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electrical:solar:charge_controller [2021/07/07 16:54]
frater_secessus [PWM]
electrical:solar:charge_controller [2024/02/16 23:32] (current)
frater_secessus [how to choose] added video
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 [[lifestyle:words_of_wisdom|Words of wisdom]]:  //"Any Solar is better than no solar, but having too much solar is difficult. The best solar systems are those which can keep the batteries the happiest.  Happy batteries are those which are recharged quickly after depletion."//((http://www.cheaprvliving.com/forums/Thread-Should-I?pid=88971#pid88971)) - SternWake [[lifestyle:words_of_wisdom|Words of wisdom]]:  //"Any Solar is better than no solar, but having too much solar is difficult. The best solar systems are those which can keep the batteries the happiest.  Happy batteries are those which are recharged quickly after depletion."//((http://www.cheaprvliving.com/forums/Thread-Should-I?pid=88971#pid88971)) - SternWake
 ====== Solar charge controllers ====== ====== Solar charge controllers ======
 +
 +===== TLDR =====
 +
 +  * solar panels -> solar charge controller (SCC) -> battery bank
 +  * the SCC's main job is preventing //battery overcharge//
 +  * The two main types of SCC are PWM and MPPT
 +    * PWM - Cheaper, less efficient
 +    * MPPT - More expensive, but more efficient
 +  * SCC LOAD outputs are vestigial features but may be useful for triggering certain loads
 +
 +
 +[[opinion:frater_secessus:pareto|about this summary]]
 +
 +
 +==== overview ====
 +
 +
 +
 A solar charge controller (CC) regulates the [[electrical:12v:charging|charging]] of a [[electrical:12v:deep cycle battery|battery bank]] from the [[electrical:solar:panels|solar panels]]. A solar charge controller (CC) regulates the [[electrical:12v:charging|charging]] of a [[electrical:12v:deep cycle battery|battery bank]] from the [[electrical:solar:panels|solar panels]].
 Counterintuitively, the primary job of the charge controller (CC) is to keep the batteries from being //over//charged.  Solar panels run at higher voltages than batteries, often at voltages high enough to damage the batteries.  The CC provides the correct amount of power the battery needs at the correct time;  this is called [[electrical:12v:charging|smart or three stage charging]]. Counterintuitively, the primary job of the charge controller (CC) is to keep the batteries from being //over//charged.  Solar panels run at higher voltages than batteries, often at voltages high enough to damage the batteries.  The CC provides the correct amount of power the battery needs at the correct time;  this is called [[electrical:12v:charging|smart or three stage charging]].
 Charge controllers are generally **rated by the amount of output they can provide**. This output is shared by charging circuits and [[#using_load_output|LOAD circuits]].  For example, a 20A controller might be using 18A for charging and have 2A available for LOAD. Charge controllers are generally **rated by the amount of output they can provide**. This output is shared by charging circuits and [[#using_load_output|LOAD circuits]].  For example, a 20A controller might be using 18A for charging and have 2A available for LOAD.
 Controllers operate based on [[electrical:solar:charge_controller_setpoints|factory- or user-defined setpoints]] (values) stored internally. Controllers operate based on [[electrical:solar:charge_controller_setpoints|factory- or user-defined setpoints]] (values) stored internally.
-===== types of charge controllers =====+ 
 +Cautionary example:  [[https://www.youtube.com/watch?v=z5RtZe9AW2E|12W Unregulated Panel vs. 220Ah AGM Bank]] 
 +===== specs ===== 
 + 
 +Regardless of type, controllers will have several specifications in common.  
 + 
 +  * **rating (or "size")** - this is usually the maximum output in A (amps) the controller can produce (charging + loads).((for technical reasons with PWM this will also be the *input* current limit)) 
 +  * **12v/24v/48v** - this refers to the nominal voltage of the battery bank it will be charging.  
 +  * **Maximum input voltage** - the highest voltage the controller should //ever// see from the solar array.((it is common to leave ~20% margin))  NOTE: a 50v input max does //not// mean a PWM controller can make efficient use of mismatched panel/battery voltages; that requires MPPT.  See [[#how_to_choose|how to choose]] below. 
 + 
 + 
 + 
 +===== Types of charge controllers =====
 [note from frater secessus: PWM vs. MPPT debates can get overheated in forums and comments. It's your money and your build so do it the way that meets your needs.] [note from frater secessus: PWM vs. MPPT debates can get overheated in forums and comments. It's your money and your build so do it the way that meets your needs.]
 +
 +=== The quick and dirty === 
 +
 +**PWM** is much less expensive, and typically makes less power over the course of the day. Panel voltage and battery bank voltage need to be matched. 
 +
 +**MPPT** is more expensive and but typically makes more power, especially when battery voltage is low.   Panel voltage and battery bank voltage can diverge. 
 +
 +The more power / less power dynamic is highly dependent on the setup and use case; there are no definite answers about which is right for you.  For example, there are edge scenarios where PWM can make more power than MPPT.((like high ambient temps + low Vmp panels))
 +
 +
 ==== PWM ==== ==== PWM ====
 [[http://amzn.to/2hcZaj2|{{ https://images-na.ssl-images-amazon.com/images/I/41pwJOriZHL._AC_US160_.jpg}}]]**PWM** (pulse width modulation) controllers charge by connecting panels to battery until a given voltage setpoint is reached.  When the desired setpoint is reached the controller switches current on/off to the battery in very fast cycles and in such a duration needed to keep voltage from rising.  This time slicing power delivery is called is pulse width modulation, or PWM.  Some heat will be generated by the switching. Counterintuitively, the PWM may be cooler the touch when it is running full open because there is no switching going on to limit voltage. [[http://amzn.to/2hcZaj2|{{ https://images-na.ssl-images-amazon.com/images/I/41pwJOriZHL._AC_US160_.jpg}}]]**PWM** (pulse width modulation) controllers charge by connecting panels to battery until a given voltage setpoint is reached.  When the desired setpoint is reached the controller switches current on/off to the battery in very fast cycles and in such a duration needed to keep voltage from rising.  This time slicing power delivery is called is pulse width modulation, or PWM.  Some heat will be generated by the switching. Counterintuitively, the PWM may be cooler the touch when it is running full open because there is no switching going on to limit voltage.
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 [[https://diysolarforum.com/threads/why-is-mppt-better-than-pwm.24892/post-295861|For technical reasons]] PWM can deliver more current than the panels' Imp, even nearing Isc. [[https://diysolarforum.com/threads/why-is-mppt-better-than-pwm.24892/post-295861|For technical reasons]] PWM can deliver more current than the panels' Imp, even nearing Isc.
 +
 +=== panel selection for PWM ===
 +
 +PWM makes the most power when coupled with panels whose operating [[electrical:solar:panels#specifications|Vmp]] is very close to the controller's Absorption ("boost") voltage [[electrical:solar:charge_controller_setpoints|setpoint]].  Since [[electrical:solar:output#panel_temperature|ambient temperatures affect operating Vmp]] the panel's Vmp spec on the label should be about 10% higher than Absorption voltage.  
 +
 +Examples:
 +
 +  * 16.28v Vmp panel spec would be optimal for 14.8v Absorption, as we might use for flooded lead acid.  14.8v x 1.1 = 16.28v.
 +  * 15.62v Vmp panel spec would be optimal for 14.2v Absorption, as we might use for Gel or LiFePO4.  
 +
 +
 +Some [[electrical:solar:panels#thin_film|thin-film]] panels have Vmp in that range but most panels are much higher.  So we find the lowest Vmp practical.  17Vmp panels would perform better on PWM than 18v or 19v.
 ==== MPPT ==== ==== MPPT ====
 [[http://amzn.to/2iD3WKf|{{ https://images-na.ssl-images-amazon.com/images/I/51bi9IjcsRL._AC_US160_.jpg}}]] [[http://amzn.to/2iD3WKf|{{ https://images-na.ssl-images-amazon.com/images/I/51bi9IjcsRL._AC_US160_.jpg}}]]
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 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).   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.+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, depending on conditions.  //Average// daily production with MPPT is typically ~+15%((https://web.archive.org/web/20221012213623/https://www.redalyc.org/journal/849/84959429001/html/)), which may or may not justify the added cost on its own  
 + 
  
