New Altimiter StrattologgerCF?

The StratoLogger CF will actually operate as designed on down to about 3.6 volts, and with slightly reduced accuracy down to about 3.2 volts.

A fully charged single LiPo cell is about 4.2 volts, so that is fine. Since the current draw of the SLCF is so low, it is unlikely that the battery voltage would ever fall below 4 volts during your flight.


The only thing you have to be concerned about is this:

If you have a LiPo cell that can't put out a lot of current, its terminal voltage will drop when the ematch firing current is pulled. If the voltage drops below 3.2 at that point, you could encounter difficulties.

The brownout protection built into the altimeter is designed to provide 2 seconds of backup power with a 9V battery, more than enough for the altimeter to ride through the 1 second firing period even if your ematch is shorted and kills the battery voltage altogether.

But with a lower voltage battery, you will get a shorter brownout protection period. As long as your battery can keep its voltage up above 3.2 volts while your ematch is firing, this will not be a problem at all. Also, if the battery voltage does drop lower, but for a short duration (i.e. you are using a proper Oxral/Daveyfire/Jtek commercial ematch that fires and open-circuits in about 1/1000 of a second), there is no problem.

The only time you could run into problems is if you have a weak battery, an ematch substitute that draws a lot of current, and draws it for the entire 1 second firing period. Then the brownout protection voltage could drop below 3.2 volts, and the altimeter would reset.

If you are using one of the above mentioned commercial fast-reacting ematches, and your battery can supply at least 1 amp, then there is no problem.

If you are using something else, then you should do a ground test, pulling a vacuum on the altimeter with the battery and ematch in question connected, and download and look at the voltage graph after the test. If the ematch burns quickly, and the voltage only drops briefly (or if the voltage never drops below 3.2) then you are all set.

Also bear in mind that some LiPos can produce a very large amount of current into a short circuit. If you accidentally short the output on the StratoLoggerCF, then this current could damage the altimeter. The altimeter employs current limiting to reduce the likelihood of damage, but if a very large initial pulse of current is put through the altimeter before current limiting takes place, damage to the altimeter could occur.

You can look at the downloaded graph to get an approximation of the peak current through the ematch (PID & PIM). Ideally you'd like these to be less that 5 or 6 amps. 10 amps is OK if for a very short time (less than 50ms, or one sample period on the data)

Also, to dispel a common misconception, a LiPo can put out a lot more current than the mah rating multipled by the "xxC" rating. The "xxC" rating multiplied by the mah rating gives you the maximum continuous current that the battery can supply without damage to the battery, but the battery can supply a lot more current in a short burst.

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