SOC 90% setting

[gregoz]

I am trying to set my maximum SOC to 90%. I have charged up to 99% several times and the DSSR20s have turned off. I have 90% set in DMPPT section, yet every day I discharge and get down to say 88% SOC, it recharges up to 99%. Am I doing something wrong? Is there a setting somewhere else I have missed?

[Dacian Todea]

That is the correct behaviour. The battery will be charged once a day to full 100% and only subsequent charging will be done to 90%. So if you had any significant load so battery dropped below 87% then charging will start again and this time stop to 90% and so it will cycle there between 87% and 90% until the next day when a full charge is done to recalibrate the SOC and keep the cells balanced. 

[Patrik K]

So, if I for any reason want to have my batteries at 80% during winter, when I have very small loads, what settings can I do?

[Dacian Todea]

There is no option to maintain the battery at 80% as it is impossible to guess when you are at 80% without doing a full charge first and counting down the energy.

LiFePO4 has no problem being charged to 3.55V it is not like the other type of Lithium (NMC, LiCoO2) where charging to 4.2V (100%) will reduce their usable life.

[Patrik K]

Okidoki,
I guess I need to read up on the batterytype I’ve invested so much in. ;-)
My thoughts were that you saved on cyclelife by not keeping the battery fully charged, especially when there is very little load.
I guess that only applies for storage then...
Otherwise Im VERY HAPPY with my SBMS0/DSSR20 and I promote them every time I can on local Swedish forums :-)

[Allen Tindall]

I do not believe I have a problem, but I would like to explain my storage situation to make sure I should not be doing anything different to improve longevity of my 600 Amp Hrs 12V LiFePO4 batteries.  I store my RV under a raised Costco Tent and I live among some very tall trees so not much sunlight.  However, the solar panels do turn on in the morning and produce about 1/2 amp.  When I put the Motorhome in storage, the SOC varies from about 92% to 99% depending on what I have done that day.  I leave the Multi Plus remote panel switch in the charger only position but I have a switch connected in series with the EXIO4 that turns the Multi Plus charging off but leaves solar charging on.  In this configuration, shore power is feed thru the Multi Plus allowing use of AC Current without taking any charge from the batteries.  During storage, very small loads from the Multi Plus and from the SBMS0 are balanced with a very small charging current from the Solar Panels.  Unless I use the lights the SOC does not usually change much during storage.  The next time I take the Motorhome out, the solar panels will fully charge the batteries.  I have a switch in series with each DSSR so I have the ability to turn the Solar Panels off without turning the SBMS0 off.  Is the very small charging current from the Solar Panels, during storage, harmful in any way?

[Barry Timm]

I would wonder if it isn't best to lower your SOC% down to something like 70% while in this very light duty "storage" mode. My guess is that the batteries would be happier to be living down there rather than up around 99% for the majority of the time, while you're not using them.

[gregoz]

So I guess the next question is what maximum SOC should I set? I have it at 90% but I don't know now why I should. Is there no disadvantage to set it at 99%?

[Dacian Todea]

gregoz,

Because you only discharge down to 88% setting the SOC at 90% means it will only do a single charge cycle a day and that is all until next day.

In you case just setting that to 90% is a good strategy as since you use very little energy there is no benefit to charge the battery more than once a day or keep the SOC higher before night time.

[gregoz]

So we are trying to limit cycles. So lets say its summer here in Australia, and I have heaps of solar power, should I set it lower say 80% so that even if I use lots of power during the day it charges up only once? Better example - I go down to say 90% overnight but I know I will get lots of solar, so the Max SOC is set to 80%, I keep using power until it gets down to 77%, then it charges up once in say the afternoon because I have lots of solar. Am I getting it right?

[Dacian Todea]

gregoz,

The reset happens at midnight 0:00h and so as soon as the solar energy is available charging will start and charging will end when battery is full 100% SOC then charge will be disabled as long as the SOC limit set (-3%) is lower than actual SOC.

If say you set that to 90% and you get below 87% before the day is over then charging will be enabled again but this time charging will stop at 90% and this will repeat a few times if needed during the day.

But since you do not use much energy either during the day or during the night you have no reason to charge more than once a day that initial charging to full that is done to also calibrate the SOC.

So yes you can set that to 80% or even 70% if you want to make sure just one charge is done every day at the beginning of the day and no other charge cycle.

    

[gregoz]

OK I think I have this. So summer in Australia, I set it to 70% for example. I use power through the day say down to 75%. At midnight it resets, the next morning I charge up to 100%, but then I run down the batteries in the afternoon and overnight knowing that I can get down to 70% without it recharging. Next day it charges up again. So with enough solar in summer I can limit it to one charge cycle a day. Thanks.