Battery flight time off on one of my APM quads.
I have two quads one is a Walkera x350 pro that I changed the flight controller to mini apm. The other is an F330 that is running APM 2.6. Both have telemetry and feed data to my android tablet when flying. I have three battery’s that are 5200 MA that were part of the x350 pro. What is strange is I get much more mAH out of the batter with my x350 pro than with my f330. Here are the flight stats.
F330
Flight time= 14:30
Average AMP draw= 13 or so
LVC(under load)= 10.5 (this is when I landed)
Landed volts=11.4 (after five min rest)
mAH used=3120
mAH put back in during charge=3382
Battery resistance 23 mo
So you can see I am not getting to the 20% capacity before hitting 10.5. This could be normal if my other APM power quad did the same but it will use mAH 4138 before hitting 10.5 and it is much heavier and therefore for draws more amps. Around 18 to 20 amps in flight on the same battery.
I did compare the power blocks voltage reading to my multimeter on a full battery and adjust it a bit before this flight. Can any of you tell me if I am missing something?
I think you were almost there if you carried on with analyzing.
i you are using the same under load voltage foe both, the higher current drwa setup will naturally hit voltage limit first…you listed battery resistance 
The 7Amp or so current draw difference equates to an increased volt drop of about 161mV
Would be interesting to include this offset one way or other and see if the two setups end up with the same AH drawn in practice.
I didn’t explain the situation great but the quad with the heaver current draw is getting the same flight time as the one with the lower draw. It seems to be that on the lighter quad the under load volts are low in comparison. I am thinking it is one of two things.
1: Power block is not accurate under load.
2: Tempter difference. The heaver quads battery is completely enclosed on the x350 pro. The f330 is an open frame quad. After flying both over the winter I know I get 30% to 40% less flight time from both depending on the tempter. As it has been worming up my flight times are increasing quite a bit. I wonder if the enclosed frame of the x350 is keeping the battery wormer and therefore giving better output. I flew the f330 at 7 degrees census for 14 min and at 21 degrees census it flew 18 min. I did not fly the x350.
I suppose I will have to fly them both on a worm day 20 degrees + where the open vs closed frame will not be a factor.
ah sorry, yes I realised I made a mistake looking on my lunch (can’t reply from work)
personally I tend to go on Ah used rather than volts, and set the volt alarm a bit lower to catch a dodgy battery, but not too low that you don’t have any time to get it back. But saying that none of my flying is very far from me.
yeah it is backwards to what I thought originally,
How easy is it to remove the power module from one of them? If they are connectorised on input and output still, they can be put in series on the bench, the one on the bench will read slightly higher voltage under heavy load, but it will allow comparison at the same time with same current.
Thanks RabbitStu for the suggestion of swapping the power block. I don’t think I will bother swapping but will just order another one as they are quite cheep. I would like to go by the MA only but temp can greatly reduce that. I am going to test both on the same day when the temp is above 20c as I thank temp is causing my results to be to hard to interpret.
So the problem is definitely the power blocks readings under load. I put one of those lipo monitor/buzzers on the balance plug of my battery. I set it to go off at 3.5 volt per cell. The telemetry reading on my tablet hit 10.2 before the buzzer went off. The battery is now resting at 11.2 after 10 minutes of rest. So for whatever reason the when not under load the lipo monitor and telemetry agree but when under load not so much.
cool, glad you found it. Sounds like the one that reads lower has more series resistance somewhere between the battery and v sense.