Most meters have a MAXIMUM amperage when used in series to test DC current and unless you buy a very expensive one, it will not be able to measure more than a few amps. To measure more than that a "shunt" is used and the amperage is measured off the shunt. (This one has a 10 amp setting)
NOTE - The link I posted requires a shunt above 10 amps
- Current range: 0~100A (requires an external shunt) (connect with 100A/75mV shunt) not included)
- More than 10A need external shunt
SHUNT AND WIRING CONSIDERATIONS (Extracted from the install instructions for my TM-2025 battery monitoring system)
A shunt (a very low resistance, accurate, high power resistor) must be wired into your battery system as described in section B of these instructions. This is how current (amps) and watts are measured by this meter: The “amps” shown on the meter measures whatever current passes through this shunt.
Therefore the shunt must be wired in series with the wire which carries the current to be measured. The shunt is almost always installed between the negative terminal of the battery and all the loads and charging sources (see Figure 1 on page 7.) It is located near the batteries, since the high current carrying wires must be kept short. The TriMetric measures the current ("amps") by measuring the very small voltage drop across this shunt. Watts measured by the meter are shown by multiplying the “volts” times the “amps”.
Shunt requirements: There are two choices of shunts which may be used: Most systems will use the 500 amp-50 mV shunt. For smaller systems you can use a 100A/100mV shunt (For this choice the meter must be programmed at Operating Level L3.)
Who might want to use the 100A/100mV shunt? (requires Operational Level L3) If you have an unusually small system that uses less than 70 amps maximum (charging or discharging) this shunt will show an extra digit to the right of the decimal point, and resolve currents as low as 1/100 amp. But the 100A/100mV shunt can get too hot with a typical 12V system with a 1000 watt inverter.
Technical note: Incidentally, it is only the shunt ratio between amps to mV. which is important to the meter--so, for example, a 200 amp-200 mV. shunt can, from the meter's point of view, be considered equivalent to the 100 amp-100 mV shunt. The implication, when a shunt is rated at "100 amps-100 mV." is that it may safely carry up to 100 amps maximum--however in many cases so-called "100 amp" shunts will not carry this much without overheating -- especially some of the "mini" shunts of this type.
This is what a shunt looks like and the amperage is measured using the small screws (a calculated number using the voltage drop).