 === "boost" effect === === "boost" effect ===
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 There are some considerations when [[electrical:solar:mppt design|designing a system around an MPPT controller]]. There are some considerations when [[electrical:solar:mppt design|designing a system around an MPPT controller]].
 +
 +== panel selection for MPPT ==
 +
 +MPPT thrives on voltage.  In general, we should select panels that have the highest-practical Vmp while staying safely under the controller's voltage input limit.   MPPT efficiency tends to be greatest when panel voltage is ~twice the charging voltage. The exact ratio varies by controller so read the docs for specifics.  
 +
 +Note that [[electrical:solar:series_vs_parallel|panels can be run in series]] to increase their voltage. 
 +
 +
 +== when PWM beats MPPT ==
 +
 +There are edge cases where an optimal PWM setup can make //more// power than MPPT for a time.  This can happen because MPPT has DC-DC losses that PWM does not, typically ~5%.  Since MPPT harvest from the panel is typically 10-30% greater than PWM the DC-DC losses are hidden.  
 +
 +But when PWM controllers and panels are optimally matched (difference between panel Vmp((actual, not spec)) and Absorption(("boost")) voltage is <5%) then PWM will make a bit more power during Absorption.  
 +
 +
 +
 +
 +
 +
 ==== shunt  ==== ==== shunt  ====
 +
 +see article below
 +
 +
 +==== single-stage chargers ====
  
