Lithium Ion Batteries and Igniters/E-Matches

I recently lost the rev3 of my GPS tracker (link and link) and am working on doing design work for the rev4.

As a part of this rebuild, I am working on integrating the main battery into the pcb, and am considering integrating a pyro battery. However, that means I need to have the chargers onboard, and I would like to keep things such that it can charge from USB, which means that I only have 5 volts to run my chargers from.

That poses a problem, since almost all of the pyro system I have seen use at least 7v, usually 9 or 12v. I am talking about using 3.5v...

The thing is that if one looks at the spec sheets for an ematch (m-tek for example) the resistance of the ematch is 1ohm, the resistance of my battery is .025ohm. and my switch .005ohm. The recommended firing current is 1a. Using a 3.5v battery that leaves over 2ohms of extra resistance for wiring, switches, etc, and it seems like all should be happy...

So why do people insist on using such high voltages for altimeters?

A Li-ion battery will fire e-matches just fine. I haven't checked the specs of the battery, but voltage is unimportant as long as the current is adaquate. I've fired matches with a 1.5V AAA cell. Make sure you isolate the altimeter circuit from the brownout during pyro firing - MOSFET switch and cap or separate battery.

I don't know why most altimeters require such high voltage. The ones I've looked at regulate the battery to 5V for the electronics and use full battery voltage on the firing circuit.

Being relatively new to this, and since I make my own altimeters, the only way I have ever fired deployment charges is via a single Li-poly cell. You'll need to make sure that the cell you use doesn't have cell protection circuitry that could mistake the firing current for a short. Ground test and be careful charging!

Very good news

I see a pretty awesome tracker in the works...

intial drawing of where some of the stuff is going to be going (those are chip antennas on the ends of the board)