Mini 0.28inch LED Digital Voltmeter Ammeter DC 100V 100A Volt Ampere Meter with Shunt.Small size, portable and the magnitudes of voltage are displayed in the same screen simultaneously. 

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Normal voltage display, current display 0.00 or 0.0 :Make sure the thick black wire is connected to the negative post of the battery and the thick red wire is connected to the negative post of the load. (Please note that the discharge is not the same as the charging connection) ( if Current display shows 0 99.99% then there is wrong wiring, please check the wiring carefully)   The current display is inaccurate:If it is a direct power supply or an independent power supply and the device power supply is common ground, as long as the thin black line can be cut off accurately. Power connection is not displayed: All AC power must be filtered with an electrolytic capacitor above 1000 μF to supply power to the meter.Connect the shunt, connect the thin red line and the thin black line to the power supply. 100A wide spectrum current meter shows 0.00.
Other considerations:

• Current can only be measured on the negative side of the power supply and on the negative side of the load.   
• Voltage range: The supply voltage range of 5 line headers is 4 ~ 28V, that is, the voltage of the thin red line can not exceed 28V.