 [[http://amzn.to/2yQppTX|{{ https://images-na.ssl-images-amazon.com/images/I/41Gwyw0BT5L._AC_US160_.jpg}}]] [[http://amzn.to/2yQppTX|{{ https://images-na.ssl-images-amazon.com/images/I/41Gwyw0BT5L._AC_US160_.jpg}}]]
-In this usage, //shunt controllers// are single-stage chargers that hold the bank at a [[electrical:solar:charge_controller_setpoints|setpoint]] (Vdisconnect)((whether generally or exactly)) as long as sufficient solar harvest is present.  When the setpoint voltage is achieved the controller is turned off for some amount of time.((In a hydro or windpower scenario the power cannot be turned off and is diverted (shunted) instead to a diversion load like water heating, water pumping, etc.))+Single-stage chargers hold the bank at a [[electrical:solar:charge_controller_setpoints|setpoint]] (Vdisconnect)((whether generally or exactly)) as long as sufficient solar harvest is present.  When the setpoint voltage is achieved the controller current is turned off for some amount of time.((In a hydro or windpower scenario the power cannot be turned off and is diverted (shunted) instead to a diversion load like water heating, water pumping, etc.)) There are several different ways of turning off the current:
  
-Technical note:  //shunts// short out the panels to control ON/OFF charging.  //Series chargers// behave similarly but open-circuit the panels.   //PWM// is like a superfast series charger whose ON/OFF cycles are so fast that an average voltage can be held.((it actually does it by varying the width of the ON periodsresulting in a percentage of ON time))+  * PWM - open circuit the panels very rapidly (tens-to-thousands times a second)and for varying lengths of time to hold the voltage setpoint more precisely.  Same as PWM controllers above, but in this market range the modulation tends to be cruder/slower and there is only one charging voltage setpoint. 
 +  * shunt shorts the panels ON/OFF (charge-and-stop, less common)  
 +  * series - open circuits the panels ON/OFF (charge-and-stopless common)
  
