Is this SOC correct?

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stevet asked Feb 21, '23

Is this SOC correct?

Using the SmartShunt on dual 6v 230Ah batteries connected in series in my motorhome. Using VictronConnect to monitor the batteries. The batteries were only a couple weeks old and 100% charged when I installed the SS. We use the batteries to supply power for heating, lighting, electronics, etc. while boondocking. I have been monitoring the batteries while our motorhome is in storage. Today here's what VC reported. Does it make sense that VC is reporting my batteries have a SOC of 100% when the voltage is only 12.47?

SmartShunt VictronConnect SOC

screenshot-20230220-161401.jpg (75.6 KiB)

screenshot-20230220-161342.jpg (126.3 KiB)

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Answer 1 · 2023-02-21T04:17:19Z

kevgermany answered · Feb 21, 2023 at 04:17 AM

The shunt can only measure current through it. It cannot account for self discharge within the batteries.SOC is based on current, not voltage. Shunt resets SOC to 100% to correct for drift, but only when batteries fully charged.

So the reading makes sense - in terms of how the shunt works. But is misleading.

It would be good to charge the batteries every month or so while it's in storage.

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Answer 2 · 2023-02-21T07:18:17Z

JohnC answered · Feb 21, 2023 at 07:18 AM

Hi @SteveT

I agree with Kev, but your shunt settings probably could use some tuning too. Depends on your batt type, but we may be able to help if you ask.

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Answer 3 · 2023-02-21T14:19:16Z

stevet answered · Feb 21, 2023 at 02:19 PM

Should have mentioned the batteries are Napa lead acid deep cycle golf cart batteries. This is all new to me. I did a lot of reading on how to setup the VC app. Admittedly, I did not understand everything so I just kept most of the default settings. Suggestions are welcomed and appreciated. I will charge them up today. So I should just charge the batteries based on the reported voltage and not worry about SOC when the batteries are not being used?

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JohnC ♦ commented · Feb 22, 2023 at 03:07 AM

@SteveT

Are they these generic GC2's? https://www.napaonline.com/en/p/BAT8144?impressionRank=22

If so, I use clones of them, and these my shunt settings (for 48V)..

You could raise Tail a little if you have short days or poor solar (so you mightn't reach it), say up to 1%. The 'true' Peukert of mine is 1.16, but I use 1.10 because it seems to work better at my lowish loads. The low 87% CEF is my summer setting (Pb's aren't efficient topping off a shallow discharge), but maybe 91% in winter. By all means tune them to suit yourself, but these will be better than the all-encompassing defaults.

I don't look at V much, Amps they can accept under charge is more important. These batts are quite reactive as Pbs go, and I find that 7A at Absorb V is 99.0% charged (and a good place to end Abs and drop to Float). In Float, that's my 0.6% (~1.3A), and then they're 100% SOC.

My charge settings (in your 12V lingo) are 14.4V Abs, 13.6V Float and -25mV/degC TempComp.

Mine are daily cyclers, not stored. But if they were, I'd give them a charge dose every coupla weeks. Electrolyte stratification and sulphation your enemies. They'll appreciate a little exercise, hey..

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stevet JohnC ♦ commented · Feb 23, 2023 at 01:06 AM

Yes, the Napa 8144. Thanks for the suggestions. I will play around with the Tail and Peukert. Is your Charge Efficiency Factor at 87% because your batteries are older?

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JohnC ♦ stevet commented · Feb 23, 2023 at 03:58 AM

@SteveT

Age might have a little to do with it, they're ~6yo, beyond 'budget' expectations. But they're only drawn down to 80%, and I expect to have to raise CEF when I draw down deeper in winter (and they get cold). I'll know when to do that when the shunt needs to sync every day, because the indicated SOC hasn't reached 100% with the low CEF.

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nesswill commented · Feb 22, 2023 at 06:55 AM

Completely agree with JohnC on this and as he says once you have "lived" with your system for a while you will get to know it and make small changes to optimise it for how you use it.

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