I bought three of these. A pair of meters is connected to the same shunt for both charging and discharging, as shown in the supplier's diagram. The third counter measures only the summary of the solar panel charging data. If the sum of the two charging counters Wh is equal to or greater than the discharging counter Wh, then the batteries have not lost any capacity. If/when the discharge counter is greater than the sum of the two charge counters, then the batteries have a reduced capacity and need to be recharged. I have read all the reviews and one in particular is misleading, from DLH. He claims to have "cured" the problem by installing a 50amp/75mV shunt. This doubles the meter reading since the scaling factor is half of 100 amps. It's not a cure at all. Only a 100A 75mV shunt can be used with this meter. He also worked within half a percent of full scale. Although the shunt is designed to be 0.5% accurate, it's a bad idea to run that current near 0%. I have calibrated MICTUNING gauges with various expensive VOMs and have found them to be fairly accurate. The price of this system is pretty fantastic. Another review states that the shunt is for the backup function. Not true. Some shunts are specifically designed as fuses, but this shunt is for measurement, not protection. The power consumption of the meters is actually much lower than stated. All three meters consumed only 0.11 watts when the light was on, and a third when the light was off. Well done MICTUNING. See photo.
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