mppt vs pwm

CA Traveler wrote:

jrnymn7 wrote:
CA T... said,

"No need to use 13V as the controller will ramp up discharged batteries to 14.8V for bulk charging."

Depending on the C-rate, it could take hours to get to 14.8v. (Better safe, than sorry).

The unquoted part of what I posted was about the MS MPPT45 and it's derating at 45A as per the specs. At 45A it's not going to take hours to get to bulk charging.

Correct MS is better safe than sorry by protecting the controller against more than 45A output and over paneling.

Less quality controllers well.....

I was not zero-ing in on one particular controller, necessarily. Just using 13v as a realistic denominator for figuring out possible max amp output. I used it when showing the possible output of the eco-worthy, as well. It applies to sizing all mppt controllers, seeing as it's about Output Power vs. Vbatt.

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.

So, to safely size any mppt controller, one must consider Max Power and Min Vbatt (+R). In the Op's case, 544w / 13v = 42a, regardless of which controller he decides to go with. It so happens, the Morningstar 45 will work, but two eco-worthy 20's may not, in full sun. And going with 3 eco-w's creates more problems than it solves; not to mention little, if any, cost savings, when all is said and done.