Which voltage indicator to trust?

[WVU_Scott]

Hi All—new member and new Phantom 2 owner here!

I just did my first flights with a Phantom 2 Pro Package from Aerial Media Pros (Zenmuse 3D gimbal, GoPro, Futaba 14SG Tx, iOSD). So far the system is working beautifully and I've been happy with it.

Aerial Media Pros recommends always landing when main battery voltage reads 11.1V. This is fine, but I noticed a couple things while flying yesterday: First, the voltage on my video monitor (from the iOSD) doesn't match the telemetry voltage displayed on the Futaba—it was typically at least .2 apart. For example the Tx indicator would say 11.2V while iOSD said 11.4V. Any idea which one is more accurate? Or should I just be safe and always use the lower-reading one?

I'm not opposed to being conservative---but at the same time I want to get the most out of each battery while still preserving a reasonable safety margin.

The other thing I noticed is that voltage indicators always jumped up after landing. This is obviously because motors draw a lot more power...but again, I just want to be sure *which* voltage indication to use---the in-flight voltage? Or on-the-ground voltage?

My point is that all voltage measurements were a bit "sloppy" and tended to oscillate up and down a bit.

Any advice is appreciated!
Scott

 

[N017RW]

There is always measurement uncertainty and when flying (i.e. under load) the battery drain is dynamic. Seeing slightly different readings from different hobby grade systems does not seem out of the question.

The P2s' 'smart battery' cutoff can be set in your MC firmware but it is based on % remaining not volts. DJI explains they have some type of algorithm to determine this based on various factors.

The general rules of thumb with LiPos has been never discharge below 20% of capacity. This is mostly consistent with DJI's default settings/philosophy as well.

As far as voltages go at time of landing... 11.1 under load is a bit conservative.

Typically 3.2/cell is considered the accepted cut-off under load and 3.7/cell at rest.

Read more and then make up your own mind but for now the P2's default battery monitoring features and parameters will protect your LiPo 'investment'.