Fuel Cell - Hydrogen Tank Pressure in Percent

coaxftw · February 15, 2023, 8:58am

Hello!

According to Intelligent Energy Fuel Cell 2.4kW — Copter documentation, I set [BATT2_MONITOR] to 18 for the hydrogen tank telemetry. Recommended is also to set [BATT2_CAPACITY] = 100 in order to “give a sensible readout of a percentage on the GCS.”

Here is my question: Since the fuel cell only reports the tank pressure in bar, what it considered 100% fuel level? Is my understanding correct that if I set [BATT2_CAPACITY] to 100, the calculations always consider a full tank on every startup? However this seems not to be the case, as I get 30% now reported from the autopilot on startup.

grafik

What is “100%”?

Thanks in advance!

iampete · February 15, 2023, 9:40am

Code is here:

github.com

ArduPilot/ardupilot/blob/fe9461242e06aa8f74328ff1c7931990f5cd0687/libraries/AP_Generator/AP_Generator_IE_2400.cpp#L46-L49


      
          // Scale tank pressure linearly to a percentage.
          // Min = 5 bar, max = 300 bar, PRESS_GRAD = 1/295.
          const float PRESS_GRAD = 0.003389830508f;
          _fuel_remain_pct = constrain_float((_parsed.tank_bar-5)*PRESS_GRAD,0,1);

100% is 300 bar.

coaxftw · February 15, 2023, 10:39am

Perfect answer, thanks a lot!
Now I just need to check how I can change the gradient.

coaxftw · February 15, 2023, 11:03am

Changing the code seems to be more complicated than I thought.
Could you point me in the right direction? Are the steps stated in Downloading the Code / Using Git — Dev documentation needed? I thought using NP++ to change one line would be sufficient…

Any help is much appreciated.

amilcarlucas · February 16, 2023, 4:26am

No, changing one line is not sufficient. You need to compile and upload the code. And to do that you do need to follow those instructions, yes.