MPPT 75/15: Loss of 70% upon ugrade to 1.64?

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minthral asked 10 hours ago

MPPT 75/15: Loss of 70% upon ugrade to 1.64?

After having upgraded to 1.64, I only get about 30% of the energy I used to get before the update. This is not sufficient to fully charge my camper van's battery on a blue sky summer day in central Europe while the fridge is running. This used to work well BEFORE the upgrade of the firmware.

The Solar Voltage starts at around 40 V in the morning and then gets controlled down to around 30V and then gets controlled down to around 20 or less Vs. the pattern happens every day - so no, this is not caused by shading nor by faulty connectors (I checked all of them) nor by dirt, dust or bird drippings.

Also, it seems to me that the charger actually tries to find the optimal charging point and for some reason decides that this were at 30 %.

I have two 120W panel in serial configuration on my roof. So that adds up to 240 W and twice the voltage.

This configuration has served me very well for three seasons but os now borderline after the firmware upgrade.

Would anybody have hints to how the nominal power supply of up to 200 W can be restored? Getting 67W@5A is just not good enough.

Thank you in advance.

MPPT SmartSolar

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niklas-schauberg commented · 5 hours ago

hi, regarding PV-voltage: it says nothing about the solar radiance. it says only that there is any light on the panels. if you look at an example from my MPPT yesterday you can see that voltage is more or less “on or off“ while current reflects the production.

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minthral answered · 3 hours ago

Hi @Niklas Schauberg

Thanks for your responses. The drop in voltage actually puzzles me because, me too, I would expect it to stay around the same value once there is light shining on the panels with only the current varying during the day.

Can the MPPT charger even control the input voltage to such a degree?

I am using an AGM battery with the recommended settings for the absorption and float voltages (14.8 and 13.7 V respectively).

I have watched the system operate over the years but I never did take screenshots. I remember not having noticed a drop in voltage as I observe it now.

On a day such as today, with a clear blue sky and the roof of the van tilted towards the sun, I would have expected the battery current to go up to close to 15A with the battery voltage I observed at noon (which would be about 200W). Yet production seems to have been capped at (strangely) precisely a third of the previous capacity and the active cooling of the controller with a fan would not have been required (I added the fan three years ago because I noticed that the device got hot at full production rate). The settings say that max battery current is 15A - not 5A as observed.

My impression (based on past observations) is that the solar voltage is the limiting factor (i.e. once production starts, it drops twice by a third - for unknown reasons) when the solar current is within the usual range.

Any idea what could cause this?

Can it be the charger or is this some weird coincidence where something else broke at the time of the update?

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Answer 1 · 2024-07-27T08:04:48Z

minthral answered · 10 hours ago

The daily voltage graph. What causes the two step downs and reduction of power?

15 hours of bulk charge on a BLUE summer day without reaching the cut off voltage of the battery.

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Answer 2 · 2024-07-27T08:29:24Z

minthral answered · 10 hours ago

It almost looks as if the charger tried to increase the voltage every now and then but then measures a drop in current.

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Answer 3 · 2024-07-27T08:39:20Z

minthral answered · 9 hours ago

Before the upgrade to 1.64, the voltage would go up in the morning and stay up during the day yielding up to 198 W. Now with the reduction to about a third in voltage, the yield seems to max out at 67 W at about 5A (on the battery side).

To me this indeed looks like a faulty power tracking algorithm in the product that finds a local optimum and never leaves it.

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Answer 4 · 2024-07-27T08:48:47Z

minthral answered · 9 hours ago

The big question: what could be causing this?

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niklas-schauberg commented · 5 hours ago

hi, this is absolutely normal and is called MPPT, the system is searching the sweet spot of your panel‘s production.

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Answer 5 · 2024-07-27T13:03:50Z

niklas-schauberg answered · 5 hours ago

please be so kind and post some pictures how it looked before and how it looks after the update.

please consider also that simply a full battery can cause lower yield.

what kind of battery do you use?

how are and how were your voltage settings before?

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Answer 6 · 2024-07-27T14:55:25Z

minthral answered · 3 hours ago

Daily curve BEFORE the issue developped. Note that the van was parked on the west side of a building and remained in the shade until noon.

Another daily curve BEFORE the issue developped. Note that absorption voltage was reached in the morning on this day.

In both cases, the voltage was around 40V as long as there was light.

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