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Elimac avatar image
Elimac asked

End of absorption with tail current

Hello. I wonder if I am thinking this right... I am trying to end the absorption phase solely based on the tail current, but it seems system is ignoring that.


Scenario is: Charging LiFEPO4 bank with 8 cells (25.6V) with integrated BMS just for protection (no communication with Victron)

- Multiplus 24/ 3000

- 3x MPPT in parallel charging

- Venus GX


Customised charge profile:

- Absorption voltage: 27.6 V (I can monitor cells, and no cell is above 3.6V)

- Absorption time: Fixed, 1hour 30 minutes

- Tail current: 9 amps, battery capacity is ~180Ah

- Float voltage: 27.1 V


It ignored the tail current and the absorption time was exactly 1,5 hours. I would like to stop absorption when current decreases past 9A.

I didn't feel adaptive time was ok for lifepo4, as if bulk takes longer, absorption may not need so much time. I would like to make the criteria to stop Abs be solely the Tail Current (system!, not individually each MPPT)

How can I do this?

battery chargingLithium Batterymppt charging
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2 Answers
Mark avatar image
Mark answered ·

I have been using tail current to end absorption phase for some time now and it's been working very well.

I initially used the solar charger output current and then switched the DVCC - SCS when the feature was released with the BMV battery monitor as the tail current source.

However I have a single large MPPT, so it might be a compatibility issue when using the tail current feature with multiple MPPTs in parallel - linked by VE.Smart Network.

I will try to find out for you.

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Elimac avatar image Elimac commented ·

Mark, is the presence of the BMV a mandatory condition? As System current is already known in my case, even without BMV, I was hopeful it wasn't needed. But, in SCS I can't detect any monitor...

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john-hagtharp answered ·

Are you running ESS & DVCC? If my understanding is correct, this would place the MPPTs under external contol using the charge algorithm from the Multiplus.

Unless I missed something in the changelogs, I don't believe you can set a tail current in the Multiplus. Adding the new charge algorithm capabilities from the MPPTs into the Multiplus is something I've been meaning to request some time.

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Elimac avatar image Elimac commented ·

Only DVCC (mainly due to the charge current limit necessity). No ESS, it is a (nearly) offgrid system.

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