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frenchie90 avatar image
frenchie90 asked

Consumed Ah Accuracy

Hi everyone,


I've been using the modbus shunt/inverter /mppt charge controller data in Home Assistant. The issue in having is the Shunt data for ConsumedAmpHours is dropping to zero suddenly as the battery starts to charge in the morning, this seems to coincide with the SOC jumping to 100%.

From reading online I might need to adjust the Peukert exponent value and charge efficiency, I've tried this but I don't really know what I'm doing with these values.


Batteries 8 x FullRiver DC400-6(AGM)

Victron 5kw MultiPlus Inverter

Smart Shunt 500A

2 x Victron MPPT Charge Controlers

6.6kw Solar


I based my Smart Shunt values on the forum post below and face tried to tweak from there:

https://community.victronenergy.com/questions/84530/victron-smartsolar15035-smartshunt500-for-fullrive.html

If I can get the ConsumedAmpHours to trend down all the way to basically to zero as the energy goes into the battery instead of jumping from say 50 to zero.

Any help/tips in greatly appreciated.


Thanks Eric

SmartShunt
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6 Answers
JohnC avatar image
JohnC answered ·

Hi @Frenchie90

The Consumed Ah while under discharge is likely a direct reading. But it won't necessarily match SOC, as Peukert sees to that.

When charging though, it must be corrected/estimated, as the V will be higher and there's charging losses too. It may actually be 'ratioed' directly to SOC when under charge, and it certainly drops to zero when the shunt syncs to 100%.

Your issue may be just premature syncing, as you mention this happening when "the battery starts to charge in the morning". This can happen when the Charged V is set a little too low, and/or the batteries get sluggish with voltage response in cold weather. If you have VRM, you should be able to work out why from the graphs. Look for the combo of Charged V, Tail Amps and Time.

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frenchie90 avatar image
frenchie90 answered ·

Hi John,


Thanks for the quick reply, I do indeed have VRM. Not too many graphs to look at in there but are these the ones you mentioned and if so it didn't appear to tell me a great deal when the jump happens, unless I'm missing something.


svid-20220906-070039-1.mp4 (7.9 MiB)
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JohnC avatar image JohnC ♦ commented ·

@Frenchie90

Yeh, I can't see anything either that shows there. Well done producing that too, but we can't be sure what 'System' means either, not knowing whether you're using DVCC or not. It's possible to concoct a custom widget, and there it will show the actual source of the readings. Here's one of my own today, zoomed and a couple of irrelevant curves blanked..

1662540502166.png

My sync point is set to 1.575A (% equiv), but VRM doesn't use that 2nd dec point. 99.9% and about to sync, then the black clouds arrived. Just showing you this for fun, and what you and others might use to track issues like this.

Alexandra is right too in asking for the settings in use. We're just guessing without them.

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richard-wright answered ·

I am new to Victron products and I have the exact same problem. My Consumed aH graph jumps from, say -50aH to zero within 15 minutes (the video above shows 3 minutes!) and yet the current being put back into the batteries at that time is only around 5-6 amps! Something is wrong here and I’m relieved I’m not the only one!

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Alexandra avatar image Alexandra ♦ commented ·
@Richard Wright

The batteries are synchronising too early to 100% so there must be something off in the settings.

Would you mind sharing them and your battery details?

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richard-wright avatar image
richard-wright answered ·

Thanks for the feedback. I’ll have to head back to the boat and pull out my settings for the shunt. But re-reading the sync criteria of 13.2v and tail current of 4% seems like my issue. With my Lithium batteries (608aH), I am always above 13.2v And most always below the 24a tail current. So this needs to be increased to around 14v and maybe 2% tail current.

On a second note, I love that graph with Current, Voltage and SoC all on the same graph. I see it is on your “DC system”. Can I get that just with the BMV-712 shunt?

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richard-wright answered ·

Found where to create that custom widget! Cool!

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richard-wright answered ·

That’s the solution! I increased the Voltage to 14v, the dropped the Tail current to 2% and increased the time from 3 minutes to 30minutes. Problem solved!0816b522-e2a6-4d4a-a696-7afd2685db7b.png


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