question

Thanks, yes I understand Peukert is just a model of battery behaviour. I was more just getting my head around how the SmartShunt was actually calculating SOC. The manual and guides never actually say.

If it's just a straight exponential function and the exponent is based on C20 as a baseline value then I would expect C rates < C20 will see SOC fall more slowly than Ah discharge value might suggest.

I think what I'm getting at is the model probably has a domain of validity and a discharge rate of C200 is outside that domain.

I changed the exponent in the settings and will see how that goes.

C200 overnight it kinda normal as this bank is mostly designed for outage backup. But the plan is to add capacity and then begin to use it for more regular household loads.

Hi John, thanks for your comment/suggestions. I only just installed the Smartshunt the other day and the settings shown in the pic are Victron's default/recommended settings for the battery type, aside from the battery capacity I entered.

I figured over time I would work out what settings made more sense for my set up.

I changed the Peukert exponent yesterday to 1.13 and overnight the SOC has fallen more than the night before, and a bit closer to what I would expect based on the Ah discharged.

If the shunt expects a C20 capacity value (rather than the C10 value the batteries specify), then I can change that to the C20 specification. Depends on the end voltage used as my batteries gives specs for discharge to 1.75, 1.80 and 1.85 V/cell. The 1.80 V C20 rating for my bank would be 424 Ah (although they are not new batteries so who really knows?).

I agree with your comments about Charge efficiency, Tail current and CDT. I'm not as clear on the CV though.

Manual says CV should be 0.2-0.3 V below float voltage. They don't however say if that's per 12 V battery or for the battery total in series. Mine float at 54.0 V. If they mean 0.2-0.3 V per 12 V battery then the recommended 52.8 V makes sense, but if it's meant to be for the full bank then 53.7-53.8 V would make more sense. Not sure how this setting is going to do much as the battery is either charging or discharging, rarely resting.

Charge efficiency did seem oddly high to me. I might ease that back.

Tail, yes that seems high as well. I know after a decent float time my batteries settle into a tail current at ~1% of capacity rating. I guess I can drop that back to say 2%.

I'll increase the CDT to 10 minutes (longer?).

Of course these parameter settings will get tossed out the window when I start my experiment with a using a hybrid battery set up - I'll be adding some LiFePO4 to the mix and it will manage the bulk of the daily cycling when I start using the battery for managing general household loads, while the lead battery will just sit there on float most of the time, ready for backup duties.

It will be fun to see how it performs.
Cheers