volt
Batteries are like the motors, if it fails the results are rarely good.
Tony
Actually the amount of current going through the ematch has little or nothing to do with the battery capacity. It is a function of the match resistance, battery voltage and internal battery resistance. Not considering the battery resistance for now, a 9V battery would try to send 7.5 amps through a 1.2 ohm ematch. The 1.5 V AA would try to send 1.25 amp through the same 1.2 ohm ematch. Add internal battery resistance and those values get lower.
Indeed, a good point. I remember 1st seeing that technique used back in the 90s with Adept's 1st rev of their Altimeter utilising a cap to provide a spike of current to complement the very high impedance 12V A23 (or whatever the code is for those little things you use in your garage door remote).A battery's ability to source current can be offset by capacitor based pyro circuits though... I use them to avoid brown outs mainly, but I like them for that added safety. A completely secondary pyro ignition battery source would work as well though, particularly with how cheap some of these lipo packs are these days...
I think you misunderstood my post as that's exactly my point - the AA doesn't send as much amperage through the e-match to fire it and has a far bigger supply. When I talk about capacity in this instance I mean the number of matches I can fire with a single battery. It was in reference to a post about being able to fire a lot of matches with just a 1.5 volt battery....Actually the amount of current going through the ematch has little or nothing to do with the battery capacity. It is a function of the match resistance, battery voltage and internal battery resistance. Not considering the battery resistance for now, a 9V battery would try to send 7.5 amps through a 1.2 ohm ematch. The 1.5 V AA would try to send 1.25 amp through the same 1.2 ohm ematch. Add internal battery resistance and those values get lower....
Used once:
DVM 10mA Load
Battery #1 9.0 v 8.8 v
Battery #2 9.0 v 8.7 v
Unused, same batch
DVM 10mA Load
Battery #3 9.6 v 9.4 v
Battery #4 9.6 v 9.4 v
I've been flying for over 15 years and still have my very first altimeter, an RDAS Compact. I now have over a dozen altimeters including 3 Perfectflite CF's. Obviously the newer units have far less battery drain than the older units.
Dave,The RDAS Compact was notorious for its high current requirements (70mA to 90mA) which were higher than pretty much every other altimeter by quite a bit. For comparison, the AltAcc needs less than 5mA.
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