 Simple versions use simple electronics((as with [[https://www.flexcharge.com|Flexcharge]])) or relays to turn charging on until Vdisconnect is reached, at which point charging is turned off off. If/when voltage falls to some lower voltage (Vreconnect) charging begins again.  This is sometimes called [[electrical:12v:charging#charge-and-stop|charge and stop charging]] or on/off charging.  Voltage tends to wander a bit as the charging stops and starts.  They are often used where extreme simplicity/robustness is required, or where more complex electronics might cause electrical interference.((as in a ham shack)) Simple versions use simple electronics((as with [[https://www.flexcharge.com|Flexcharge]])) or relays to turn charging on until Vdisconnect is reached, at which point charging is turned off off. If/when voltage falls to some lower voltage (Vreconnect) charging begins again.  This is sometimes called [[electrical:12v:charging#charge-and-stop|charge and stop charging]] or on/off charging.  Voltage tends to wander a bit as the charging stops and starts.  They are often used where extreme simplicity/robustness is required, or where more complex electronics might cause electrical interference.((as in a ham shack))
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 > If your charge controller only holds [absorption] voltage for an hour or two, that is likely not enough time. As long as [there is a load] and you cycle the battery daily, you could set float voltage to 14.8v [to match absorption] without worry. Only when you stop cycling the battery do you need to return float voltage to more regular 13.2v levels. Premature application of float voltage by automatic charging sources is a battery killer.((http://www.cheaprvliving.com/forums/Thread-Solar-or-Battery-Problem?pid=229883#pid229883)) > If your charge controller only holds [absorption] voltage for an hour or two, that is likely not enough time. As long as [there is a load] and you cycle the battery daily, you could set float voltage to 14.8v [to match absorption] without worry. Only when you stop cycling the battery do you need to return float voltage to more regular 13.2v levels. Premature application of float voltage by automatic charging sources is a battery killer.((http://www.cheaprvliving.com/forums/Thread-Solar-or-Battery-Problem?pid=229883#pid229883))
 +
 +Also see [[https://goughlui.com/2020/06/05/teardown-tested-generic-kw12x0-w88-solar-charge-controller-10-30a-versions/|this comprehensive teardown]] that assesses:
 +
 +> ....a rather inexpensive piece of equipment but it doesn’t do a terrible job of being a basic solar charge controller. On the whole, it behaves as one may expect – protecting the battery from excessive voltage and overdischarge, with an integrated dusk timer function and USB outputs...what do you expect for $10-20? Something that works is already a big surprise to me.
 +
 +=== with Bnn settings ===
 +
 +Units with Bnn settings purport to have Absorption((which they often call Equalization)) profiles for various batteries and configurable Float setpoints. 
 +
 +  * B01 - Sealed lead acid (AGM), typically 14.4v
 +  * B02 - Gel, typically 14.2v
 +  * B03 - flooded lead acid, typically 14.6v
 +  * B04 - 4S LiFePO4 <-- like [[electrical:12v:drop-in_lifepo4|drop-in LFP]]
 +  * B05 - 5S LiFePO4 (uncommon)
 +  * B06 - 3S Li-NMC
 +  * B07 - 4S Li-NMC
 +
 +Absorption duration is unknown.
 +
 +Example manual for controller with [[https://www.botnroll.com/img/cms/FAL09014-Solar-PWM-10A-USB-Manual.pdf|B01-B03]] and [[https://www.solorder.se/image/data/uploads/KLD1210.pdf|B01-B07]].
 +
 +
 +Further viewing:
 +
 +
 +  * [[https://www.youtube.com/watch?v=Fmfnxkh1IFo|basic setup]] by Scott
 +  * [[https://www.youtube.com/watch?v=v-iLu9DS558|setting up the LOAD functions]] by Scott
 +
 +==== USB converters ====
 +[[https://amzn.to/3msdCUU|{{ https://m.media-amazon.com/images/I/71EmsM+loWL._AC_SY200_.jpg?50}}]] 
 +These aren't controllers in the normal sense, but there are [[https://amzn.to/3msdCUU|modules]] that connect to your panel's MC4 connectors and output USB power.  
 +
 +If you only need 5v USB power up to 2.5A per port this may be a workable solution. 
  
 ==== DDCCC ==== ==== DDCCC ====
 [note:  this is a placeholder for a possible new entry.] [note:  this is a placeholder for a possible new entry.]
 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]]. 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]].
 +
 +
 +==== boosting ====
 +
 +Most charge controllers that convert voltage do it by //bucking// (reducing) panel voltage down to the appropriate charging voltages.((normal PWM don't reduce/convert voltage in the normal sense;  they run the panels ~at bank voltage))
 +
 +//Boosting// (voltage-increasing) controllers do exist ([[https://amzn.to/3Rh6QSu|example]]) but they are niche products.  In most cases it makes more sense to increase panel voltage with serial wiring. 
 ==== how to choose ==== ==== how to choose ====
 **PWM is a reasonable default choice** in typical scenarios((12v house power, 12v panels)); 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 typical scenarios((12v house power, 12v panels)); 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] 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]
  
-PWM's limitations are reduced when [[electrical:12v:alt_and_solar|other forms of charging are present to help]], and when battery voltage is relatively high: +There are also edge cases where //PWM can actually make more power than MPPT//.  An example of this might be low-Vmp poly [[electrical:solar:panels|panels]] during Absorption stage in very hot weather, due to MPPT DC-DC conversion losses and [[electrical:solar:output#panel_temperature|temperature derating]].
- +
-There are also edge cases((low altitude, high temperature, Absorption)) where PWM can actually make more power than MPPT.  An example of this might be low-Vmp poly [[electrical:solar:panels|panels]] during Absorption stage in very hot weather, due to MPPT DC-DC conversion losses and [[electrical:solar:output#panel_temperature|temperature derating]].+
  
