ESS State of charge limit suddenly becomes a problem as we get more sun in spring

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shbs asked Feb 17, '24

ESS State of charge limit suddenly becomes a problem as we get more sun in spring

I have a Multiplus II 5000, 8kW solar panels and 14.4kWH of pylontech batteries.

All winter I have been charging the battery at night to 95% and using this power during the day. Occasionally the battery goes down to 15% and we start using mains power as expected.

Now we are getting more sun and the charge is staying up pretty high during the day so I reduced the night time charge to 80%. Today I noticed that the battery was at 80% and not discharging and we are using mains power. I checked the ESS settings and noticed that the Active SOC limit was at 80%. I have no idea what it was before but the system worked as I expected, discharging the battery each day and charging at night.

I changed the Battery Mode to - Optimized (without BatteryLife) and the battery started discharging.

Can anyone tell me why this has happened?

ESS

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Answer 1 · 2024-02-17T18:38:54Z

nickdb answered · Feb 17 at 06:38 PM

You’re limiting the battery from fully charging, so batterylife will keep raising the active SOC. The battery needs to hit 95% or more to lower the limit.

Its not a great process you’re using. It will limit the battery’s ability to balance and thus hit 100%.

Disable batterylife if you insist on using this method.

It is designed to get the battery to 100% every day, something you are preventing.

Those batteries are designed and warrantied for a full charge. You are not accomplishing anything by limiting it, if anything you are doing more harm than good.

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Answer 2 · 2024-02-17T18:45:24Z

shbs answered · Feb 17 at 06:45 PM

Thanks nickdb, that's good to know.

There's always that nagging doubt in the back of my mind that fully charging a battery can't be good for it. This mainly comes from the advice for keeping our electric car between 20 & 80 percent.

How do you recommend I transition from charging from the mains in winter to charging from the sun in summer?

Stuart

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daza commented · Feb 17 at 06:50 PM

Are you on solar export? Most electric cars are not LFP which is a different chemistry they are starting to come through though.

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nickdb ♦♦ commented · Feb 17 at 06:56 PM

Don’t cap the soc, let it fully charge and let batterylife do its job.

It works and you won’t hurt the batteries.

Pylons are the most widely installed, with an enormous base of data showing that they will last if you just let the BMS do its job, something it cannot do if you limit soc.

Use the force :)

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Answer 3 · 2024-02-17T18:47:59Z

daza answered · Feb 17 at 06:47 PM

As @nickdb said charge them to 100% you a clipping the batteries and that's not good you will start to see cell imbalance as your not allowing it to hit 100% to balance all the cells. Just leave it you obviously not gong to use 100% of the battery so you will have X percent leftover everyday better have over this end than not balancing the cells. Why are you only charging to 95 or 80 percent @SHBS ?

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Answer 4 · 2024-02-17T18:59:24Z

shbs answered · Feb 17 at 06:59 PM

I am on the FIT tariff and export very little so not worth going for an export tariff. I charge the car and heat water in the summer with PV.

I only charged to 95% during the winter as I thought that best but now stand corrected.

Ideally I would like to start reducing the night time charging as I get more sun during the day . When I installed the system last summer I had plenty of solar and never charged at night but in October the solar plummeted and I started charging at night. As far as I know, I was able to discharge the battery fully last summer and didn't realise the Active SOC limit even existed.

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daza commented · Feb 17 at 07:45 PM

@SHBS yeah winter months is the pits ive just got another 4.8kW pylontech to see me through winter no sun today and i'm at 49% so this will last out my peak rate and then sum so i start using off peak to charge the batteries through out that whole off peak period so it can balance fully and keep it there for a while and just keep the whole house using the off peak as i'm running two dehumidifiers at night so don't what the battery to be eaten up on that.

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