Lifepo4 ( not victron and bms builtin) problem chargin with mppt 150/70

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ulysse asked Apr 3, '19

Lifepo4 ( not victron and bms builtin) problem chargin with mppt 150/70

Hi,

I have 2 x 300ah lifepo4 // mode ( bms buit in) with mppt 150/70 connected to 2 x 335w solar panels . Mppt is setup to default Lifepo4 . The strange thing is i know the SOc is around 50%. In starting day the mppt is in Bulk mode, very quickly it’s moving to Absorbtion ( around 2 hours ) and 1 hour after it’s mouving to float...so i never reach 80% ( the goal) or 100% . I have to disconnect panel then the cycle start again. I’m in a very sunny country where i can charging 40a/h during 5 hours ( so 200ah expected), What’s wrong ?

battery charging

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ulysse commented · Apr 03, 2019 at 07:32 AM

i have notice voltage never reach 14,2 or 14,4..bulk to absorbsion and to float moving always before 13,6 v ( tested with handle tester and confirmed by my battery manager).

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Answer 1 · 2019-04-04T04:34:39Z

mvader (Victron Energy) answered · Apr 04, 2019 at 04:34 AM

Hi; we’ll soon have a firmware update that allows to set a fixed Absorption time on your MPPT; rather then the adaptive method that its using now.

That will fix your issue.

A few more weeks, is what I expect.

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Mark ♦♦ commented · Apr 04, 2019 at 05:38 AM

Hi @mvader,

Will the option of retaining the 'adaptive absorption time' also be enhanced with the ability for users/installers to configure the adaptive parameters?

(Such as the voltage limits for each band & the % of max time for each band)

Personally the current adaptive absorption time works very well for me, but it would be nice to slightly 'tweak' the parameters.

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mvader (Victron Energy) ♦♦ Mark ♦♦ commented · Apr 04, 2019 at 06:19 AM

Hi Mark, no. Not now at least.

But what is coming is to have a BMV send over the battery current. Either via a Venus GX device or via VE.Smart networking for a smaller system. Advantage being that you can then make it stop charging when the battery is full (accepted charge current <= x).

Applies for lead batteries only. Most, if not all lithiums, are better off using fixed absorption.

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Mark ♦♦ mvader (Victron Energy) ♦♦ commented · Apr 04, 2019 at 10:00 AM

Yes I heard/saw that ending absorption phase based on BMV charge current was in the works & also saw the related task on GitHub the other day.

This will really be a great enhancement & provide a far more accurate/well controlled charge cycle - so it's an update I am very much looking forward to!

(PS. My battery bank is VRLA AGM)

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holle Mark ♦♦ commented · Apr 04, 2019 at 07:31 PM

Hi Mark.

Will this feature of configurable absorption time be available for solar chargers MPPT with Bluetooth?? Do I understand right that this new feature will be based on measurement of current instead of voltage??

Best, Holger

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Mark ♦♦ holle commented · Apr 04, 2019 at 08:51 PM

Hi Holger,

I beleive that there are 2 new features coming;

1- Optional FIXED absorprion time (rather than adaptive only)

2- Absorption end based on charge current only. With this upcoming feature mvader stated above that communication can be via VE.Smart Network (Bluetooth).

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holle Mark ♦♦ commented · Apr 08, 2019 at 11:46 AM

Hi Mark.

Just a general question for my understanding: How does MPPT 100/30 measure the battery's voltage? By reading from the battery cable or is there an internal algorithm? Actually I've measured a difference of 0,3 V between Battery (13.5V) and MPPT (13.8).

Thanks for clarification.

Holger

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Answer 2 · 2019-04-04T05:25:22Z

wkirby answered · Apr 04, 2019 at 05:25 AM

The question I have is why it moving out of Bulk early. The firmware update will not solve that particular problem.

Do you have good cables between MPPT and battery? Voltage drop on those cables will cause the MPPT to read a higher Voltage than what is actually at the battery terminals, especially when you have good sunshine and high charge current,

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ulysse commented · Apr 04, 2019 at 07:53 AM

Cable 16mm2 1m distance between batteries and mppt. Working fine before i change Get for Lifepo4.

For Firmware, i have to buy bluetooth extention. Is it possible to do it without bluetooth ?

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Answer 3 · 2019-04-04T21:46:23Z

offgridsa answered · Apr 04, 2019 at 09:46 PM

This is great news.

Having the ability to trigger the Absorption to float transition based on a true battery charge current value that takes live loads on the battery into account in the calculations.

Combined the above with a fixed absorption time.

For example, 40 min absorption or 8A charge current (what ever parameter is seen first will trigger float)

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