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mauam avatar image
mauam asked

10Ah AGM equalization MPPT75/15

Hey everyone

For a small off grid project (IR movement sensor and a connected 10W led light) I bought a 120W PV Panel and the MPPT 75/15 Controller. Those are connected with a 4Ah WET Lead Acid or a 10Ah AGM Battery.

Seems overkill I assume :-) But the thing is, the place for the PV panel is far from optimal. Direct sunlight for only 3 hours max.

I did some Tests today and I observe things I do not fully understand.

The Battery (yt12b-bs) I took from my motocycle was not charged since October 2020 and was quite low (11.78V). The Battery says normal charging at 1A, fast charging at 5A. I therefore kept the basic settings of 5A on the controller and started the process.

After a short time the controller switched from Bulk to Absorbtion later to float. After I disconnected the battery and gave it some time I could watch the voltage drop way below 12.7V.

I played with the settings and first of all set a max current of 1A. Now it spent way more time in Bulk state, eventually changed to Absorbtion and later to Float.

Once again disconnecting the Battery I still saw it fall back lower than 12.7V.

I read a bit about the equalisation mode and thought I'd give it a try. The settings on the controller are still at default (16.2V EQ Voltage) I put everything together and watched the controller.

I'm confused as the Voltage sent to the Battery never reached 16.2V It was stuck at the Absorbtion Voltage of 14.4V I then set the Absorption Voltage to 14.6V and saw the Voltage rise to exactly 14.6V (low amperage of 100mA in Eq mode)

My first question is: Am I wrong expecting to see a equalization Voltage to reach the configured 16.2V? Did I get the Idea wrong?

Secondly: The Voltage on Battery was constantly falling until it hit 12.35V where it stays right now.
Do you think this block is still usable? Oder might it be over with this one?


Thanks in advance

Best Regards

MPPT ControllersAGM Batteryequalisation
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3 Answers
Paul B avatar image
Paul B answered ·

AGM batteries should not be equalized.


if the voltage of the battery falls to 12.7 this is ok

but if it continues to fall even when not connected to the load . then the battery is at end of life I suspect.


however keep in mind that a 10 watt draw is about 0.8 amps so it can quickly flatten a 4A/H battery ie around 5 hrs for 100% flat

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mauam avatar image
mauam answered ·

Hi Paul an thank you for your Answer

After disconnecting the Battery there is also no load connected. It was just sitting here.
I charged it this morning again. It was almost only on float. I took it of and let it rest for 4hours. It no has a voltage of 12.4V

Once the system is in place it should only run fot probably 2 hours a night. It should just kick in and run when someone walks by the bicycle stand to lock or unlock his/her bike.

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mauam avatar image
mauam answered ·

I got a used 80Ah Car battery which is still in good shape. Next to having enough Power it will also work as an anchor for the panel if its getting windy.

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