I installed a SmartShunt to monitor the starter battery on a Ford Transit conversion I’m planning to take off grid for extended periods of time. There are a number of transient drains but the one I want to focus on here is a drain of 40 mA (as identified with a multimeter in series) when the vehicle is “asleep.” This is in good agreement with the vehicle spec of drain of no more than 50 mA. I performed a zero current calibration, to the best of my knowledge.[*] After doing this and reducing the current threshold to 0.01 A, I got a reading of 0.02 A for my 0.04 A drain – a 0.02 A underestimate. After 10 days this amounts to a 4.8 Ah error. If this error is used to calculate SOC, then it introduces an error of 14% into the useful capacity of my 70 Ah starter battery. Two questions:
(1) Is the 0.02 A error I’m observing reflective of the achievable accuracy of the device, or might I expect better by some tweaking of which I’m unaware or by swapping out devices?
(2) Is SOC calculated from the data displayed and will it therefore lead to the significant error I’ve described above (underestimate of 0.02 A leads to 0.02 Ah x 24 hrs/day x 10 days = 4.8 Ah/10 days)?
[*] Actually when clicking that button on the app, I got a warning to the effect that physically disconnecting the shunt was required; there were “cancel” and “ok” options associated with that warning box. When exiting the warning box by either route, I could perform no operation other than hitting the “calibrate” button again which again brought forth the same warning box. So I assume that choosing “ok” in the warning box implemented calibration. It would be nice to have this confirmed and even better to have a user interface that was not ambiguous in this regard (how about a “calibration complete” message – just a thought).