Battery Failsafe Operates despite Battery Good

10 or more test flights yields same result, quad flies for a moment or two then Bat Failsafe operates even though Battery is actually well above critical level set. Have swapped out (3DR type) power supply unit, props and different batteries, always with the same result. Was getting more flight time with battery fully charged before onset of failsafe.
Log from flight before screenshot shows similar events
2019-11-23 13-05-48.bin (682.0 KB)

Any ideas on what is wrong would be appreciated. thanks Bruce

The log you posted has the battery failsafe set at 14v and the FS-Batt operated after some time at less than 14v.

It’s doing exactly what you set.

You are not logging Amps but have a battery capacity set in your battery monitor.
Remove the capacity or setup you’re Amp readings.

This problem does exist. If you turn off or ignore the battery runaway protection function?

If you do not set EVERTHING up properly you cannot expect the flight controller to behave properly.

So, the reason you are having problems is not do to a hardware failure. The problem is the result of human error

Do as MBOLAND said. Install a battery monitor, calibrate for voltage AND current and then you can setup the battery failsafe.

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Thanks Mike, I do realise that the failsafe is set at 14v but I am surprised that the voltage on a battery reading 15.5v at arming drops to below 14v so soon into flight. I knew that there would be voltage drop in flight but not that much. That seems to be what has caught me out. I have flown this Quad successfully many times before but only just decided to set battery failsafe. I am usually flying out to sea about 300m and I want to make sure that the Quad will return if I haven’t realised that the battery is getting too low.

I have now set the monitor to Voltage and current as suggested by OldGazer.

So given my setup, LiPo battery 3200mAH 4s normally fully charged at around 16.3v, what would you recommend that I set the battery failsafe voltage at.? I was getting about 20 mins flying time in 4 to 5 minute flights before I mucked around with the battery failsafe.

cheers, Bruce

Also spend some time calibrating the voltage sensor at the lowest expected voltage, they can be a bit non linear. It almost doesn’t matter how accurate the voltage reading is at 16 volts if the battery is going to sag to 14v

That battery was only at 15.3v when you started so it was not a fully charged battery at takeoff.

A good example of the voltage would be the Solo which uses 4S and has a default of 14v BattFS.
Thats fine for nice new batteries but with older batteries you only get 3 to 5 minutes flights just as you are experiencing.
I have readjusted the FS to 13.2 (3.3v/cell) as the older batteries will still give the current but at lower voltages. We have even tested them down to 12v but that is REALLY hard on the batteries, don’t expect a long life from them if you do that a lot, but there was still enough current to keep flying even longer.

Battery oneOone: 4.2v is fully charged, 3v is fully flat, that gives you 1.2v of operational voltage which you do not want to exceed 80% of this capacity, so that gives you an ‘on the ground’ voltage of 3.2v.
Your point of failsafe for return is function of the type of flying, so long journeys over water you want to be heading home at 50%.
Close flying not so much.
It’s very much a user choice about you circumstances.

Thanks Mike, yes I did know that the battery v was at 15.3 when I did that test flight. I have only just bought it so I wasn’t expecting a quick v drop.
Thanks for your suggestions I will reset at around 13.5 v and see how that goes.
cheers Bruce

Make sure you adjust the BATT_VOLT_MULT parameter so that the battery voltage reading in the ground station matches the voltage of the battery as noted with your multimeter and/or FLVSS sensor.