Can somebody confirm this for me? I am using a 6s Lipo (25.2 volts Max when fully charged) to provide power for my motor. I want to monitor the battery voltage with the GCS, attaching the battery + to the monitor pin on the shield V2 will require an additional resistor for the Max voltage to be limited to under 5.5 volts at the voltage divider output.
With the formula: Vout=(R2/(R1+R2+R3)) x Vin where R1 is the 240 kohm resistor (R8 on the shield schematic), R2 is the 100 kohm resistor (R9 on the shield schematic), and R3 is the unknown value of the additional resistor needed to provide 5.5 volts or less on the output (Vout) when 25.2 volts Max is applied to the input (Vin).
Substituting these values we get 5.5=(100/(240+100+R3) x 25.2
We arrive at an "ideal" value for R3 of 118 kohms. The nearest GREATER value resistor (greater in order to ensure the voltage remains below 5.5 volts at Vmax), is 150 kohm.
Solving for Vout we get: Vout=(100/(240+100+150) x 25.2
Vout=5.14 volts
Therefore if I add a 150 kohm resistor inline with the battery when connected to the voltage monitor on the shield I should prevent the voltage of a 6s battery at Vmax of 25.2 volts from damaging the board.
Can someone confirm this for me??
BTW for those who have wondered, this tells us that the Max number of Lipo cells that can be used without the addition of an extra resistor would be 4 this would provide 4.94 volts at Vout
You need to be a member of diydrones to add comments!
Replies
Recheck the scematic.