MPPT with BMV - Which Tail Current will it use for Float? 4% or 1 Amp?

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thorvald asked Oct 5, '20

MPPT with BMV - Which Tail Current will it use for Float? 4% or 1 Amp?

I have a simple test setup with an MPPT 100/15 and a SmartShunt 500. Bluetooth Smart Networking is enabled.

It has a pair of 79Ah AGM batteries in parallel (158 Ah in total at 12v)

It is charging via two 150W Solar panels in Series.

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With regards to the MPPT and the BMV in Bluetooth Smart Networking mode, how does the MPPT know the battery is ready to go into float mode using Tail Current?

1. The MPPT says it waits for 1 Amp draw of Tail Current (default value)

2. The BMV/SmartShunt Tail Current says it waits for 4% of the total battery capacity (158 Ah, Tail Current 4% so should be 6.32 Amps).

Obviously there is a huge difference here. 1 Amp vs 6.32 Amps.

Questions:

1. Does the MPPT use the BMV/SmartShunt (with SmartNetworking enabled) Tail Current 4% value for detecting when to move into Float mode?

2. If the MPPT does not, should I change the tail current of the MPPT from 1 Amp to 6.32 Amps to ensure I don't over charge the batteries in Parallel?

3. With batteries in parallel, do we need to double the tail current value in the MPPT? (i.e. running from 1 A tail current to 2 A)?

Thanks

MPPT Controllers

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ishtiaq commented · Dec 04, 2020 at 10:30 PM

I do have the same concerns about the tail current on MPPT and BMV, lets wait for an expert feedback on this topic

thanks

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Answer 1 · 2020-12-05T11:26:21Z

JohnC answered · Dec 05, 2020 at 11:26 AM

Hi @Thorvald @Ishtiaq

The Tail setting in the BMV (in %) is used solely for synchronizing the BMV. It doesn't relate directly to the mppt.

The Tail in the mppt (in Amps) can be used to change from Absorb To Float. In Expert mode, (maybe set to a Fixed Abs Duration), the Tail Amps can be set there. If not networked it will use it's own Amp reading, and drop to Float when that is met.

If networked, the mppt can then use the Amp reading from the BMV instead. But it will honour the Tail set in the mppt.

Again, you have two Tails (makes for a happy dog), and each serves a different purpose..

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Answer 2 · 2020-12-05T14:23:37Z

ishtiaq answered · Dec 05, 2020 at 02:23 PM

Hi John

Thank you for your time and great feedback, what understood is the Tail current can be 2 different values,

By default it the MPPT is 2Ah and BMV 4 % can be left as its If no changes needed

your advise highly appreciate

ishtiaq

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Trina commented · Dec 05, 2020 at 05:10 PM

If you don't use your system much when in absorb or float mode the defauls will work fine!

Remember one (amps) is for the mppt to change charge states and is essemtially.more critical, while the other (on the bmv) is more for the correct SOC reading at any given.moment which you can more "harmlesly" play around with (volts) and can have some dramatic results depending on how and when you use and then read your system!

It would probably be easier if we had different tail terms!

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ishtiaq Trina commented · Dec 05, 2020 at 10:17 PM

thanks for clarifying, appreciate

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Answer 3 · 2020-12-05T16:59:13Z

Trina answered · Dec 05, 2020 at 04:59 PM

It depends on which one you want to get a reading from for your MPPT state charge change overs in expert battery profile mode vs.networked to the BMV and using it's setting for defining SOC via networking things where "tail current" is more for SOC and not as critical but csn be used here.

For insance you can.leave the mppt default for your battery type as is and play with the bmv settings to get the most accurate SOC reading at any given time depending on HOW you use your system (If I recall correctly). I had to edit mine to around 3% and 10 or 11 minute for the BMV to read SOC when I would charge something mid-day quickly when there was still plenty of solar energy. If I set it to 4% and a short time when it was networked to my mppt it would change charging stages in inacurate ways -because I was drawing a big load but for a shortime.

Generally you don't need to alter the defaults or go into "expert" charge profiles customization if you are asking about it here and don't understand it. Victron won't say that as they are being polite. *wink*

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