I am wondering why my SOC measurement is going down slower than expected, given that the Smartshunt can correctly see the consumption. This caused me to not notice my battery draining to zero.
As shown in the pictures below, I have a 400aH 48V bank and it’s configured as such. So consuming 100aH should equate to 25% SOC. In the week shown, the Smartshunt measured consumption going down by 100aH (-280 to -380), but the SOC in that time went from only 50 to 40 (10% difference for 100aH consumption, a scale of 2.5x off from what I expected). The starting percentage is off as well, because this offset had already been happening.
You need to read up on the Peukert effect. A simple overview is a 100Ah battery is specified to deliver 100Ah with a 5A load over 20 hours. With a 20A load it will deliver less than 100Ah and SOC will fall faster than Ah drawn. When drawn down slowly, say at 1A you will get more than 100Ah so SOC falls more slowly than Ah drawn.
The battery monitor allows for this so the SOC and Ah drawn may not necessarily be the same. This is set by the Peukert exponent setting and the effect is small for lithium and the Peukert should be set to around 1.05. The default for lead acid is 1.25. Good AGMs will be in the range of 1.10 to 1.15.
in your case, if a lot of the discharge has been at less than 20A then the SOC will be higher than the figure calculated from the Ah drawn. I see this effect on my boat where most of the discharge is lower than the C20 rate.the
What type of battery do you have and we can advise better battery monitor settings as your Peukert is default for flooded lead acid.
Thanks @pwfarnell. Someone on another forum pointed this out as well, and suggested to set it to 1.05, as well as change charge efficiency to 0.99 and lower my charged voltage to 56.
I have EcoWorthy 100aH 48V LiFePO4 rack batteries, so I believe this is mostly correct, the only thing I’m wondering is if I did actually have the “charged voltage” set correctly based on the specifications from the manufacturer below. They do not provide a separate “charged” and “max charging” voltage, just this number.
Is there any need to touch other settings (e.g. tail current, and current threshold)? I don’t see any recommendations from the battery manufacturer on those.
