150V 45A MPPT - roll your own

Author	Message
rogerdw Guru Joined: 22/10/2019 Location: Australia Posts: 877	Posted: 11:37pm 15 Feb 2024         poida said   the idea is that at some time, BV will get to the absorb setting. this means it will no longer care about MPPT and just maintain the battery at absorb voltage. this is because there is more than enough solar to keep the battery at absorb voltage. Yep okay thanks. It was the dropping back to MPPT which was worrying me, which you've explained below.   Quote   And when it first gets to absorb voltage it starts a timer. The timer sets how long to have battery at absorb voltage. Yes, understood.   Quote   the timer will count down while BV > (absorb voltage - absorb_tolerance) this is to allow for inverter transient loads and minor clouds and such. No point in bailing out of absorb mode just because a fridge switched on, dragging BV down 3 volts. I think this is what I was missing. I had no idea how much varying loads on the inverter  ...  and outside weather conditions would effect the levels and so quickly. I understand the theory okay (I think) but this is my first real solar system, so still more to learn.   Quote   There is an absorb time setting. This has to be achieved before float mode will be enabled. Yep, understood.   Quote   so, lets say float mode is finally enabled. Again, BV needs to stay above (float - float_tolerance) to remain in float mode. if BV is less than (float voltage - float_tolerance) then it goes back to MPPT mode and it's likely to quickly then go to absorb mode. Okay, so this is what I've seen a few times. So if this happens, from Float back to MPPT  ...  then on to Absorb again  ...  does the Absorb Timer start from the beginning again? I think I might lower my Absorb setting a smidgeon, and perhaps widen the tolerance just a bit as well. At least I understand what I'm looking at better now. Thanks very much Peter.