marekp avatar image
marekp asked

MPPT turns off when battery is switched to absorbtion.

MPPT turns off for 20 minutes when battery switches to absorbtion.

What is the reason for that?



DC power can be sent to grid because DC feeding is allowed.

When I reboot GX, MPPT production resumes earlier that if I do nothing.

mppt state
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2 Answers
Trevor Bird avatar image
Trevor Bird answered ·

Hello @MarekP ....your batteries don't switch to absorption, your VE.Bus charger switches to absorption. When that happens the terminal voltage of the batteries increases and the charging voltage of the MPPT solar charger no longer is sufficiently higher than the battery terminal voltage for any current to flow. Hence the current drops to zero. Within 20 minutes the Maximum Power Point Tracking algorithm re-evaluates the best voltage and current point to charge the batteries and when it resets starts charging the batteries again. When you reboot Gx it starts the MPPT evaluation immediately and gets their faster for that reason.

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marekp avatar image marekp commented ·

@Trevor Bird

It could be the case but MPPT solar charger is under "external control". Is it still doing this evaluation when under external control?


The PV voltage is way higher than battery voltage so there should not be a problem with too low voltage.

Charging voltage is rising slowly and MPPT solar charger is following voltage demand. Only when absorption stage kicks in both MPPTs are switching slowly OFF. There is no sudden voltage increase at point of switching to absorption.

I do not think MPPT needs 20 minutes to reevaluate anything.

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Trevor Bird avatar image Trevor Bird marekp commented ·

@MarekP ...External control provides basic instruction to the controller. It doesnt control the MPPT tracking. It doesn't take 20 minutes to evalauate the MPPT point. It normally takes about 30 seconds to evaluate that tracking point and that normally happens every 10 minutes. I canot explain why it is taking 20 minutes and not 10 minutes and can only assume it is becasue it si under external control. When you say gradually change, it is hard to know that given the default update interval for VRM unless you have changed that.

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marekp avatar image marekp Trevor Bird commented ·

@Trevor Bird

But there is no reason for MPPT tracker to loose control.

Battery voltage is the same before and after the point of changing from bulk to absorption.

Also two different and separate MPPT behave the same.

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billknny avatar image
billknny answered ·

What kind of batteries? What I see looks like normal behavior for Lithium batteries.

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marekp avatar image marekp commented ·



What is this "normal" that you see?

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billknny avatar image billknny marekp commented ·
LFP batteries do not have a long protracted absorption cycle.

From what I see in your graphs, the solar chargers drive the voltage up to the absorption setting, and the voltage stays there. Since no additional current is needed to maintain the voltage, the controller stops supplying any. If the controller pushed more current into the batteries, the voltage would continue to rise, and that would be bad.

Basically, the controller stops pushing current because your batteries are full, or so close to that they can not be safely charged any further.

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marekp avatar image marekp billknny commented ·

Thank you for your input.

My absorption cycle is set to 1 hour.

I have 2 MPPT chargers, 1 Fronius and 4 MP-IIs.

All charge the same battery.

Fronius is set to feed the grid and both MPPT chargers are also set to feed the grid.

If there is no need for MPPT chargers to charge battery their energy should be fed to grid.

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