Optimising SmartShunt settings

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Tom Ranson asked Feb 6, '23

Optimising SmartShunt settings

Hi all,

I am seeking some advice for optimising my SmartShunt settings, as the SoC reflected at present does not appear to be very accurate in my setup (SoC seems to be overly optimistic). I have read and re-read so many posts and watched many videos (including the Victron published ones) on this subject, however I am struggling to confirm the best practice values for my setup.

I have in an ESS setup:

- 8x Leoch DT126 240Ah (C20) FLA batteries in a 4s2p configuration at 24V 480Ah.

- SmartShunt 500A

- 2x MPPT 100/30

- MultiPlus ii

- Cerbo Gx

My questions only concern the settings on the SmartShunt. Please see the below image for my current settings, which I have determined from reading many different posts on the best practice configuration for the SmartShunt in my system design.

I so far believe I understand that:

- Charged Voltage should be set to 0.4V under Absorbtion (which is 28.8V on the MPPT's and the MP ii charger)

- Tail current should be set to somewhere between 1% to 6% (6% is a fairly high current though: 480 / 6 * 100 = 28.8A). 6% to me seems too high though, and will result in the SmartShunt resetting the SoC to 100% before the battery is fully charged (as it's still drawing nearly 30A)? Would a value of 1% be better? What are the pros and cons?

- Charged detection time of around 5 minutes.

- Charge efficiency factor of 80% (which is also set on the MP ii charger)

Here are my Multiplus ii and MPPT charger settings for reference:

I look forward to providing you with further information as required. Many thanks.

SmartShunt

screenshot-2023-02-06-10-06-26-94-30b6efbd53acd6f2.jpg (346.4 KiB)

screenshot-2023-02-06-111235.png (113.1 KiB)

screenshot-2023-02-06-11-13-53-61-30b6efbd53acd6f2.jpg (352.2 KiB)

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Answer 1 · 2023-02-06T12:29:57Z

michaeld answered · Feb 06, 2023 at 12:29 PM

Few things it could be:

I would drop the tail current down a bit. You could go as far as 0.5% (at least until the batteries age) but even on a long sunny day you might never reach it. Mine is set to 1.5% as a fair tradeoff with alternator charging in the winter (don't want to burn diesel for hours for the sake of a couple of amps), but you could try 1% and see if it reaches that every day.
Might be worth changing the peukert exponent from the default. You can calculate this using two discharge ratings from your battery's datasheet (pick one low and one high rating from the current range you actually use). My Leoch AGM batteries gave me a calculated value of 1.13 but I found 1.18 was more accurate.
Charge efficiency is a tricky one, as lead-acid batteries are close to 100% efficient in the bulk stage but this can drop to 50% towards the end of absorption. You basically want to pick a value that's about right for a whole charge cycle. I found 92% to be about right but obviously this'll be different for your batteries.

Ultimately if you don't fully charge your batteries every day the SOC % will start to drift over time, but playing with the above values you should be able to get it about right, definitely for daily cycling but at least for a few days after a full charge.

edit: while you're looking at the datasheet, make sure your absorption and float values are correct - they might be listed for cycle and standby use so choose as appropriate. Your SOC will be wrong if you're undercharging your batteries because the voltage is too low, and overcharging will reduce the capacity too. I actually knocked 10% off the capacity I entered into the smartshunt as they were cheap batteries and I'm not convinced they were 100Ah to begin with!

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JohnC ♦ commented · Feb 06, 2023 at 02:13 PM

Just adding a little.. If you decide to sync just under Absorb V, then it must happen before Float does. And the Tail A set appropriately (higher), Once in Float, a high CV can't happen.

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