How to measure DC current
I am wanting to measure some of the loads (amps) on my coach. My standard multi-meter does not support this. Thinking about options. What are you folks using and any tips on ways to get reli...
Forum Discussion
Do pay attention to specs if getting a clamp-on meter. Some only work with AC (depending primarily on how they detect current).
A traditional ammeter is often constructed of a millivoltmeter and a shunt resistance. If your multimeter can measure millivolts and you get an appropriate shunt, you can measure the voltage drop and find the current using math. A shunt is really just a low-ohm, reasonably high power resistor, with the resistance expressed as mV at some maximum current. A 50A 75mV shunt would have a 75 mV drop across it when 50A is going through it, which works out to a resistance of .0015? (1.5 m?) and a power rating of at least 3.75W.
I think most multimeters had at least some current measurement capabilities built in, though perhaps not the ranges that are useful for what you want to measure. Certainly both my Fluke 73 (a nice workhorse) and the super cheap generic analog meter (the one that stays in the RV) do: the former going up to 10A but no low-current ranges, the latter with only milliamp ranges.
A traditional ammeter is often constructed of a millivoltmeter and a shunt resistance. If your multimeter can measure millivolts and you get an appropriate shunt, you can measure the voltage drop and find the current using math. A shunt is really just a low-ohm, reasonably high power resistor, with the resistance expressed as mV at some maximum current. A 50A 75mV shunt would have a 75 mV drop across it when 50A is going through it, which works out to a resistance of .0015? (1.5 m?) and a power rating of at least 3.75W.
I think most multimeters had at least some current measurement capabilities built in, though perhaps not the ranges that are useful for what you want to measure. Certainly both my Fluke 73 (a nice workhorse) and the super cheap generic analog meter (the one that stays in the RV) do: the former going up to 10A but no low-current ranges, the latter with only milliamp ranges.
