SmartSolar MPPT 75/15 with AGM strange battery behaviour

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jevil asked Jul 4, '21

SmartSolar MPPT 75/15 with AGM strange battery behaviour

Hi.

Yesterday, on a sunny day, I plugged the stuff for my caravan together: 100W solar panel, SmartSolar 75/15 and a 120Ah AGM. Made all the settings as stated on the battery (U_Absorption 14.7V, U_float 13.7) and it works fine - at first. It started bulk with all the current the panel was able to deliver at that time (~ 5A). The load output was at 0.1A. Some hours later it arrives at Absorption at 14.7 - okay so far.

Now the strange thing: When I was back also some hours later, the charger was at bulk loading again with ~5A and the battery voltage was slowly decreasing (~ 0.25V / hr) - I stopped the process as the terminal voltage reached 14V. Battery was cold. Does anybody have an idea what is happening here?

Best regards, Jens

MPPT SmartSolar AGM Battery

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Answer 1 · 2021-07-04T06:39:12Z

Paul B answered · Jul 04, 2021 at 06:39 AM

Jens it likley that the solar was having less output and thus the voltage was decreasing, even though it was in bulk, there are lost of reasons why the above is just one.

or something elso had turned on and power was being used

suspect that you have nothing to worry about

there are lots of reasons why the above is just two reasons.

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Answer 2 · 2021-07-04T07:47:20Z

jevil answered · Jul 04, 2021 at 07:47 AM

No, I can definitely say that there was no more load which could have discharged the battery in between. And sun was shining all time. Imho it must have to do something with battery chemistry or something like that. I am an power electronics engineer, but batteries normally are not my field of scope.

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Paul B commented · Jul 04, 2021 at 07:57 AM

the batteries being AGM will always take some amps there siting voltage is around 12.7 volts when full, , Lithium phosphate are some much better

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jevil Paul B commented · Jul 04, 2021 at 08:58 AM

5A for float charging a 120Ah battery - never ever. And - as I already wrote - the charger went back to bulk, not float. Also the current at absorption had already dropped to less than 2A before.

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Answer 3 · 2021-07-07T20:06:41Z

jevil answered · Jul 07, 2021 at 08:06 PM

Does nobody have an idea what could be going on here?

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