SJ-Chris wrote:
I wanted to share an MPPT observation/experience (some of you likely are already aware, but many others maybe not...)
I just completed my 3rd solar install on my 3rd RV. (I enjoy these projects, and have been becoming a bit of a solar nerd...and mostly I hate dead batteries!) These are fairly simply installs (the first 2 were 500w with a 2000w inverter on one and a 1000w inverter on the other). They used commercial 250w used panels ($35 each) and an MPPT controller. Doing great for the last year (https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30217540/srt/pa/pging/1/page/1.cfm)
For this latest project, my 23' Class C RV has just two new 6v GC batteries (210AH) which is all I really want/need in there. A while back I acquired via craigslist three 100w used 12v panels (tested prior to purchase) for $25 each. I had a cheap PWM charge controller I was thinking of using. But I decided instead to buy a MPPT controller to use. I'm glad that I did. Even though the solar panels are "12v", they actually produce at 18-21v as you are probably aware. So the MPPT charge controller actually converts that extra voltage into extra charging current.
This system is 300w flat mounted on the roof. After I completed my install, I did a test. I discharged my batteries to about 50% and then I turned on my solar (toggle fuse) yesterday morning. I can see on the charge controller display, for example, that the panels were at 18.5v and the current coming in from the 300w of panels was 9.5amps at 11am. The display then shows the voltage going out to the batteries (ie. 14v) and the amps going to the batteries at 12amps. (Note: Those numbers might be off by just a bit, I'm trying to illustrate a general point.) That translates to roughly 25% MORE charging to the batteries than if I was using a PWM controller.
So I guess that means my 300w MPPT system is actually equivalent to a 375w PWM system had I gone that route.
Just something to think about if you are installing "12v" panels.
(Side note: I actually bought a 4th 100w 12v panel at that time, and I used the cheap PWM controller and 25' of wire and a fuse as a portable system. Currently used to keep my boat batteries charged during storage but in theory could come with me on an extended boondocking trip if I ever thought I needed an extra 100w of portable solar. Handy to have :) )
Happy Camping!
Chris
Two 2015 Thor Majestic 28a Class C RVs
One 2013 Coachman Leprechaun 210QB Class C RV
did you put them in series or parallel? if you switch it to series with all three panels you will see even better early morning, lait night, and cloudy day charging. as long as your controler will handle 300 watts in series. some times it isnt worth the work to rewire them depending on the layout though..
