Replies to This Discussion

Permalink Reply by Farooq Niaz on October 24, 2011 at 10:12am

Hi

 

Faced the same issue and I changed the value of the Voltage Divide Ratio (Rescaled it).

//#define VOLT_DIV_RATIO 12.6
#define VOLT_DIV_RATIO 14.364  //scaling 1.14 times

# define BATTERY_EVENT    ENABLED

# define LOW_VOLTAGE            10.5

# define CURR_AMP_PER_VOLT        27.32

I am using AttoPilot voltage and current sensor. Now I am approximately measuring the exact values

 

 

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Permalink Reply by Kirill on October 24, 2011 at 12:43pm

I am using AttoPIlot sensor. Had to rescale the voltage divider ratio to get the right values too.

The difference in measurements may be explained as a voltage drop, because when you define voltage using multimeter - it doesn't cause big current flow (and a voltage drop as a consequence).

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DeveloperPermalink Reply by Michael Oborne on October 24, 2011 at 4:39pm

the voltage monitor screen only works on the yet unreleased version of APM

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Permalink Reply by apocolipse on November 5, 2011 at 2:11pm

Hey guys, i've been using the latest trunk as Michael said for the advanced input stuff in MissionPlanner, with the attopilot voltage/current sensor

 

Couple questions, first, i'm not using a voltage divider on my APM, just using the attopilots, i'm having to set my voltage divider ratio to 17.44 to get accurate reading on a 3s battery!

I have a feeling thats too high and maybe APM isnt handling the sensor correctly?

Also from the data sheet, the amps-per-volt that is set default in the APM code seems wrong too

50V/180A  =  63.69mV / Volt     18.30mV / Amp

50V/90A    =  63.69mV / Volt     36.60mV / Amp

13.6V/45A =  242.3mV / Volt     73.20mV / Amp 

for the 50v/90a sensor that would be 36.60mV/Amp, but APM default is 27.32? really confused as to why.   Which part of code is responsible for directly reading those pins?  I'm wondering if maybe the code could be better handled for that setup, imo case should simply be for battery monitor option 4 (using the volt/current sensor externally) expect no volt divider resistor on APM side, and in Mission Planner have the user input volts/volt and volts/amp, instead of voltage divider value (its confusing and misleading with this setup, and leads to unnecessarily arbitrary values)

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Permalink Reply by apocolipse on November 5, 2011 at 2:14pm

Ahh i see the 27.32 is the inverse of .0366V/1A, however the 17.44 volt ratio i'm having to input to get correct voltage reading is still bothering me

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Permalink Reply by apocolipse on November 5, 2011 at 5:30pm

I think i've found another issue in that the Attopilot sensor is made for 3.3v ADC and the ardupilot code references 5v (actually 4.68v in code) ADC, does that matter at all?  I'm not overly versed in arduino and/or analog inputs but that seems to be a discrepancy

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