Ammeters
Attention:
1,999mA, 2A, 5A, 10A, 20A,the shunt is built in.
2,More than 20A ,you must use a shunt to work,even 0.1A, or it will be burnt.
3,More than 20A,the shunt is not built in

4,Because the 24V battery charge full of floating voltage may be more than 30V, so "no" recommended direct use 24V battery.
5,In the following circumstances, it is strongly recommended to choose: isolation meter (isolated power supply meter):
(1) When two or more meters are installed on a device. (2) Can not be isolated power supply.

Features:
The wide power supply range, with reverse polarity protection.
Display voltage and current on the screen at the same time.

Meter power supply: two-wire terminals
Black wire: Negative power supply.
Red wire: Positive power supply.
Testing side: three-wire terminals
COM: Test common terminal(The COM is commond negative of voltmeter and ammeter)
V +: Test positive voltage input
A +: Test positive current input. It can only be connect the load negative and load power negative
Suitable for "20A or less",no need a shunt:
Suitable for "more than 20A ,must need a shunt: