From: no@never.com   
      
   On Wed, 15 Feb 2017 09:26:41 -0800 (PST), tzelikg@gmail.com wrote:   
      
   >Hi, I was wondering if this would be the correct place to ask questions about   
   new off-grid setups. I'm working on a small cabin after losing my house to a   
   fire and I cant get grid-juice. I have 2 100watt panels, a p20l, and a 12v   
   100ah battery, but I    
   cant seem to get the battery above 11.5 during the day and it dies nightly   
   (its 4 days old). Central New Mexico, so lots of sunshine.   
   >I am running 1-2 small (8-12w) LED bulbs, a wifi router and occasionally my   
   surface pro 3. Also charge my cell phone. I don't understand the setup   
   completely, and my math is flawed as a rule, but it seems like I should have   
   plenty of power unless I'm    
   using the surface a lot.   
      
   First off, STOP!!!  You're murdering that battery.  It will be dead   
   within a week or two of this kind of treatment.   
      
   I have no idea what a p201 is so I'll assume it's some sort of charge   
   controller.  What is the open circuit voltage of your solar cells?   
      
   A "100 watt" cell does not mean that it'll make 100 watts all day.  If   
   the manufacturer is honest, the 100 watt rating will be for high noon   
   at one equatorial reference sun.  Any other place and time and the   
   panel does not generate 100 watts.   
      
   The first thing you need to do is go to nrel.com (national renewable   
   energy laboratory) and determine the reference sun for your latitude   
   and longitude.   
      
   Other important factors include whether the panel is laying flat or at   
   the optimum slope angle and whether you're using a tracker to track   
   the sun across the sky.  Likely your 100 watt panel just laying on the   
   ground, not tracking the sun and not using an MPPT is more like a 20   
   watt panel.   
      
   You're probably going to need something like 600 watts to power your   
   small load.  Next you must get an MPPT controller (Maximum Power Point   
   Tracker)  The MPPT continuously matches the impedance of your battery   
   to the dynamic impedance at every point during the day.  Many MPPTs   
   have outputs to drive a tracker.   
      
   Next, your battery.  NEVER EVER discharge it below about 80% or about   
   12 volts.  Battery chemistries vary slightly so find out from your   
   battery manufacturer what the fully charged rest voltage is, the bulk   
   stage charge termination voltage is, the float voltage and the   
   equalization voltage.  These will be inputs to your MPPT.  If you   
   don't have an MPPT then you must enforce the limits manually.   
      
   A lead-acid battery is properly charged in three stages.  1) bulk  -   
   This is from whatever the charge until about 80%.  During this time   
   the charger outputs maximum current it is capable of while monitoring   
   the rising voltage.   
      
   When the voltage reaches the bulk stage termination voltage, the   
   charger goes into constant voltage mode and enters the absorption   
   stage.  The current gradually tapers off.  What happens next is   
   charger-dependent.  Some chargers use a percentage of the peak bulk   
   current as the trigger point.  Others use a simple timer.  When this   
   point is reached, the voltage is reduced from about 14.1 volts to 13.8   
   and the battery is in float mode.  Really smart chargers will slowly   
   reduce the voltage to about 13.2 volts as the maintenance voltage.   
   Others leave the voltage at 13.8 and allow the battery to use some   
   water (wet cells) or build some pressure (AGM type).   
      
   Over time the state of charge in each cell will vary from the others.   
   The smart charger will charge the battery and then about once a week   
   apply around 14.8 to the battery.  This is called the equalization   
   phase.  Equilization must be done very carefully with AGM or other   
   sealed cells, lest pressure build to the point of the safeties lifting   
   and precious water being lost.  If you have an AGM battery then your   
   MPPT must be designed for or have a setting for AGMs.   
      
   So the very first thing to do is to remove all the load from the   
   battery, get the panels out in the sunlight, sloped in the direction   
   of the sun and let it charge to at least 13.8 volts.  It may take   
   several days.  Once you get it there, never let the voltage fall below   
   12.2 or so (depends on the battery's specific chemistry.  Then get   
   that MPPT and some more panels on order.   
      
   John   
      
   John DeArmond   
   http://www.neon-john.com   
   http://www.tnduction.com   
   Tellico Plains, Occupied TN   
   See website for email address   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)