Posted on Apr 30, 2012 10684
The current range in multimeters, particularly the more inexpensive ones, is restricted by the load limits of the internal
shunts to 1 to 2 A. The figure shows how easily a precision heavy-duty resistor from Dale or RCL (0.1 ; 20 W; 1%) can be used as an external shunt. These resistors were not designed for this purpose, but they are much cheaper than custom-made shunt resistors. The 20-W rating applies only, by the way, if a heatsink is used: without that its rating is only 8 W. The maximum current through the device on a heatsink is about 14 A; the larger versions draw up to 17.5 A. When mounting the shunt, make sure that the test terminals (as well as the device terminals) are soldered properly, otherwise the resistance of the terminals is added to the shunt.