MPPT75/10 reluctant to start?

I have an old mppt 75/10 which won't start if you connect the battery and then the solar power.. The remote data shows correct values for the PV voltage, battery voltage is reading about 1v high. If you connect the solar voltage (~26V) and a load of about 4W to the load terminals, and wait a few seconds, the MPPT starts and the load turns on. At this point you can connect the battery, and it will charge. I'm currently waiting to see if it will maintain the float voltage. Unit has also been updated to latest firmware V1.59.

I'm wondering if the error in reading the battery voltage is related to the starting problem. If you use Victron connect to turn off the MPPT function, then back on, it also fails to restart, and you have to disconnect the battery again..

update: The unit did not restart after abs to float transition with 14.4 / 13.6V change. Now trying with much smaller change

updatre2: It seems to have worked with bulk = 14.21 and float = 14.2. With these so close together, I guess the converter never stops during the transition, however once the tail current drops below ~ 0.6A it all stops again and mode goes back into bulk.

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Mike Dorsett commented · Jan 25, 2023 at 08:07 PM

After some time, the unit appeard to start working properly, but only for a few days. When I tried to restart the unit, I found that the charge current limit was inoperative. As I'm trying to use this for a dc/dc step down, this limit is important to prevent overheating and is set to 5A. However, I measured the output current at 12A!!. This has caused a melt down in the switching circuit. so there would appear to be a processor fault - despite the firmware update working ok, and the ADC's mostly reporting reasonable values...

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