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I have 2 - 225ah 6v golf cart batt in series. My SOC is 85% and voltage is 12.09 as seen in this screenshot. Looking at the typical charge chart for voltage my battery should only be slightly Over 50%! Is there something wrong here? What am i missing.Screenshot_20210615-060831.png
If they are lithium then voltage does not mean much. If lead acid then a bit better. But if the system is under load then the voltage means nothing as voltage drops with load.
working with a shunt or bmv is more accurate when the settings are good. In your case it is possible that they have not been getting to 100% or absorption each day for their type (moving through bulk absorption and float cycle)? Will need more info to work it out.
Thank you. I am trying to understand how dc systems work as it does not come easy to me. I will put this on ac to charge up batteries for next couple days and take s look again at my numbers. These Readings have been like this after camping 2 weeks in almost full shade with only generator to charge up to 100% soc and voltage to 13.4. By next am I'd be at 79 %soc. And 11.93 volts and would recharge. My dc fridge takes a heavy toll. Your explanation therefore makes sense.
Is this guide any help?
I've got 460ah available and am showing 67.5ah consumed. That's 86%. SOC currently shows 90%, so that's at least pretty close. Voltage (under light load) is, of course, 12.5v which is not particularly helpful.
But is SOC really correct? If I use half my amp-hours would SOC show 50%?
If you set your Peukert Exponent to 1.00 then you'll get a closer match. But then the SOC won't be correct, unless you have 'perfect' batteries. And you don't..
What's an Amp-Hour contain in energy anyway? Varies with Voltage, and not many batts charge and discharge at the same V.
So you have to trust a little, understand, and get your settings tuned in. The Victron shunt based devices can be very accurate for SOC if set up correctly. They don't use direct V or Ah readings to do that though.
And that's fine. But you must understand that Peukert is altering the SOC to compensate for the batt discharge rate. So the Ah won't be equivalent to SOC.
This is deliberate of course, a feature. Have trust.. :)
I guess my big question (If I were to correctly phrase it) is - can I trust my SOC readout?
When I had only two batteries I would routinely hit 75%, sometimes lower. I was also attempting to power some things I shouldn't have, forgetting to switch things to gas, etc. Also clouds. Now that I have four batteries I rarely drop below 90% before the next day's sun hits the panels. So I guess the SOC is pretty accurate?
