One additional comment: If measuring amphours is important, the E-meter / Link-10 / Link-Lite is the way to go. They have an exceptionally accurate circuit for measuring the voltage across the shunt to determine current.
A shunt is basically just a precision resistor. A typical shunt has a voltage drop of 50 mv at 500 amps, which means it is a 0.0001 ohm resistor. At 1 amp, that means the voltage drop is just 0.1 mv. You need an amplifier to boost this to a measurable level. But most opamps have input offset errors of several millivolts. A 0.1 mv signal gets lost in the noise. A 1 amp error when measuring current usually isn't that important. But to measure amphours, the error gets multiplied by time. A 1 amp error in measuring current means an error of 24 amphours per day. And it keeps accumulating every day! Most inexpensive meters thus have a threshold below which they assume the current is zero. That way, the displayed amphours won't accumulate when the vehicle is parked due to errors in the meter's current measurements. But it also means the meter won't accurately display amphours due to small loads or charging currents. The E-meter family uses an expensive ZERO offset opamp in its current sensing circuit. Its worst-case input error is two orders of magnitude lower than that 0.1 mv signal from a 1 amp current. -- Excellence does not require perfection. -- Henry James But it *does* require attention to detail! -- Lee Hart -- Lee A. Hart https://www.sunrise-ev.com _______________________________________________ Address messages to [email protected] No other addresses in TO and CC fields HELP: http://www.evdl.org/help/
