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--- electrical:solar:charge_controller [2020/05/25 12:02]
frater_secessus [how to choose]
+++ electrical:solar:charge_controller [2020/08/15 21:26]
frater_secessus [MPPT]
@@ Line 15: / Line 15: @@
 [[http://amzn.to/2iD3WKf|{{ https://images-na.ssl-images-amazon.com/images/I/51bi9IjcsRL._AC_US160_.jpg}}]]
 **MPPT** (maximum power point tracking) controllers have two defining abilities:
   - discover (track) and utilize various power points along [[http://samlexsolar.com/learning-center/solar-panels-characteristics.aspx|the panel's power curve]].  Sometimes this is the maximum power point (MPP);  often in a 'dweller context the system needs less power and the controller runs the panels at some other power point.  It might be more accurate to call them PPT controllers.
-  - DC-DC downconvert excess voltage to amps
+  - DC-DC downconvert excess voltage to amps - this is possible because MPPT decouples panel voltage (Vpanel) from charging voltage (Vbatt)
 When maximum power is required((in Bulk or at other time when loads + charging >= panel output)) the controller will run the panels at Vmp (the maximum power point).   At other times the controller will find a less-than-maximum power point to match panel output to system needs.
 [[http://amzn.to/2yP01Ob|{{https://images-na.ssl-images-amazon.com/images/I/512x3hbc6jL._AC_US160_.jpg }}]]
-Since panel voltage at a given power point is usually too high for system needs((particularly with higher than nominal 12v panels )) the controller performs a DC-DC conversion to bring the voltage down to a directly usable level.  Because **current through a conductor is directly proportional to voltage**((https://en.wikipedia.org/wiki/Ohm%27s_law)) this downconversion effectively turns excess voltage into increased amps.(minus conversion losses).
+Since panel voltage at a given power point is usually too
+high for system needs((particularly with higher than nominal 12v panels )) the controller performs a DC-DC conversion to bring the voltage down to a directly usable level.  Because **current through a conductor is directly proportional to voltage**((https://en.wikipedia.org/wiki/Ohm%27s_law)) this downconversion effectively turns excess voltage into increased amps.(minus conversion losses).
 This ability to decouple panel and bank voltage can result in 10%-30% more power harvested from 12v nominal panels than with a PWM controller.  Marketers like to call this "boost" or "gains" but it really just full capture of whatever power the panel[s] can provide under given conditions.
 === "boost" effect ===
 {{ https://media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAwtAAAAJGJhNjE1OGY3LTM3OWQtNGQ2Mi05NWEwLTI2Mzc3MGY3MDk3MA.png?150}}When compared apples-to-apples on identical systems with //only the controller being different//, the "boost" effect is most pronounced:
@@ Line 45: / Line 51: @@
 There are //DC-DC converting charge controllers// (DDCCC) appearing on the market that claim to be MPPT but do not actually track power points (maximum or otherwise).  They do downconvert some excess voltage into amperage.  See [[https://boondockplan.wordpress.com/2017/12/15/backchannel-dc-dc-converting-charge-controllers/|this blog post]].
 ==== how to choose ====
-**PWM is the default choice** in most situations((12v house power, 12v panels)) because they work well enough and are inexpensive. PWM controllers can cost half or a third of their MPPT workmates for any given rated output.((10A, 20A, 40A, etc))
+**PWM is a reasonable default choice** in most situations((12v house power, 12v panels)) because they work well enough and are inexpensive. PWM controllers can cost half or a third of their MPPT workmates for any given rated output.((10A, 20A, 40A, etc))
 If more power is needed (and there is physical space) additional PV can be added to match the charging output of an MPPT charger, often at a lower cost.  [There are no prizes for fanciest or most expensive charge controller!  Do what is best for you -- frater secessus]
@@ Line 64: / Line 70: @@
   * the existing PWM system is not providing enough output
+  * using monocrystalline panels, as the higher Vmp and lower Imp further reduces PWM output.
   * battery banks are cycled deeply on a regular basis so more time is spent at low Vbatt where PWM struggles.
   * nominal 12v panels have a relatively high Vmp (>=18v) for [[https://www.reddit.com/r/vandwellers/comments/bmlosu/is_vandwelling_a_frugal_lifestyle/emz5lsf/?context=1|reasons discussed here]].
@@ Line 96: / Line 103: @@
 >  Inductive loads can generate large voltage spikes that may damage the controller’s lightning protection devices.((http://www.morningstarcorp.com/wp-content/uploads/2014/02/TS.IOM_.Operators_Manual.04.EN_1.pdf))
 although an exception is made for the SunSaver MPPT which "Handles inductive loads without problems."((http://support.morningstarcorp.com/wp-content/uploads/2014/07/SunSaverMPPT-FeaturesBenefits.pdf))
 One can run loads heavier than the controller is rated for (or inductive/capacitive loads) by connecting those load[s] to a relay((http://support.morningstarcorp.com/wp-content/uploads/2014/07/ALL.DIG_.Load_Control_Using_A_Relay.01.EN_.pdf)), which is in turn connected to the LOAD output.  This still allows for Low Voltage Disconnect because the CC will turn off power to the LOAD output, which turns off power to the relay, which turns power off to the load.
 You may also be able to use the LOAD output to create a [[electrical:solar:nonessential|separate 12v circuit for non-essential ("opportunity") loads]].
 Note:  in wind and hydro power applications the output can be sequenced so that LOAD is activated only when batteries are fully charged.  This is called a "dump load" because those power sources need to be able to "dump" excess current to prevent damage to themselves.  Dump loads are not necessary in solar because panels can be open- or short-circuited without damage.
 ===== positive ground controllers =====

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