MPPT solar charge controller with 12v panels...

[SJ-Chris]

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

[CA_Traveler]

Check your controller for maximum limits. My controller can be over paneled in watts because it will restrict the output amps to the max. I cannot add another serial panel due to the max input voltage. So instead of 3x serial I would have to use 2x2 parallel serial.

[CA_Traveler]

The controller input voltage maximum MUST be greater than the panel Voc or the controller can be damaged. This is especially important for SERIAL connected panels. The difference should include the voltage change due to the temperature compensation factor.

On a sunny day Voc can be caused by "cloud edge effect" and other transistional shade conditions like driving.

Updated At 0F each of my panels Voc will increase 5V or 15V total for 3 panels.

[CA_Traveler]

Lwiddis wrote:
I lose a BUNCH more than 25% at 122F! That’s just about too hot for me. lol

Definitely panel temperature which can be even higher.

[afidel]

Lwiddis wrote:
I lose a BUNCH more than 25% at 122F! That’s just about too hot for me. lol

Pretty sure that's panel temp not ambient!

[SJ-Chris]

That is a good question. Strangely, I didn't even think about connecting them in series. I connected them in parallel. I can appreciate how in series they would collectively get to say 14v+ earlier in the day and stay at 14v+ later in the evening. That would generate a little extra charging. Does anyone have any real life data on how much/little gain this ends up being in the real world? Would be interesting to know. Since all the panels are connected on the roof it wouldn't be terribly hard to re-wire them in series.

I guess the gain comes from the time between when the individual panels are producing ~5v to the time they are producing ~14v (and the reverse as the sun goes down). I'm curious....is this ~10 minutes in the morning and ~10 minutes in the evening? 20 minutes on each end?? Anyone know?

I suppose when I go boondocking next if I'm up before the sun I can keep an eye on my solar charge controller and measure the time...

PS: Solar is addictive.

Happy camping!
Chris

[StirCrazy]

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..

[Lwiddis]

I lose a BUNCH more than 25% at 122F! That’s just about too hot for me. lol

[SJ-Chris]

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

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

[CA_Traveler]

Interesting results - There have been numerous past posts on this subject and 25% might be high. But the technology certainly has improved. Another factor is higher summer panel temperatue which decreases panel watts. My 250W panels have 25W less at 122F. Your numbers indicate about 175W from the panels which is in the ballpark for flat panels and lower elevation sun.

[Lwiddis]

An MPPT is very helpful to those without roof space for panels.