Remaining power after flight query

[Simon Bee]

Flying my EDF with 6S 5000, I was shocked to see only 14% remaining after 3 1/2 mins. However after the battery cooled the remaining percentage was back up to 30%. Not sure whether I should reduce the flight time because 14% is too close for comfort.

[xviper]

No, it's not, especially if it's during or immediately after being put on load. What's important is what the voltage and % remaining is during it's "resting" stage after a flight and that can be at least a couple minutes after the plane is back at the bench and battery unplugged. I don't worry about it unless the volts/per cell at "resting" is 3.7 or below - not too concerned about % remaining either. You'd be surprised and probably shocked to see the voltage during heavy load, which can be 3.0 or less and that can happen right after take off and the jet is on it's first turn. Probably not a good thing for some pilots to have real time telemetry on EDFs. They'd spend most of their time being freaked out.

[Simon Bee]

Great, thanks that’s very interesting

[HangarQueen]

That is exactly the reason why measuring battery voltage with telemetry is so tricky and inefficient.
I use a current sensor, and my radio constantly calculates consumed mAh. As this isn't perfectly accurate either (every sensor has some error in measurement), I do my own calibration by measuring how much mAh my charger puts back in afterwards. I then have the radio call out consumption every 500 mAh. I use a timer as a backup, in case my telemetry fails for some reason.
If you use voltage sensors, you will hear the voltage sagging whenever you open the throttle. Even though voltage is the best indicator for remaining capacity, the problem with it is that it is only useful when the battery is at rest, no load. That is a situation that is not so common when in flight. You would have to land and wait a minute or so before you can actually measure the voltage at rest. Not so useful.

[Simon Bee]

👍👍Thanks

[xviper]

That is exactly the reason why measuring battery voltage with telemetry is so tricky and inefficient.
I use a current sensor, and my radio constantly calculates consumed mAh. As this isn't perfectly accurate either (every sensor has some error in measurement), I do my own calibration by measuring how much mAh my charger puts back in afterwards. I then have the radio call out consumption every 500 mAh. I use a timer as a backup, in case my telemetry fails for some reason.
If you use voltage sensors, you will hear the voltage sagging whenever you open the throttle. Even though voltage is the best indicator for remaining capacity, the problem with it is that it is only useful when the battery is at rest, no load. That is a situation that is not so common when in flight. You would have to land and wait a minute or so before you can actually measure the voltage at rest. Not so useful.

It would appear that you understand this whole concept of "real time" LiPo voltage and MAH status. There are many who don't and think that even the most accurate telemetry information is all anyone needs. "Real time" read outs of LiPo condition is by no means what the battery will be once the flight is over and the battery has a couple of minutes to come to rest. A battery can show a real time voltage of 3.0v/cell (or less) under heavy load and yet still not trip the LVC on the ESC. Even mah used (or remaining) has to be taken with a grain of salt. I've had telemetry tell me that at the end of a flight, my battery has used up 4000mah when it's only a 3000 mah battery. Imagine that! Only by repeated "trial and error" and the use of the timer and battery checker after a flight, can we even remotely gauge how we fly a plane and for how long while keeping the battery safe. IE, check battery before flight, go fly and keep track of how you fly, be conservative with the timer, land, unplug, rest, check battery, adjust timer for next flight, repeat.

[HangarQueen]

Yeah, like I said, even with current sensors you need to do some sort of calibration. I take notes for each models at which telemetry-calculated consumption that I need to land.
I once did an experiment to use a LUA script to calculate internal resistance of my battery at takeoff, by first measuring the no-load voltage and then using the voltage drop at the measured current, but it proved too unreliable, because the throttle values aren't always the same for each takeoff, different dynamic etc.
I've been flying like this for years, and honestly can't understand that people still want to use only timers when all this technology is there and readily available. And really not that hard to use.
I do use battery voltage measurement though, but only to detect cell voltage differences, which then trigger aural alarms on my radio when the difference exceeds the threshold.
I remember a Youtube video of a guy that was promoting the then new Eflite F16, and he was so enthusiastic about the new battery voltage telemetry....he crashed the model at the end of the video when the ESC went into LVC 🤣

[xviper]

I guess some of that Spektrum "smart" stuff isn't that smart.

[HangarQueen]

It is smart marketing for sure 🙂

[xviper]

Horizon is king of marketing and building up hype on new models.

[SanExup]

This is highly informative, thanks!