Best Practices using LiPO Batteries
If you're constrained by space and/or overall payload weight for your project, you've likely considered the use of a smaller, lighter battery technology like LiPO batteries. While the RRC2 and RRC3 altimeter designs were originally targeted for use with conventional off-the-shelf 9V alkaline batteries, they will also work with LiPO batteries.
There are a few "Best Practice" considerations and guidelines to follow should you decide to make the commitment to integrating LiPO into your system design that we'll layout here. If you follow these recommendations you'll have the highest degree of success when making this choice for your project.
Choosing the Ideal Battery
First, the notion of "Ideal" is a relative term, and our intent here is to provide the most relevant trade choices so you can consider what works best for your specific project.
2S vs. 1S
The RRC2 and RRC3 are 9V alkaline "optimized", which simply means that the higher the battery voltage provided by a 9V alkaline battery provides longer brownout protection to keep the altimeter afloat should there be a temporary glitch or interruption from the battery system. With regard to LiPO battery voltage, the 2S battery is the preferred choice since it provides a nominal 7.4V level over a 3.7V single-cell 1S battery type. However, if one employs 100% solid, no-bobble interconnection wiring practices (batteries, switches, deployment charges) then the requirement for brownout protection is greatly diminished making this trade less significant.
Our choice for the best LiPO when using the RRC2/RRC3 is pictured above (the
"Blade" from Horizon Hobby). This battery provides similar performance to that of a top-shelf 6-cell 9V (5A) alkaline with its 15C rating.
(320 mAh x 15) / 1000 = 4.8 amps
Prepping your flight when using LiPO Batteries
Because LiPO batteries are capable of supplying massive amounts of current, there are collection of caveats to adhere to when designing and prepping your project for flight readiness.
- ALWAYS pre-measure your electric match resistance
This precaution is a best practice recommendation regardless of battery chemistry, and it's even more important when using LiPO's. Measure each electric match you intend to use with a DMM (Digital Multimeter) to ensure it has a NOMINAL RESISTANCE and it is NOT SHORTED. This resistance will vary slightly by supplier or brand, but in general a nominal resistance of about 1Ω is what you're looking for. - NEVER wire redundant matches in PARALLEL to a SINGLE EVENT
If you want to use redundant electric matches for each deployment charge, always connect them in SERIES (just like the pyro guys wire up redundant matches). This ensures the resistive load on the deployment event electronics maintain a nominal resistance and don't dip down toward the region of a dead short.
- AVOID the use of METALLICS with deployment charges
Because this can be a potential path for shorts during the activation of a recovery event, it's also best practice minimize anything metallic that could potentially be exposed to the "chip end" of the electric match.
