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xpatrik avatar image
xpatrik asked

SmartShunt 500A Wrong SOC - Lithium Settings?

Hi, My smart shunt's SOC is very inaccurate. Today battery was nearly charged (less than 0.5v from full chraged voltage and current was around 1A) and the shunt was reporting 50% soc (Last full charge and sync to 100% was 4 days ago). My battery is a Li-Ion 18650 build with 14s20p 20AH in total usable.

Not sure if this helps but this is my vrm share link: https://vrm.victronenergy.com/installation/191449/share/6b42df03 maybe someone can tell whats wrong...

Also my other devices in system are:
RPI 3 Venus device
MultiPlus-II 48/3000/35-32
BlueSolar Charger MPPT 150/45 rev3

Here are my current settings:

shunt-settings.png


Lithium BatterySmartShunt
shunt-settings.png (46.5 KiB)
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Trevor Bird avatar image Trevor Bird commented ·
@xPatrik is your battery capacity really only 20Ah? Seems very small to me. Have I missed something?
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xpatrik avatar image xpatrik Trevor Bird commented ·

No you didn't miss anything It really is only a 20AH battery. It used to be a 12v 3s pack but i rewired the packs to be 48v 14s. To use with a 48v multi (I'm planning a battery upgrade to LiFePo4 105Ah cells but they are currently out of stock so thats why im using this small battery)

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Trevor Bird avatar image Trevor Bird xpatrik commented ·

@xPatrik They must be very small batteries. I thought they would be about 2Ah each… 20p doesn’t that make it 40Ah?? Seems too low for 20p.

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xpatrik avatar image xpatrik Trevor Bird commented ·

The cells are 1.7ah each. but i do have one weak pack so thats why its 20ah

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5 Answers
Alexandra avatar image
Alexandra answered ·

@xPatrik

Is the charged voltage you set your bulk or float charge?

Here is how to set that correctly. (Hint 0.2 or 0.3 under float.)

And 2% as your tail current, of 20AH is 0.4A.

To trigger full, you have to get above the 58.6v and have a tail current drop below 0.4A for 3 min (charge detection time)

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xpatrik avatar image xpatrik commented ·

My float voltage on my solar charge controller is set at 58.7V. Also my problem is not that the shunt doesnt sync the soc to 100% it is just if i do not full charge cycles after 4 days you see the soc is not accurate at all.

Edit: Ok so i did change the charged voltage to 58.5 But that still doesn't fix my issue of the soc not being accurate when not doing full charge cycles.

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ludo avatar image
ludo answered ·

Check your connections and post a drawing of your wiring. In my experience one or the other minus is connected to the wrong side of the shunt.

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xpatrik avatar image xpatrik commented ·

This is what is my current setup. No dc loads just shunt,multi,solar controller,bms (bms does not communicate with the raspberry pi) Current reading from shunt are good but the soc after just a few days is wrong

1664745881773.png

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1664745881773.png (5.2 MiB)
ludo avatar image
ludo answered ·

Ok, now for the next cycles forget the pi, check your status on the smartshunt.


No load at all? This is getting stranger by the Minute.


Where is the pi connected ?

In earlier posts you mentioned a multi ?


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xpatrik avatar image xpatrik commented ·

Sorry for confusing you, The multi has Ac Grid and Ac Loads connected but there aren't any DC loads other than multi. But the soc is still wrong after a few days without syncing. I'm not sure if i have something set up wrong or if its the shunt settings that makes the soc not accurate

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ludo avatar image
ludo answered ·

Where is the multi connected, pls include in the drawing.

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xpatrik avatar image xpatrik commented ·

Multi and Mppt are connected to the bus bar like this (There is ac wiring on the multi but is not shown in this picture)1664804108330.png

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1664804108330.png (5.2 MiB)
JohnC avatar image
JohnC answered ·

Hi @xPatrik

I just took a look at your VRM. My, you're sure working that little batt hard at times. Like at up to C3 discharge rate. This means you might need to give the Peukert Exponent setting some attention. The higher the PE, the more 'penalty' will be applied to the SOC, so over a period that will accumulate and show an SOC lower than it really is.

Try lowering PE and see if that improves things. After some discharge you can actually change this around and it will recalculate SOC. Try it and see if you can get a feel for it.

With such a small batt and heavy cycling, tuning this system will be more difficult than most, so you'll need patience..

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xpatrik avatar image xpatrik commented ·
Okay, I lowered it and im gonna recharge the battery thonight and test if the soc is correct. Also i dont think im discharging at 3C im usually max 700w load so 0.75-1C max
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