On a 24v lead acid battery bank (1 x 12 batteries connected with 2x70mm2 wires to each other) I have plugged (with the Victron supplied cable) the midpoint to the positive terminal of the 6th battery.
With a decent multimeter (whose measures vary only 0,01V from the Shunt BTW) midpoint readings (bat. 1 to bat. 6 and bat. 7 to bat. 12) are the same to a hundredth of a volt (x,xxV).
According to the SmartShunt 500A, though, top voltage is on average higher ~0,04 volts than bottom voltage.
I have also noticed that with bottom (midpoint) unplugged (where the readings ought to be 0v and variation 100%) the SmartShunt calculates a Midpoint Deviation of 100,2%.
I am figuring this falls within the 0,3% claimed accuracy of the device.
Anyway, shouldn't we be able to manually enter a compensation/correction factor somewhere (e.g. on one side we have 24v on the other 12v, certainly the drop along the wire must vary a tiny bit - does the Shunt compensate for this)?
Also, in the documentation, Victron claims this to the formula used for midpoint deviation %:
Where:
d is the deviation in %
Vt is the top string voltage
Vb is the bottom string voltage
V is the voltage of the battery (V = Vt + Vb)
This would presume that a Vt is monitored independently of the Vb, which in fact does not seem to be the case. Most likely Vt=V-Vb
So, does anyone know how exactly is the SmartShunt calculating Vt? Is it, in fact, a simple case of d=100*((V-Vb)-Vb)/V?
