Differences

This shows you the differences between two versions of the page.

--- electrical:solar:charge_controller [2023/04/11 19:57]
frater_secessus [Solar charge controllers] pareto
+++ electrical:solar:charge_controller [2025/06/20 16:53] (current)
frater_secessus [single-stage chargers]
@@ Line 2: / Line 2: @@
 ====== Solar charge controllers ======
-===== Pareto summary =====
+===== 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
+  * The two main types of SCC are PWM and MPPT
-  * SCC LOAD outputs are vestigal features but may be useful for triggering certain loads
+    * PWM - Cheaper, less efficient
+    * MPPT - More expensive, but more efficient
+  * SCC LOAD outputs are vestigial features but may be useful for triggering certain loads
@@ Line 23: / Line 25: @@
 Cautionary example:  [[https://www.youtube.com/watch?v=z5RtZe9AW2E|12W Unregulated Panel vs. 220Ah AGM Bank]]
+==== sensors ====
+To charge correctly the controller needs to know the precise voltage and temperature of the battery bank.
+In the best case scenario these measurements are done with an external **temp sensor** and **voltage sense**((not a typo, it's called voltage sense)) that plug into the controller or talk to the controller via bluetooth.
+In the absence of external sensors the controller tries to use any internal sensors it might have.  The values will be inaccurate:
+  * battery voltage will read [[electrical:12v:voltage_sag|falsely high during charging]], and
+  * temperature will read falsely high because of the heat the controller generates from its own electronics
+With **lead-chemistry batteries** both conditions can cause [[electrical:12v:psoc|chronic undercharging]], a key cause of [[electrical:batterycide|premature battery failure]].  Many **LiFePO4 batteries** have their own [[opinion:frater_secessus:agm2lifepo4#wait_lfp_can_be_damaged_by_charging_in_cold_weather|low temperature charging cutoff]] but those that do not must rely on the charger to disconnect when battery temps are ~freezing.
 ===== specs =====
 Regardless of type, controllers will have several specifications in common.
-  * **rating (or "size")** - this is usually the maximum output the controller can produce (charging + loads).((for technical reasons with PWM this will also be the *input* current limit))
+  * **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.
+  * **Minimum input voltage** - a PWM controller will requires panel voltage ≥ battery voltage to charge.  MPPT controllers will usually require a bit more voltage headroom to start/run the MPPT algorithm.((although less common, //boosting// MPPT do exist that can increase incoming voltage in order to charge a higher-voltage battery bank))
+  * **Maximum input current** is uncommon in standalone MPPT controllers but common in [[12v:sg_troubleshooting#must_i_use_the_ps_brand_s_proprietary_solar_panels|the controllers built into "power stations"]].  It is also a factor with PWM controllers.
 ===== Types of charge controllers =====
@@ Line 54: / Line 71: @@
 [[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 ====
 [[http://amzn.to/2iD3WKf|{{ https://images-na.ssl-images-amazon.com/images/I/51bi9IjcsRL._AC_US160_.jpg}}]]
@@ Line 68: / Line 97: @@
 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.
@@ Line 83: / Line 113: @@
 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  ====
@@ Line 116: / Line 165: @@
 > ....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.
-Further viewing:
+=== 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:
+  * excellent [[https://www.youtube.com/watch?v=Ezh0ylkAyTw|teardown and analysis]] by Big Clive
   * [[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
@@ Line 131: / Line 197: @@
 [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]].
+==== 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 ====
 **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))
@@ Line 139: / Line 212: @@
 **MPPT is effectively required** when:
   * 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.
+  * 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
   * daytime loads are hampered by [[electrical:solar:pwm_tweaking|PWM Vbatt hobbling]]
@@ Line 152: / Line 225: @@
 **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]].
   * battery banks are cycled deeply on a regular basis so more time is spent at low Vbatt where PWM struggles.
@@ Line 172: / Line 245: @@
 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  =====
 [[electrical:12v:multipoint_charging|Multiple controllers (with separate arrays) can be used to charge a common bank]].  The controllers should be configured with similar charging setpoints for the greatest efficiency.((http://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/))
 ===== sizing your charge controller =====
-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/))
+NOTE:  in no case can the panel voltage limit be exceeded.
-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]]
+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, weigh more, and take up more space.  An undersized CC will either not perform well (MPPT) or be damaged (PWM).
+==== PWM ====
+PWM controllers are sized based on the **maximum input power** they will ever see.
+One 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/)) A faster, cruder method is (panel wattage / 10) = charge controller amps.
+==== MPPT ====
+MPPT controllers are sized based on the **average power** they will see.
+The approach is different because
+  * MPPT are expensive
+  * MPPT can trim incoming power to avoid exceeding their output rating
+So MPPT controllers generally have [[electrical:solar:overpaneling|more panel put on them than their rating would suggest]] ("overpaneling").
+There are a few ways of calculating this.  The Victron MPPT calculator is quite good.  It will generally suggest 10-30% overpaneling.
+You can ballpark it manually by dividing *panel wattage / 14.25v((this appears to be the constant used in the Victron calculator))).  Example:
+''400w / 14.25v = 28.0702A''
+  * 28.0702 / 25A candidate = 3.0702A.  (3.0702A / 25A) = **12.28% overpaneled**.  On the lower end of Victron's overpaneling recommendation.
+  * 28.0702 / 20A candidate = 8.0702A.  (8.0702A / 20A) = **40.35% overpaneled**.  This exceeds Victron's overpaneling recommendation. 40% overpaneling might be fine at higher latitudes like Canada or Alaska, but the controller would be maxxed out quite often elsewhere.
+**Conclusion**:  25A is appropriate for  400w of panel.
+A? 20A?
+  - (28.0702A - 25A) =
 ===== overpaneling =====
 this section [[electrical:solar:overpaneling|has been moved]].
@@ Line 193: / Line 319: @@
 ==== 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 disconnects]] power relays (see below).
+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.
-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:
 ==== why loads aren't powered from LOAD terminals ====
@@ Line 230: / Line 354: @@
+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]].

RVwiki for vanfolk and others who live in vehicles

User Tools

Site Tools

Differences

Page Tools