jss06 wrote:The biggest advantage a MPPT Controller has is when it is used with a high voltage panel. It will charge better in partial shade than a PWM.
know I can run the CPAP's 2 1/2 days on a group 27 105 amp hour battery. The plate on the Cpap says 2.5 amps time 2( for 2 cpap's)=5 amps.
KennethW wrote:If I am informed right the high volts and a mppt controller will give me more watt into the battery even in low light conditions.
Am I right?
MtnDon wrote:know I can run the CPAP's 2 1/2 days on a group 27 105 amp hour battery. The plate on the Cpap says 2.5 amps time 2( for 2 cpap's)=5 amps.
How far does that draw down the battery? 5 amps x 12 volts for 8 hours a night (a guess) = 480 watt hours
the 105 AH battery x 12 volts = 1260 watt hours
So it seems the load would draw the batteries down 480 /1260 = 38% in one night. Two days on just CPAP would draw the battery down to less than 25%. Not good for the battery.
To replace the CPAP used energy of 480 watt hours with panels that would provide a useful 100 watts all the time would need 480 / 100 = 4.8 hours of "perfect" sunshine. That's not possible in many places.
How much space have you available on the TD roof for solar panels? Could you fit a larger, so called 24 volt or grid tie panel? You could get a brand new panel of around 250 watts from solarblvd.com delivered to most places in the US for about the same cost per watt price as the used panels. You might even be able to buy a single panel locally from some solar dealer / installer who specializes in grid tie solar. Some of them don't mind selling a single panel. That would save the high freight on a single panel.
bdosborn wrote:There's one member here that swears by it. However, when I posed the question to the solar forum, the answer was probably not . The panels you linked are *barely* usable for 12V system with a Vmp of 14V. A better number would be somewhere around 17V. So if you do plan on buying them, I would plan on running them in series to get the voltage up to a better charging level. Of course you'll need an MPPT controller or a high voltage PWM controller if you do.
MPPT controllers are so spendy that any money you save on the eBay panel is more than eaten up by the controller cost. I have an MPPT and a PWM controller on my setup and haven't noticed much of an advantage of one over the other. If it was me, I would buy different panels that are more suitable for 12V battery charging and use a PWM controller. Then you can spend the money you saved from buying the PWM controller on bigger panels. A PWM controller based system gets you the most watts/$. Just make sure you can set your system up so that you can put one on the ground, in the sun, and run a cord back to the controller for the times you're camped in the shade. I get the most amp-hrs/watt from my portable panel as compared to the roof mounted panels since I move it to track the sun whenever I walk by it.
catinmoon wrote:Hi, I just saw this post and am wondering if it is still "current" (ha ha) in 2016? That is, I want a robust solar system for my teardrop, and am wondering if there have been any significant changes since this was initially posted.
afreegreek wrote:catinmoon wrote:Hi, I just saw this post and am wondering if it is still "current" (ha ha) in 2016? That is, I want a robust solar system for my teardrop, and am wondering if there have been any significant changes since this was initially posted.
you would be much better off going to solar system company online and learning about, and how to use solar.. the people who think 12 volt group 24, 27, 31, Marine batteries are actual deep cycle batteries suitable to work as a solar power bank don't have any real knowledge about batteries.. solar panels will easily charge those batteries (to start your motor with) but those type of batteries are not designed to supply DC power.. they are starter batteries.. group GC2 are primarily the smallest size of true deep cycle batteries..
https://www.wholesalesolar.com/ this is a good information site to learn from even if you buy elsewhere..
http://www.solarray.com/TechGuides/Batteries_T.php is also good info.. especially "step to success" section..
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