 **MPPT is effectively required** when: **MPPT is effectively required** when:
-  * using panels with nominal voltages higher than 12v ((more presciselywhen panel nominal voltage exceeds house bank nominal voltage))+  * when one needs to squeeze every watt out of the panel 
 +  * using panels with nominal voltages higher than the battery bank voltage, like 24v panels with a 12v bank.   To be fair[[http://mouse.mousetrap.net/blog/2021-07-09-solar-back-online-.html#pwm-spare-saved-my-bacon|one really can use higher-voltage panels with PWM and 12v banks]] -- they just end up running at about half power.  [[https://www.youtube.com/watch?v=V2b7z2eTb5o|Demonstration video from AltE]].
   * space available for panels is limited, as on a sailboat or small vehicle   * space available for panels is limited, as on a sailboat or small vehicle
   * daytime loads are hampered by [[electrical:solar:pwm_tweaking|PWM Vbatt hobbling]]   * daytime loads are hampered by [[electrical:solar:pwm_tweaking|PWM Vbatt hobbling]]
   * [[#overpaneling|overpaneling]]   * [[#overpaneling|overpaneling]]
   * making [[electrical:converter#diy_converters|DIY converters]]   * making [[electrical:converter#diy_converters|DIY converters]]
-We say "effectively required" because one //can// use 24v panels with PWM and 12v banks -- it just doesn't work very well.  The 24v panels will be run at 12v voltages, yielding about half the power you would get with MPPT. + 
  
 Further reading:   Further reading:  
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 **MPPT may be a better fit** when: **MPPT may be a better fit** when:
  
-  * the existing PWM system is not providing enough output+  * the existing PWM system is not providing enough output but is close (like 10%-20% shortfall)
   * 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]].   * 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]].
   * battery banks are cycled deeply on a regular basis so more time is spent at low Vbatt where PWM struggles.   * battery banks are cycled deeply on a regular basis so more time is spent at low Vbatt where PWM struggles.
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 See also [[electrical:solar:shunt_tweaking|shunt tweaking]]. See also [[electrical:solar:shunt_tweaking|shunt tweaking]].
 +
 +==== should I upgrade my PWM to MPPT? ====
 +
 +If the system has changed and now MPPT is required for one of the reason above, then yes.
 +
 +But most people consider this switch to make "more power", forgetting that **solar only makes power when it is demanded**.((for loads or charging))  //If you are presently consuming every watt the system can make// then, yes, replacing PWM with MPPT will likely increase your harvest by ~15%. If you aren't hammering the system then +15% is immaterial; there is no difference in the performance of a 150mph car and a 165mph car in a school zone.
 +
 +So the questions are:
 +
 +  -  do you need more power than you are getting now?
 +  -  would +15% be enough to meet your needs
 +  -  if so, would you pay [whatever the MPPT costs] to get that +15%?
 +
 +There is a saying in solar circles that "adding another panel is a better deal than upgrading from PWM to MPPT."  This may or may not be true in your particular use case.   
  
