maidbythesea avatar image
maidbythesea asked

Restricting charging

We’ve just installed 660Ah LFP/LifePO4 batteries and the maker suggests charging them routinely up to 90%. We have 420W of solar panel connected through a Smartsolar 100/30 MTTP controller. This is set to the Lithium setting with everything else set to defaults. We also have Multiplus inverter/charger which is also set to the lithium defaults (as far as I know). Naturally, we can switch the invert/charger off at any time but is there a way to tell the Smartsolar to only charge up to 90%? We have a similar issue with the Balmar alternator voltage regulator but that’s another story.

smart solar charging behaviour
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1 Answer
Alistair Warburton avatar image
Alistair Warburton answered ·

There are settings for that in the Multi, State of charge when bulk finished being the one you are initially interested in I think.


You then need to decide what you are doing with absorb and re-absorb...


Ignore my settings, they are just limits, the BYD BMS controls all charging using DVCC.

and you could definitely do it by capping the bulk terminate voltage lower but if it were me I would be actively driving the charge current limit using Large OS NodeRed. Doing it that way give you full control so you can periodically charge to 100% and then absorb/float, same thing for LiFePo4, which gives the BMS headroom to balance.

Bear in mind that the SOC is based on counting energy and will drift over time because very low loads, in or out, don't get counted. What is and is not counted will depend on what, if any, external battery manager you are using.

It isn't unusual to see a pack jump from 80% or 90% to 100% because the SOC was being under reported in the first place due to long periods of low solar input.

I have my capacity, Ah set to less than is physically installed so that 0% isn't actually the point at which the internal BMS cuts the output.

I have also been thinking about having node red compare terminal voltage, lode compensated, preferably by the flow learning what volt drop is expected for a given load, so it can warn me if the SOC suggested by the voltage is significantly different to the Counted SOC in the Victron system.

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