Newbie to solar question

I jumped into solar as a newbie. I went with two 140 watt 12 V nominal panels (great price on sale) and I wanted to have the potential to upgrade without having to rewire/reinstall anything new if that happened. My tt still just has the 2 oem group 24s (140 Ah) and I know that will be a priority future upgrade. Since I would start with around 15 A max current and wanted to plan for up to double that, I started looking for 30-45 A rated PWM controllers. At the price ranges I was finding, it seemed like it was less than $50 more for a "nice" Morningstar Tristar. I've been very happy with that controller, it has the ability to be fully programmable and has many options like diversion load ability. Maybe more capabilities than I will ever use, but I feel good knowing my controller is no bottleneck to current or future use and can do so much.

The claims for 20 to 43% increase efficiency are bogus which makes all the other claims suspect.
We have a high voltage panel that typically puts out 43V at the controller in full sun with no tilt. It is run through a Morningstar Sun Saver MPPT controller and I monitor using a Victron battery monitor. The high voltage means you get some usable current even in shaded areas. Just for fun I measured voltage from a full moon and got 12.7V.
The review in the Wind & Sun forum http://www.wind-sun.com/ForumVB/showthread.php?17511-Eco-Worthy-20a-MPPT-charge-controller-review

The RV net forum discussion http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26464298/srt/pa/pging/1/page/2.cfm

Quote:
Also, an MPPT controller will allow your panels full output to be better utilized than with a PWM controller. If you're going with a larger (less expensive watt/dollar) panel it will likely have a high enough Vmp that you will need a MPPT controller anyway.
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Again, FYI, I see MPPT controllers all the time for $59
Try one, you mite like it.

KD4UPL wrote:
A cheap (poor) charge controller can cause lots of problems. It's not the place to skimp. You want one that has programmable charging set points so you can charge your batteries to the manufacturer's specifications. A poor controller can overcharge or undercharge your batteries. Also, an MPPT controller will allow your panels full output to be better utilized than with a PWM controller. If you're going with a larger (less expensive watt/dollar) panel it will likely have a high enough Vmp that you will need a MPPT controller anyway.
RV usage, I guess because of price, is one of the last places PWM controllers are installed anymore. The home, cabin, grid tied solar industry has almost completely moved to MPPT controllers for all of their advantages.
I would highly recommend Blue Sky charge controllers.

FYI, there are fully programmable controllers out there for as cheap as $12.50.It has so many adjustments, I don't know what 1/2 of them are for, but I know the first one (of 10) was adjustable for 5 different types of batteries. It worked perfect, but its only a 10 amper, so its now setting in my solar acumulation box.
The $10 (non prog) 15 amp ebay china controller I have now, brings my batteries into float mode at exactly the same voltage as my PD 9245, so thats good enuff for me.
Just because you spent big bucks for morningstar, doesn't mean you have to to get a controller that works just as well,
But, being a short timer, I can't speak for the longtivity of the cheap priced controllers, but I will tell you that I really couldn't care less, when I can buy 2 dozen spares for what you spent on a morningstar. And I can change it out in 3 minutes.
Now, having said that, you will notice that the purpose of my above post was to advise a nuby like myself to think about handling and storage of smaller panels verses large heavy ones,.....not to sell cheap china controllers.

Hi,


Here is a simple flow chart.

Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT.

Here is a link to the rather special spreadsheet that N8GS has created to help size solar battery charging systems!
Solar Spread Sheet N8GS

A cheap (poor) charge controller can cause lots of problems. It's not the place to skimp. You want one that has programmable charging set points so you can charge your batteries to the manufacturer's specifications. A poor controller can overcharge or undercharge your batteries. Also, an MPPT controller will allow your panels full output to be better utilized than with a PWM controller. If you're going with a larger (less expensive watt/dollar) panel it will likely have a high enough Vmp that you will need a MPPT controller anyway.
RV usage, I guess because of price, is one of the last places PWM controllers are installed anymore. The home, cabin, grid tied solar industry has almost completely moved to MPPT controllers for all of their advantages.
I would highly recommend Blue Sky charge controllers.

Those big house panels are cheaper $ per watt, but for portable use, they are big and heavy.
I elected to go w/ 2 smaller lighter, easier to store panels And a $10 15 amp controller works fine w/ them too..

That I will deffently do.

If you want to use a low cost PWM controller then look only at 12v panels.
12 volts is nominal. Actual voltage will be 17 to 22. Controller cuts voltage to charge properly.

This type of system you want to compare Isc or Imp for choosing a panel.
Isc = Amps at short circuit
Imp = Amps at max power

Post a link to the items before you spend money.

Agreed. I did a lot of research on both my batteries and panels, and still have not actually mounted anything to the RV. I am still using what I have at the house instead. You certainly can rush in, but requirements change with experience.

Jim