mppt vs pwm

smkettner wrote:

jrnymn7 wrote:
Putting 45a into a 215Ah bank, it will remain in bulk until ~80% soc. A 50-80% would take about an hour and a half; voltage slowly rising from about 13v to 14.8v over that time period. Putting 45a into a 430Ah bank, it would remain in bulk until well past 80% soc, voltage slowly rising all the while. The only way to get to 14.8v rather quickly would be to use a very high C-rate, like 75a on a 215Ah bank.

You assume you get 45 amps at daybreak... you don't. Amps ramp up slowly with the sun and often can be at 14.8 before max output is even available.

To really get max, the battery needs to be a bit oversize or you need cloud cover to about 11am. Then with sudden clearing and full sun you will get max power into a low battery.

Hard pressed sometimes to even get down to 50% because each day you are closer to 95% to 98%+. So the 50-80 becomes 68-98 and you hit that 80% fairly quick.

I'm not assuming anything, but rather planning for a worse case scenario. As you pointed out, if charging didn't begin until near noon, AND if that was following a couple of bad days, resulting in a deeply discharged bank, then yes, a 50% cycle is quite possible.

Nevertheless, even a 70-80% on a 430Ah bank would take an hour, using 45 amps; voltage starting out somewhere between 13 and 14.8v, and ending still short of the setpoint. So I fail to see how 14.8v can be considered relevant for sizing.