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Old 03-13-2022, 04:03 PM   #1
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MPPT solar charge controller with 12v panels...

I wanted to share an MPPT observation (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.irv2.com/forums/f56/proj...er-529010.html)



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
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Old 03-13-2022, 04:28 PM   #2
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I don't see where you are getting any gain. Panel voltage x current is 175 watts, charging voltage x current is 168 watts.

It isn't a true comparison of MPPT to PWM without also looking at PWM output.

You would probably better take advantage of MPPT by putting panels in series.
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Old 03-13-2022, 04:34 PM   #3
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Quote:
Originally Posted by John Hilley View Post
I don't see where you are getting any gain. Panel voltage x current is 175 watts, charging voltage x current is 168 watts.

I believe if the PWM solar charge controller was used, it would drop the voltage down from 18.5 to 14v to the batteries (in this example) and the current going to the batteries would equal the current coming from the panels which in this example was 9.5amps (instead of 12amps when using the MPPT charge controller).


With the MPPT charge controller, I'm getting 14v and 12amps to the batteries.
With the PWM charge controller, I would be getting 14v and 9.5amps to the batteries.


At least that's how I understand it. Others can feel free to correct if I've got something wrong.



-Chris
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Old 03-13-2022, 05:11 PM   #4
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I found about the same gain switching from PWM to MPPT controllers. Of course I also changed my panel wiring from parallel to two pairs in series. This also led to my panels starting to put a charge in the batteries earlier and later in the day. Not a lot more, but anything helps.
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Old 03-13-2022, 05:34 PM   #5
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A pulse width modulating controller ( PWM )
allows up to its set point of voltage thru to the batteries.

If the voltage is higher then that, the controller starts modulating ( switching the power on and off ) to keep it steady.

Any volts from the panels above the set point are left behind.
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Old 03-13-2022, 07:46 PM   #6
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Quote:
Originally Posted by SJ-Chris View Post
I wanted to share an MPPT observation (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.irv2.com/forums/f56/proj...er-529010.html)



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

24hr solar charge test:
March 12th. Bay Area, California.
Sunny day with very few clouds. Sun never directly overhead.
Started with the batteries at 98AH as read from the battery monitor (out of 210AH total).
Everything electrical "off" in the RV, except the inverter (0.25amp standby).

Turned on the system (breaker/fuse from the panels) at 11am.
24hrs later, the battery monitor read 171AH.
73AH added to the batteries in 24hrs. I should have actually had the inverter off if I wanted to see the true solar total amount. At 0.25amp standby drain from the inverter, over a 24hr period that would be 6AH. So I guess the solar panels actually generated 79AH to the batteries.
79AH/3 = 26.3AH per 100w panel in 24hrs. Seems reasonable for this time of year.

Looking forward to trying it out while camping.

Happy Camping!
Chris
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