Voltage of my Panels at maximum Amps is 19.1 VDC. And Voltage stays near this level whenever they are putting out a significant, useful level of Amps through the entire daytime. Thus, with a cheap PWM, my '200 watts' really works, at the best possible moment in "Bulk" charging, with no wiring losses , at about 200 * 14.4 / 19.1 (more like 150W). In the "Real World", I'm seeing only about 135 average for a "perfect" cycle of Bulk + PWM charging.
Why not a 3rd panel?
There is no question that I would get more energy into the battery, at slightly over half the cost of a decent MPPT, by simply adding a third "100 watt" panel to the roof (staying with the current "PWM", or upgrading to a somewhat better one.) But there is a problem with that idea:
Having tuned my torsion bars for "adequate" lifting power against the two panels I already have, (while not making it too hard to collapse the shell and clip into the brackets), there is substantial resistance for getting it started when collapsing- the sideways motion back to the Trailer Body, before gravity becomes "my friend" and helps to take it down the rest of the way. I feel that an increase in lifting power, to handle the increase shell weight of a 3rd panel, will create a significant increase in resistance at the beginning of the motion - my sideways push against torsion bar resistance on the way down. It's already quite an "mmmph!" to start pushing sideways, into an area where gravity helps to take it down the rest of the way.
So, Spend almost 2x more on a decent (== "high end") MPPT controller?
Aside from adding a bit more charge capability (maybe 1/2 as much as 3rd panel used inefficiently) a good one would appear to have other have benefits for my use of the battery bank:
- In camp on sunny days, achieving 90 - 100% battery SOC (instead of 80%-85% with my stupid PWM). Its got a high quality temp sensor, where my PWM has none at all.
- Anti-Sulfation per my specification instead of the bad PWM logic.
- Accurate readings for Battery and Solar charge Amps and Volts, instead of nearly-always-green "idiot lights".
No reading of power being delivered
from the battery, in the setup which I'm considering.
Right now, my battery gets to about 80% SOC during a sunny day with the PWM. That gives me about 30% of the 'nominal' total battery capacity (before reaching a red-line value of 50% SOC.) With a really smart controller, completely aside from the fact that it's creating MPPT levels of current to begin with, I think that I could get about 1/3 more useful SOC into the batteries.
Since it can probably double the lifespan of my batteries (which I
have been using down to less than 50% SOC, on occasion) by reaching a much higher max SOC during the charging day (without a lot of "playing around") there's probably a payback in one set fewer batteries to buy over the next 1012 years. Between the battery lifespan improvement, the improvement in usable capacity (with no additional batteries, cabling, or weight), push-button Anti-Sulfation, and decent logic to switch back from "Float" into MPPT "Bulk" or "Absorb" operation, I'm seriously considering that acquisition for reasons which seem defensible. Completely aside from getting a really "kewl upgrade".
Mounting in the 2619 would be a bit awkward - the cheap PWM sits outside, but the expensive MPPT would need to be inside (Maybe along the "front" wall of the fixed-size Trailer Box, next to the collapsing dinette.)
- - - - -
Done. Rogue model "2024", now discontinued, bought from remaining inventory and installed 5/2015.