question

cameron moodie avatar image

Batteries show full chage on Mulimeter, but SOC says less than 30%

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Hi all, I'm have some issues with the way my setup seems to be reading the SOC for my battery bank. the system seems to be saying that I only have a 30% SOC however when I test the individual batteries with my Multimeter they all have 13.5v which I beleive means they are at 100%? is there something I need to reset within the system?


System set up as follows:

Off-Grid system

Product MultiPlus-II 48/3000/35-32 (ACOut2 switchable)

Firmware version 478

SmartSolar Charger MPPT 150/70 rev2

Firmware version v3.07

battery bank made up of 2 parallel banks of 4 12v 100ah Lithium-ion batteries

using a

Color Control GX

Firmware version v2.73



Lithium BatterySOC
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1642893864942.png (1.9 MiB)
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2 Answers
kevgermany avatar image
kevgermany answered ·

Short answer, without a shunt and battery monitor the system can't give very accurate readings. The BMS in your batteries may provide this, if they're on the compatible list it may be possible to use this value in the system. So shunt not needed.

But this is too far out. You can synchronise to 100%. But also I suspect your charge parameters are not set correctly. Also that it will continue to drift down.

P lease add a screen shot of the charge settings

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@cameron moodie

They will only be considered fully charged if they have hit the absorption voltage (usually mich higher possibly even around 14.2v )and dropped back down to float at the 13.5v.

Knowing what batteries exactly you have is also useful information as each manufacturer has different recommended settings.

cameron moodie avatar image
cameron moodie answered ·

@Alexandra Thanks for the reply, the batteries I am using are Voltx Lithium 12v 100AH. specs are below:

SPECIFICATIONS

Nominal Voltage: 12.8V

Usable Capacity: 100Ah

Energy: 1280Wh

Charge Voltage: 14.6V

Charge Method: CC/CV

Charger: 14.6V 20A

Standard Charge Current: 50A

Max Charge Current: 50A

Standard Discharge Current: 50A

Max Continues Discharge Current: 50A

Max Discharge Current 5 sec: 100A

Life Cycle: Approx. 2000 Cycles

Working Temperature Range: Charge: 0°C to 45°C

Discharge: -20°C to 50°C

Storage Temperature: -10°C to 50°C

Battery Cells: Prismatic

Bolt Type: Hexagon

Bolt Material: Iron nickel-plated

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@cameron moodie

So SOC must be fairly close to right, especially if it did not reach the target 14.6 per battery then drop down again to float. If your float has even been set at? And is the system reaching the full charge amount first?

Your batteries should reach at least 14.6v per battery or 58.4v for the bank total. 54.18v is far from full lithium have a pretty flat voltage curve.

With it being offgrid I can definitely say if you are not reaching the full 58.4v for a period of time like maybe an hour each day, your batteries are nowhere near full or will remain balanced in the bank. And the system will have a hard time calculating state of charge. It will be worth adding a BMV or shunt and maybe some balancers.

Pro tips! thank you! I have ordered a smart shunt to add to the system but feel I may need to alter the programming on the mppt to reflect what I am trying to achieve... I'm assuming I can set the solar charger to reflect the needed voltages and such... im still kinda new at all this so learning a lot as i go.
@cameron moodie

No stress. I learn new things here everyday. And we all started somewhere....

So, at risk of sounding ignorant... If the full voltage is 14.6 X 4 or 58.4v what would the float voltage be? Or is it the same thing?

@cameron moodie

The float can be what you like. I did not see a specific setting stated for your particular batteries. Some say lithium doesnt need a float charge. Generally one or two volts lower is ok. The ones I have in my systems are more specific in their settings as they have partnered with Victron.

Bear in mind the lower you float the less capacity you have stored in the bank.

So these are the settings I have Entered I to my solar charge controller based 9n my battery specs.

screenshot-20220125-152240.jpg

@cameron moodie

Neat. Keep us updated if you run into issues at all. We will be keen to help you tweak the settings. If you use the @ then I will get a notification in the email and not miss it.

@Alexandra Thanks for the support. I've set the float to 56v and the rebulk offset to 0.01. so hopefully this will allow it to get get to the absorption phase which is hasn't done for the past couple of days.

@cameron moodie

It is possible you have insufficient solar right now.

I estimate 10kwh of battery in your bank, if you are at 30% then your solar charging it at 12A (information from your post) you would not get to full charge in the day unless you have over 14 hours of full sun, maybe see if you less on AC side for a few days and see if that helps. Or add more solar.