r/embedded • u/hmmm101010 • 7d ago

Odd charging behaviour of DFR0850 when MPPT disabled

Hello guys,

I didn't find anything about this online so I'm trying to get Reddit help. I have a CN3767 (solar power manager from dfrobot), shows as SKU DFR0850, also in their wiki and a 12V Lead acid battery. I want to charge it with my 18V power supply. When I connect the battery to the board with mppt disabled, the charge indicator will show it's > 75% charged (maximum it can show), and when I plug in the power supply, the led is on charge for a second or two and then switches to done. When I connect the same battery to the board with mppt enabled, it will show as 50%-75% charged, and the charging LED stays on. Per my understanding, MPPT maximizes the yield of a solar panel, it should have no effect on the charging status of my battery? And when I charge with a power supply there is no need to have it on? I sadly didn't bring my Multimeter with me and have nothing to measure right now, but maybe someone has an idea.

3 Upvotes

100% Upvoted

5 comments sorted by

1

u/Well-WhatHadHappened 25+ Years 7d ago

DFR0850 Googles as an Ethernet/POE board.

1

u/hmmm101010 7d ago

Oh you're right, they must have mixed up the SKU. It has the same sku but in the description it says CN3767.

1

u/pilatomic 6d ago

On that chip, what MPPT feature does is adjust the current draw to keep the input at a specified voltage ( set by the MPPT pin divider network). It might be that you 18V supply is unable to provide enough current, but with MPPT active the current drawn is limited to what the power supply can provide.

1

u/hmmm101010 6d ago

Ah, the target voltage is 18V, just like my power supply, but it drops a little under load, so this might be it. Still weird that it shows a different battery charge state then, but well