Documentation the way it ought to be.
This all started when we tried to find some scientific data that we could believe in that compared different LiPo batteries and their likely performance when flying a Cinestar 8. We searched. We googled. We verbed our nouns. But to no avail.
All we could find were reports with a slight whiff of a kindergarten science class mixed with a dash of gossip. A typical one would say something like: "Using a Fribnitz 405 battery on a Thursday, with a Mumblecopter with 6 1/2 motors, a Canon 5D Mark II and flying like banshee when it was windy, I got oh, meh, well a good few minutes out of the battery."
Not quite the scientific repeatable test, we had in mind...
So we sat and thought for a while. We wondered what would happen if you put a really large resistor across the terminals of a LiPo battery and pulled 60 Amps out of the battery to simulate the behavior of a copter in flight and then made a note of the voltage, the current, and the temperature of the battery? What could possibly be the harm in that, eh? Could anything possibly spontaneously ignite? No. We knew you'd agree.
A little bit of red wine and mathematics later, assisted with some Ohm's Law, we figured out that we could construct an industrial sized dummy load that would allow us to do just this. Initially for 4S batteries, and after that, with some more of these honking great resistors, for 6S. So that's what we did. Kids: Do not do this at home; go over to a friend's house. We're sure her parents won't mind -- and the place is probably insured.
We then used a computerized set of sensors to monitor how the battery voltage, current and temperature behaved until the battery dropped from fully charged (for 4S that's 16.8 volts) down to the point where any right-minded copter pilot would probably want to be landing the copter before the copter decided for itself that it would be landing (for 4S, 14.0 volts).
Then we tested several different LiPo batteries, both individually and in pairs just to see what happened when we halved the load on each battery. And the results are what we describe in our report.
Caveat: Right now this document suffers from a lack of testing batteries from different vendors, and the lack of repeated testing of the same batteries that we already happen to have, but we'll change that as we get more time and more batteries.
The current version of the report is available without charge. (Yup. It's the world's first totally awful LiPo joke).
It's called A Rather Good Guide® for Comparing Certain Lipo Batteries and, yup, just click on the link above.
For the geeks, 4 x 0.5 ohms, 1,000 watts.
For the non-geeks: four honking big resistors.
Copyright © 2015 Johnson-Laird Inc.