SmartShunt with Lithims. How to go to 100% charge just on battery voltage?

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devodave asked Sep 12, '21

SmartShunt with Lithims. How to go to 100% charge just on battery voltage?

So I have 400A/h of lithium batteries being charged by 4 x Victron SmartSolar MPPT's and monitored by a Smartshunt. The MPPT's get the battery voltage via bluetooth from the SmartShunt, and they all have the following settings:

Absorption voltage 14.2V
Float Voltage 13.5V
Re-bulk voltage offset 0.1V
Absorptionduration Adaptive
Maximum Absorption time 0m
Tail Current Disabled
Temperature Compensation Disabled
Low temperature cut-off 5degreesC

My MPPT's happily all go to float the instant the battery voltage hits 14.2V. Good stuff.

The SmartShunt however doesn't recognise that the battery bank has hit 100%. My SmartShunt settings are:

Battery capacity 400Ah
Charged voltage 14.1V
Discharge floor 10%
Tail Current 4%
Charged Detection Time 1m

What do I need to do to make the SmartShuntconsider the batteries full?

Lithium Battery SmartShunt SOC

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pwfarnell answered · Sep 12, 2021 at 08:07 AM

For the shunt to go to 100% the voltage needs to be over 14.1A AND the current must be below 4% of 400A (battery capacity) = 16A. I expect that when you get to 14.2A and go to float, your current flow is still above 16A. Therefore, if you want it to synchronise you will need a higher tail current setting if this is the case.

Note also that as you have no absorption time, the batteries may not actually be at 100% when they go to float, you are going straight from bulk to float, hence the high current.

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devodave commented · Sep 12, 2021 at 10:07 PM

Cheers. I'll try bumping up the tail current each day to see if it thinks it's at 100%.

These are lithiums and there is no absorption stage. They get to the 'knee' voltage and charging must stop.

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wkirby answered · Sep 12, 2021 at 09:08 AM

Also, an absorb stage is necessary to give the BMS a chance to balance the cells.
A fairly high current at the 14.2V suggests that the battery is not quite full yet.

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devodave commented · Sep 12, 2021 at 10:09 PM

I have seen the tiny SMD components on the BMS balance boards and I don't think they are up to handling the 60Amps my 4 Victrons can put out. Happy just to end charging at the knee.

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Answer 1 · 2021-09-12T06:47:26Z

Bob K answered · Sep 12, 2021 at 06:47 AM

I synchronized the SOC to 100% with the app after I was sure that the charger had fully charged the battery bank. Section 5.3 in the manual:

https://www.victronenergy.com/media/pg/SmartShunt/en/operation.html#UUID-b46e8c9c-ade6-43c6-a192-d7fcd84e12a7

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devodave commented · Sep 12, 2021 at 10:05 PM

I can do that manually, but I was hoping for the SmartShunt to do that itself. I'm going to attempt to raise the Tail Current to see if that helps. Thanks.

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Answer 2 · 2021-09-12T07:26:15Z

klim8skeptic answered · Sep 12, 2021 at 07:26 AM

Victron has a quite useful BMV Youtube tutorial.

Might be worth a look.

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devodave commented · Sep 13, 2021 at 01:02 AM

Checked it out. Loved the accent.

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