Originally Posted by jrjr
I know that Lipo's are not supposed to be run below 3v/cell. How do you know when that point has been reached and you should land the plane? Other than landing and measuring, is there something in, maybe the ESC, or in the Lipo itself that does that? If it shuts the battery completely off that would be bad since you would have no control.....
Actually, the critical number is the resting cell voltage that should not be below, the nominal voltage of lithium polymer cells, 3.7V. All serious RC modelers use a count down timer either the built in one in your transmitter, or a separate one with the alarm set at the known time when one should land. This is determined by experimentation because there are many variables that affect the discharge characteristics of any model including individual flying style. You should initially start with your time very conservative around 4 minutes. When the alarm sounds, land, then remove the pack and then check the voltage of the pack/ cells. Next flight, add another 30 seconds or so, and so on until you have found the optimum flight duration. so basically, once you land, your pack voltage shouldn't be lower than 7.4 for 2S, 11.1 for 3S, and 14.8 for 4S and so on. Actually, I limit my flight times a bit conservatively for a bit pad in case my flight consumes a little more than anticipated. I limit my flight duration that corresponds with a resting cell voltage around 3.80-3.85V.
These work very well, inexpensive also, I use these with my transmitters that don't have a built in timer: