Does the power module know how many cells are used in the current battery?

[NullVoxPopuli]

Maybe this would be really complicated for multiple battery setups, but I'm wondering if the APM (or maybe even pixhawk (but I don't have a pixhawk)) can know about the cells in a battery, allowing for the calculation of % left of a battery, and then send buzzer or LED signals based on that %.

[iskess]

This would require hardware that can sense each cell's voltage.
I thought about hacking one of those $5 Lipo battery alarms that allow you to set the alarm voltage point. When the alarm sounds, the voltage going to the speaker would trigger a Mavlink message to the GCS.
I think this would be the easiest way, requiring a minimum of coding.

[NullVoxPopuli]

Hmm. Currently, the APM just knows current total voltage, yeah?

[SkyHawkDP]

If you just want to calculate a more acurate % left, I wonder if it would be neccesary to have access at cell level. Most of us charge with balance charges, so we should know if our battery has a bad cell (and therefore not use it). But we can know which batteries we have, by using a few of the basic parameter settings.

Our Failsafe trip voltage should tell us which battery we are using. 2S, 3S, 4S etc. All batteries are not alike and the curves differ. Also they sag when first loaded. But if you wait for something like a minute of typical load, and then measure the voltage you can calculate a close % drain. If you want to have a time estimate, further measurement of the slope of the curve, should lend some knowledge about that.

[iskess]

I had a crash shortly after takeoff on a fully balanced battery when one cell failed. Early warning would have given me the time to get on the ground safely.
That is why this post grabbed my attention.

[Felixrising]

If your voltage divider is a known quantity and you know your max cell
voltage (ie 4.2v or 4.3v per cell to play it safe) then you can calculate
your cell count

https://github.com/multiwii/baseflight/blob/master/src/sensors.c#L158

On 21 May 2014 08:42, iskess notifications@github.com wrote:

I had a crash shortly after takeoff on a fully balanced battery when one
cell failed. Early warning would have given me the time to get on the
ground safely.
That is why this post grabbed my attention.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/1093#issuecomment-43692831
.

Regards,

Matt.

[SkyHawkDP]

@iskess
The cell had to be marginal. In any case, an algorithm similar to that which I mention would probably still catch it. You'd go from "full Charged" to Fully Discharged quite quickly. The software would be indicating a quickly changing % remaining. You of course would have Mission Planner connected, or similar and could hear the % advances.

If not, perhaps a special beep alarm could be generated when the voltage is moving "quickly".and getting close to VMin.

I think a method that is monitoring all cell voltages would have to be better, but we could go crazy trying to load more weight and complexity, when it might not necesary.

[NullVoxPopuli]

@Felixrising thanks for that link to the multiwii code. That's how I thought I'd have to measure voltage without specific cell-detecting hardware. I'll be playing around with battery monitoring in the next couple days, and see what I can come up with.

[rmackay9]

This seems like more a question than an enhancement request so I'll close it if that's ok. It can possibly be reworded into an enhancement request but for now at least I'll close it.

[NullVoxPopuli]

@rmackay9 what's the best way to post more developer-oriented questions? is there a dev-ardupilot irc?

[rmackay9]

NullVoxPopuili, the drones-discuss@googlegroups.com email list is a good place.