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xaver60 asked

after two years of use, MPPT 75/15 switches to OFF-mode even in bright suns shine and does not start loading again

I am using a MPPT75/15 and a solar panel Wattstunde 120SPS (Voc 21,8V ISC 6,8A) to load the LiFePo battery of my camper. For the last two years everything worked well.

During the last trip the system stopped working in bright sunshine. The MPPT was switched off without any known reason and did not resume working. Sometimes this lasts one day, or even several days.

Firmware reset and disconnecting / reconnect both battery and solar panel did not solve the problem.

I checked all connections as well as the panel which delivers around 22V (open circuit) and 2 to 3A short current.

Yesterday I could record the strange behaviour (see attached screenshot). The MPPT starts to load the battery in the morning. During the day it reaches float voltage. In this state the loading current was reduced to nearly zero. But after some time the MPPT swithes off and shows a solar voltage equivalent to the battery voltage. Because I need some light to work in the car the battery was discharged. The voltage drops below bulk voltage (13,5V) minus bulk offset (0,1V) but the system does not start loading again. I disconnected the solar panel to measure the electrical values which have been ok. This time the MPPT starts working again after reconnecting. As described above the MPPT stays in Off-mode after reconnect.


May be this is a software problem?

Are there any suggestions how to sort out the problem?

mppt state
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klim8skeptic avatar image klim8skeptic ♦ commented ·
Your trends graph would be more interesting if it had run the full day.
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