 ===== multiple charge controllers  ===== ===== multiple charge controllers  =====
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 As with [[electrical:inverter|inverters]], sizing the controller correctly will help system efficiency and save money.  An oversized CC will have unnecessarily high parasitic drains as it powers itself and will cost more.  An undersized CC will not be able to put all the rated solar wattage to use and will leave no room for expansion. As with [[electrical:inverter|inverters]], sizing the controller correctly will help system efficiency and save money.  An oversized CC will have unnecessarily high parasitic drains as it powers itself and will cost more.  An undersized CC will not be able to put all the rated solar wattage to use and will leave no room for expansion.
 For PWM controllers, the formula is something like (panel wattage / 13) * (1.2 oversize for safety) = charge controller amps.((https://www.altestore.com/howto/sizing-pwm-solar-charge-controllers-a91/))  For PWM controllers, the formula is something like (panel wattage / 13) * (1.2 oversize for safety) = charge controller amps.((https://www.altestore.com/howto/sizing-pwm-solar-charge-controllers-a91/)) 
-MPPT controllers have more leeway in sizing since they can control the output of the panels independently of battery voltage.  +MPPT controllers have more leeway in sizing since they can [[electrical:solar:overpaneling|control the output of the panels]] independently of battery voltage.  
 See also [[electrical:solar:sizing|Sizing a Solar Installation]] See also [[electrical:solar:sizing|Sizing a Solar Installation]]
 ===== overpaneling ===== ===== overpaneling =====
 this section [[electrical:solar:overpaneling|has been moved]]. this section [[electrical:solar:overpaneling|has been moved]].
 ===== Using LOAD output ===== ===== Using LOAD output =====
-It is common for charge controllers to have a LOAD output for powering (or switching) loads.  One benefit to doing this is you can define a [[electrical:12v:lvd|Low Voltage Disconnect]] (LVD) setpoint and Low Voltage Reconnect to protect the battery from excessive discharge. + 
-Not all types of loads should be run from these terminals, though.  Morningstar says:+It is common for charge controllers to have a LOAD output for powering (or switching) loads.  A common-and-understandable misperception is that it is there to run your loads.  Kinda.   
 + 
 + 
 +==== historical use ==== 
 + 
 +LOAD terminals were originally used to control nighttime lighting, like pathway or garden lights.  These are relatively small, resistive loads.  Power to the LOAD terminal could be associated with sun (or lack of sun) and/or battery voltage.  
 + 
 +==== present use ==== 
 + 
 +In practice the LOAD terminals typically are either ignored((some well-respected controllers don't have them anymore)) or used as [[electrical:12v:lvd|low voltage disconnect]] power relays.  You can define Low Voltage Disconnect (LVD) and Low Voltage Reconnect (LVR) [[electrical:solar:charge_controller_setpoints|setpoints]]  to protect the battery from excessive discharge. 
 + 
 +==== why loads aren't powered from LOAD terminals ==== 
 + 
 + 
 +> The load outputs take power from the battery terminals.... the only advantage in using the load terminals is displayed info and the ability to disconnect the load at programmable voltage levels. -- mikefitz((https://diysolarforum.com/threads/epever-solar-charge-controller-false-measurements-on-the-load.23995/post-283823)) 
 + 
 +Some loads are inappropriate for the LOAD output.  Morningstar says: 
 >  Heavily inductive or capacitive loads such as **pumps, motors, compressors, and  >  Heavily inductive or capacitive loads such as **pumps, motors, compressors, and 
 inverters** should not be wired to the controller’s Load terminals. In addition, loads exceeding the Load Current Rating of the controller should not be connected to the controller’s Load terminals.((http://support.morningstarcorp.com/wp-content/uploads/2014/07/ALL.DIG_.Load_Control_Using_A_Relay.01.EN_.pdf)) inverters** should not be wired to the controller’s Load terminals. In addition, loads exceeding the Load Current Rating of the controller should not be connected to the controller’s Load terminals.((http://support.morningstarcorp.com/wp-content/uploads/2014/07/ALL.DIG_.Load_Control_Using_A_Relay.01.EN_.pdf))
 +
 elsewhere they say: elsewhere they say:
 +
 >  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))  >  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)) 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))
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 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. 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.
 +
 +
 +===== connection order =====
 +
 +Solar charge controllers use the battery bank to provide a reference voltage for operation.  For this reason **the battery should always be present when solar panels are connected**.  This suggests a particular order for connection/disconnection/resetting:
 +
 +  - disconnect solar panels
 +  - disconnect battery
 +  - wait a moment
 +  - connect battery, wait for controller to power on
 +  - connect solar panels
 +
 +
 +For an overview of official procedures by manufacturer, see [[https://www.reddit.com/r/vandwellers/comments/12fmyrl/solar_system_is_not_functioning/jfm66y0/|this post]]. 
 +
 +
 ===== positive ground controllers ===== ===== positive ground controllers =====
 Some controllers are labeled or described as "positive ground", often by their competitors.  The term is incorrect and misleading: Some controllers are labeled or described as "positive ground", often by their competitors.  The term is incorrect and misleading:
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 > The reason for the low side switching is the intersection between physics and economics.  N-channel field effect transistors are faster, better, cheaper than P-channel parts.  The designer can A) use good parts in a simple circuit or B) use more expensive not so good parts or C) make a complicated circuit that uses 18 volts to control a 15 volt switch.((http://www.cheaprvliving.com/forums/showthread.php?tid=24605&pid=307539#pid307539)) > The reason for the low side switching is the intersection between physics and economics.  N-channel field effect transistors are faster, better, cheaper than P-channel parts.  The designer can A) use good parts in a simple circuit or B) use more expensive not so good parts or C) make a complicated circuit that uses 18 volts to control a 15 volt switch.((http://www.cheaprvliving.com/forums/showthread.php?tid=24605&pid=307539#pid307539))
  
 +===== further reading =====
 +
 +  * [[https://www.solar4rvs.com.au/buying/buyer-guides/choosing-the-right-solar-charge-controller-regulat/|exceptional article on charge controllers]] by Solar4RVs
electrical/solar/charge_controller.1625691266.txt.gz · Last modified: 2021/07/07 16:54 by frater_secessus