MPPT solar charge contoller.....EXELLENT!

[Frank]

I just replaced my old style controller with a Blue Sky 2000E

Totally impressed!!

I had actually ordered new batteries, but woke up this morning to 12.46V running refridge all night and no sun since 4:40pm yesterday afternoon.

You get over 20% more charge from the same sunlight and they also have a "bettery equalization" mode.... a controlled overcharge to 15.2V for between 1 and 2 hours.  It cleans the plates. I did this yestersay for 1.5 hours and have to say.....looking like new batteries are not needed.

Money well spent!

[ralay]

We've been thinking about getting one as well.  What model did you buy?

[Frank]

I just replaced my old style controller with a Blue Sky 2000E

Totally impressed!!

;D :o

I should clarify....I have a big panel at 230 watts, so a heavier controller.
The Blue Sky 2000E is a 25amp controller.
There are several MPPT controllers from reputable company's in the$65 range for 100 watt panels
  a genasun GV-10 which is a MPPT Charge controller is designed for smaller solar panels.  Smaller meaning up to 125 watts. A good buy.
The fellow that wrote this says "do NOT buy on Ebay"...you'll get ripped off.
Well worth the read

http://www.pbase.com/mainecruising/solar_controller_testing

PS....my 120 cord has never been out of the package. Solar only for 2nd season.

[w00dy]

Grog for sharing, Frank. That was a good read, and informative.

[Frank]

Always happy when a product exceeds expectations.
I'm still amazed at the improvement!

[ralay]

I realized that you answered my question in your first post, but I'm glad you replied, because it gave me a chance to read that link.  Double grog. 

We have one 75W panel that is not cutting it and are considering getting another panel.  I was thinking, is it possible to get an MPPT controller that will charge a 12V bank from a 24V panel array (2 12V panels in series)? Is there any advantage to such a setup vs 2 12V panels hooked up in parallel?  Smaller wire running from panels to controller?  Thoughts?

[ralay]

Also, does anyone have any links to good explanations of how MPPT controllers work or of IV curves?  The explanations I find are either super simplistic or so detailed they sound like Star Trek babble. 

If I understand so far, the nature of PV cells is such that as voltage increases, current remains constant until around .5V/cell or ~18V/typical boat panel at which point it crashes to zero at the open circuit voltage.  Even though current remains constant, wattage (power) increases because voltage is increasing and P=IE.  The MPPT is the point of maximum power because it occurs at the highest voltage before the crash. 

:o This blows my mind a little, and if I'd had to guess at an IV curve for a solar cell naively, I wouldn't have drawn one that looked like this.  I'd draw one where current increased with voltage, like all the simple examples on wikipedia's entry on IV curves.  What's up with solar cells?  Do they have some sort of internal resistance that increases with voltage?  Inquiring minds need to know...

[Frank]

Way tooooo cimplicated for me to answer.  Electronics are a weak spot in my brain.  Better with wood, fiberglass and diesels   ;D

That said.....not liking the sound of 24 to 12V
I'd be thinking parallel is better

Another thought....One big panel is easier-simpler than 2 smaller ones.
Prices have come way down now.  Under $1/watt is common

A 200 watt panel does a lot!

[ralay]

The conventions for electricity make things even worse.  Apparently, current being generated has been dubbed "negative" so all electrical engineering explanations show IV curves down in the 4th quadrant (with negative values for current rising toward zero).  This must blow folks' minds, because all the layman's explanations have the whole curve flipped upside down with positive current values falling towards zero.  My question is still the same in either case, but this just makes it doubly confusing when trying to read about it from different sources.  :'( 

We'd get one big panel , if we didn't already have 1 medium sized one.  What don't you like about the sound of 24V to 12V assuming that we're probably going to wind up with 2 panels either way?  Not saying we're set on it, just curious why it would/wouldn't work.

[Frank]

24 volts going into a 12V charge controller to charge 12 V batteries just don't sounf right in my simple mind.....
You've totally lost me on IV curves and 4th quadrants etc.....
Best let a more electronically guy respond....."me dumb"

Built homes all my life.
For sidewalks I'd order "45MPA, 6in slump,air entrainment and fiber"
That lingo I understand    ;D

[ralay]

MPPT are DC-DC converters that can switch between voltage:current ratios.  For instance, 4A from a 12V panel is 48W.  2A from a 24V panel is also 48W.  If you have a regular PWM charge controller, you'd have to throw away half the power from a 24V panel, which would be stupid.  If you have a MPPT controller rated for >24V, you should be able to take 2A from a 24V panel and convert it to 4A to send to your 12V batteries.  You'd also be able to use smaller wire/have less voltage drop to transport 2A vs 4A.  I have no idea if there are models with enough user-adjustable settings to set it all up correctly. 

Also, we probably wouldn't do this just because we'd have to get another 75W panel (vs a 100W or 150W) if I was going to hook them up in series vs. in parallel.  These are just my rainy day brainstorming exercises.

[SailorTom]

They are just DC-DC transformers. Stepping up/down voltage. Typically in EE electron current flow is negative( since an electron has a negative charge) while hole flow is considered positive. There should be blocking diodes to keep from having reverse flow when the PV panels are shaded.

I had a Blue Sky 2000E about 10 years ago, at the time it was marketed to the RV industry. It was well made and I kept hold of it through a couple boats. But like you said low power rating.

[ralay]

Well, after some more research, I read that MPPT controllers work best with single large panels or identical multiple panels.  Since it's not possible to get a new panel to match our old, current panel, we'll probably just stick with our current charge controller and put our money toward a second panel.  This was still good food for thought, Frank, thanks for bringing it up.