The TK15 wattmeter is a very useful thing for monitoring the battery.

[capitancook]

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I did not find those who sell this in Europe
In my case:
General view - where did I install it


Wattmeter readings



The voltage and current measurement accuracy of TK15 is very high (IMHO ~ + -0.1%). It is only necessary to take into account that the accuracy of measuring the battery voltage using the DUE is not very high. In my case, the error in measuring the battery voltage is 26.19 - 25.94 = 0.25V.

Note, I changed the battery voltage measurement circuit. Diode D9 introduces non-linear errors in battery voltage measurements. So I cut the wire on the board PCB1.3 from R12 to the cathode of D9 and connected R12 to the anode of D9. In this way, the DUE measures the battery voltage without D9 non-linear error.

The battery current by TK15 s also measured very accurately (IMHO), but the current that you see in the monitor is equal to the sum of the currents consumed by the drive motors and the mower motor. The current consumed by PСB 1.3 (~ 0.2A) is not taken into account. See the code.

 

[capitancook]

I forgot to add - the voltage drop across the wattmeter shunt is very small (according to my measurements, ~ 0.001V / 1A), so it does not introduce any significant error in measuring the battery voltage with the PCB 1.3 circuit and the Sunray code.