Battery shunt resistance?
I've been getting some wacky readings from my power meter. I'm wondering if the shunt is bad and wanted to see if it can be checked by measuring resistance? It is a 75mv shunt. Thanks!
Forum Discussion
You need to know the current rating of the shunt as well as its design voltage to figure its resistance; at that point, it's just an application of ohm's law.
If, for instance, it's a 100A 75mV shunt, then .075V = 100 R, or R = .00075 ohm ( that is 0.75 milliohm). Very few multimeters will measure that; the minimum resistance range on my Fluke 73, for example, has a precision of 0.1 ohm.
Before completely blaming the meter, see what it reads with the input short-circuited. With an open circuit input, it may be picking up enough stray charge to read most anything (particularly if it's a digital meter). Checking the calibration of it would be easier by applying a known test voltage in the 0 to 75 mV range.
It's possible for poor contact at the shunt connections to lead to incorrect readings at times, too.
If, for instance, it's a 100A 75mV shunt, then .075V = 100 R, or R = .00075 ohm ( that is 0.75 milliohm). Very few multimeters will measure that; the minimum resistance range on my Fluke 73, for example, has a precision of 0.1 ohm.
Before completely blaming the meter, see what it reads with the input short-circuited. With an open circuit input, it may be picking up enough stray charge to read most anything (particularly if it's a digital meter). Checking the calibration of it would be easier by applying a known test voltage in the 0 to 75 mV range.
It's possible for poor contact at the shunt connections to lead to incorrect readings at times, too.
