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RVing message boards => Tech Talk => Solar => Topic started by: Frank B on May 09, 2017, 12:37:35 PM

Title: Best MPPT controller?
Post by: Frank B on May 09, 2017, 12:37:35 PM
OK, searched the forum, and the web, and there is little that factually differentiates one brand / model of MPPT controller from another.  It appears to be the 'the wild, wild west' with regard to solar, which is still very much in its infancy.

I started a thread here while on vacation a few months ago:,102402.0.html

I am now ready to buy and install, but have some questions on 'best MPPT controller' as well as best installation.

1) Is there a 'best controller' on the market, or are they all pretty much comparable?  Has anyone found a reputable and 'neutral' site that does REAL comparative performance testing of these units?

2) For larger PV arrays, are two smaller controllers better than 1 big one?  The smaller ones are cheaper. :)

3) Just how noisy are these units?  I would think that they must have step up and step down transformers in them to do their job, and they are likely high frequency (1 KHz or better).  Do they whine?  We don't have a 'basement' in our TT, so I may have to mount the controller(s) in the fridge cavity, or inside the coach on a wall.

I am looking to add 4 residential-style panels flat-mounted on the roof of our 30' Arctic Fox TT. The ones I have in mind are about 275 watts at 38 VOC (, so they will all be wired parallel to the controller(s).  As all roofs are slightly curved these days, two panels on one side may often be  angled slightly more toward the sun that the two on the other side.  Will having a separate controller for each side produce any measurable improvement as opposed to a single controller controlling all 4?

Thanks for any insight you can offer.

Title: Re: Best MPPT controller?
Post by: kdbgoat on May 09, 2017, 12:52:51 PM
Here's the best advice I can provide when it comes to solar on an RV:
Title: Re: Best MPPT controller?
Post by: Frank B on May 09, 2017, 02:06:53 PM
WOW!  Lots of information there!  Gonna take me a while to digest that, but I will read it.


Title: Re: Best MPPT controller?
Post by: kdbgoat on May 09, 2017, 02:37:14 PM
Handy Bob has a lot of griping in his blog, and he's not a fan of MPPT controllers, but he puts out a lot of good information. If nothing else, read the battery charging puzzle. The key to his systems working well is to use temperature compensation for charging, and use the battery manufacturers max voltage for the absorption phase of charging, and make sure your wiring is large enough to minimize voltage drop. Pack those batteries to the max voltage to get a true full charge so you can have the max amount of power available when needed.
That means whatever controller you decide on must be capable of being adjusted to the battery manufacturer's max recommended voltage, and be able to utilize a temperature monitor on the batteries. That will narrow down the field a bit for you.
Title: Re: Best MPPT controller?
Post by: Frank B on May 09, 2017, 03:18:20 PM
Thank you.

I am not a perfectionist in this area. 'Best' bang for the Buck' is what I am seeking. If I waste some solar energy, hey, sunshine is free.

In the quick glance that I was able to give the other link today, I see that my point of view is not out in left field. So, if there is a MAJOR difference between controllers, then fine, I want to know. If not, then I'll shop for the dollar value. That is why I plan to use residential PV panels. It is also why I am looking at multiple cheap controllers vs one honkin' big expensive one.

Will probably take me the rest of the week to read through the first link.

Thanks again!
Title: Re: Best MPPT controller?
Post by: Gizmo on May 09, 2017, 03:50:08 PM
Morningstar Trimetric controllers are hard to beat.  They are well made and perform flawlessly.  Outback and Blue Sky also make very good units, but if I recall correctly they are more expensive, yet as well as the Trimetric's perform, I would have a hard time justifying the higher cost.
Title: Re: Best MPPT controller?
Post by: Sun2Retire on May 09, 2017, 05:56:29 PM
Morningstar Trimetric controllers are hard to beat.

X2. Happy with ours so far
Title: Re: Best MPPT controller?
Post by: svrapture on May 09, 2017, 08:46:20 PM

X2. Happy with ours so far

X3 - could not possibly be happier with both of mine.
Title: Re: Best MPPT controller?
Post by: prfcdoc on May 09, 2017, 09:06:20 PM
X4 - I've had mine for 3 years and it's been flawless.
Title: Re: Best MPPT controller?
Post by: Kevin Means on May 12, 2017, 03:04:00 PM
The man Kdbgoat mentioned (Handybob) worked with me on the installation of our system, and I agree, he's a very knowledgeable guy when it comes to RV solar. His name is Bob Shearer and he lives off-grid in Montana (He's quite a personality.) For a small stipend, he helped me choose and install a system for our RV that was specifically designed around our goals, usage, environment and storage capacity. That included our 80 amp Outback FM-80 MPPT controller. I will admit, however, that Bob would have preferred that I bought a Morningstar or Blue Sky controller, but he admits that it's because he doesn't like one of the guys who owns Outback. Oh well  :) In my opinion, unless your solar panels will be divided in purpose, or have unusually high output, there's no need to use separate controllers.

Morningstar has a good name. I probably would have bought one had they made an 80 amp controller, but three years ago they didn't. They only went up to 60 amps. I don't know if that's changed or not. Our Outback FM-80 is programmable for different types of batteries and has performed flawlessly with our AGMs. It has its own internal cooling system, which comes on all the time. The controller is mounted in a basement compartment about three feet from the batteries. When you're outside, you can hear the cooling fan kicking on and off, but I wouldn't call it annoying. It's like a computer fan.

The panels you mentioned are physically pretty large (65" X 39") so you might want to double-check your measurements to ensure that, once they're on your roof, they're not shaded by vents, AC shrouds etc. And remember, solar panels are exposed to frequent and occasionally strong gust loads while driving down the freeway. Only time will tell how well the solar cells themselves will hold up while flexing under those loads. The cells on larger panels will flex more than those on smaller panels.

Several panel manufacturers make solar panels with similar output ratings as the CSK 275Ms, yet they're much smaller and lighter. That's because they were designed for off-grid use vs. grid-tie use. For example, a Grape GS-S-160-Fab8 160 watt panel has, essentially, the same amp output rating as the CSK 275M (8.65 amps vs. 8.8 amps for the latter) yet the Grape panel is 7 inches shorter and a whopping 13 inches thinner than the 275M - and it weighs just a little more than half as much. That's pretty significant - especially when you're getting the same amp output performance out of them. When it comes to RV solar, it's all about replenishing amps, not voltage. Just food for thought as you move forward with your solar project.