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electrical:12v:alt_and_solar [2023/05/24 21:37]
frater_secessus [how alternator charging helps] 		electrical:12v:alt_and_solar [2025/08/23 22:14] (current)
frater_secessus [putting it all together]
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-Note:  although this page was written with alternator-augmented solar charging in mind, the general principles also apply to solar+[[electrical:shore_power|shore power charging]] and solar+[[electrical:generator|generator]] charging. +Note:  although this page was written with alternator-augmented solar charging in mind, the general principles also apply to solar+[[electrical:shore_power|shore power charging]] and solar+[[electrical:generator|generator]] charging. Also see [[electrical:12v:power_mix|Deciding on a Power Mix]]. 
 + 
 + 
 +> Solar and DC-DC alternator charging are going to be the best practices for maintaining charge in one's battery bank. It only requires a little math, a little discipline to stick with the math, and the right expectations about solar intake.  -- CMDR_Schrodinger((https://www.reddit.com/r/vandwellers/comments/15z8eh6/energy_management_during_trips/jxfv03f/))
  
  
-[[lifestyle:words_of_wisdom|Words of wisdom]]: "Bulk charging requires //current//. Absorption requires //relatively high voltage// and //time at that voltage//." - secessus 
  
 ====== Augmented solar charging ====== ====== Augmented solar charging ======
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 Solar works anytime there is available sunlight, not just when the vehicle is running.  Solar works anytime there is available sunlight, not just when the vehicle is running. 
  
-Alt charging alone is unlikely to get lead-acid chemistries fully charged since Absorption can take hours and alternators often cannot hold [[electrical:solar:charge_controller_setpoints|the required voltage]]. Incomplete charge ([[electrical:12v:psoc|Partial State of Charge]], or PSOC) over time will result in [[electrical:batterycide|battery murder]] of lead batts. +Solar can meet both the **voltage** and **time** requirements necessary for [[electrical:12v:charging|complete charging]];  this is critical with lead-acid chemistries which will otherwise suffer damage from [[electrical:12v:psoc|partial states of charge]].  
  
 How to avoid (or attenuate) battery murder with this scenario: How to avoid (or attenuate) battery murder with this scenario:
   * get access to shore power every couple of days to get the bank fully charged.  This will retard the murderification process; or   * get access to shore power every couple of days to get the bank fully charged.  This will retard the murderification process; or
   * use a different (and $$$) battery alternative like LiFePO4 (no problems with PSOC) or carbon foam (needs full charge every couple of weeks?); or   * use a different (and $$$) battery alternative like LiFePO4 (no problems with PSOC) or carbon foam (needs full charge every couple of weeks?); or
-  * add in a small amount of solar.  +  * add in a small amount of solar <-- what this article is about
  
  
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 From ~80% to 100% (Absorption stage) charging requires little current but a long time holding at a relatively high voltage.  So in our alt+solar scenario the alternator does the heavy lifting in the beginning then a small solar install does the light (but lengthy) work at the end.((The solar will also contribute during Bulk when the sun is shining.)) From ~80% to 100% (Absorption stage) charging requires little current but a long time holding at a relatively high voltage.  So in our alt+solar scenario the alternator does the heavy lifting in the beginning then a small solar install does the light (but lengthy) work at the end.((The solar will also contribute during Bulk when the sun is shining.))
  
-Having a bit of solar may mean you can us a simpler/cheaper isolator rather than a more $$ [[electrical:12v:b2b|DC-DC charger]]. +Having a bit of solar may mean you can use a simpler/cheaper combiner rather than a more $$ [[electrical:12v:b2b|DC-DC charger]].
  
 ===== how alternator charging helps ===== ===== how alternator charging helps =====
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 Alternator charging is extremely powerful and cheap compared to typical solar installs.  It works best when solar works worst:  when the batteries are deeply discharged in the morning.  The sun is weak then but the bank needs a large supply of current (early [[electrical:12v:charging#bulk_stage|Bulk charging]]).   Alternator charging is extremely powerful and cheap compared to typical solar installs.  It works best when solar works worst:  when the batteries are deeply discharged in the morning.  The sun is weak then but the bank needs a large supply of current (early [[electrical:12v:charging#bulk_stage|Bulk charging]]).  
  
-[[electrical:solar:charge_controller#pwm|PWM]] controllers are especially hamstrung in this scenario;  since they run the panels at battery voltage (Vbatt) they produce the least power exactly when the most power is required.  By the time alternator voltage (Valt) is reached PWM controllers are able to produce meaningful power.+[[electrical:solar:charge_controller#pwm|PWM]] controllers are [[electrical:solar:pwm_tweaking#pwm_s_achilles_heel|somewhat hamstrung in this scenario]];  because they run the panels ~at battery voltage((for the purposes of this discussion)) (Vbatt) they produce the least power exactly when the most power is required.  Pushing up bank voltage with the alt helps the PWM make more power.  
  
 Alt charging shovels current into the bank until Valt is reached, at which point it begins to taper off.  Solar can take it from there.  A good metaphor might be a two-stage rocket:  the alternator does the heavy lift getting the rocket off the ground then the solar charging takes care of the high altitude, high speed duties.  Alt charging shovels current into the bank until Valt is reached, at which point it begins to taper off.  Solar can take it from there.  A good metaphor might be a two-stage rocket:  the alternator does the heavy lift getting the rocket off the ground then the solar charging takes care of the high altitude, high speed duties. 
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 > Use a generator or alternator to get to 85% SOC or so early in the AM, then let Solar spend all day polishing off the last 15% because that takes time more than amps. - a64pilot((https://www.cruisersforum.com/forums/f14/time-it-takes-to-fully-charge-batteries-238875-9.html#post3223983)) > Use a generator or alternator to get to 85% SOC or so early in the AM, then let Solar spend all day polishing off the last 15% because that takes time more than amps. - a64pilot((https://www.cruisersforum.com/forums/f14/time-it-takes-to-fully-charge-batteries-238875-9.html#post3223983))
  
 +
 +The alternator can help meet [[electrical:12v:charging#charging_current|lead bank minimum charging current requirements]].  
 ===== optimal alternator contribution ===== ===== optimal alternator contribution =====
  
-Broadly speaking, //alternator charging is most effective in the morning// and //solar charging is most effective later in the day//.  +Note:  this section talks about alternator contribution but also applies to generators.  
 + 
 +Broadly speaking, //alternator charging are most effective in the morning// and //solar charging is most effective at local solar noon//.  This pattern is most evident when using isolators/relays and/or lead chemistry batteries, and less evident when using [[electrical:12v:b2b|DC-DC chargers]] and/or lithium chemistries.
  
 There are several factors in play here.   There are several factors in play here.  
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 ==== putting it all together ==== ==== putting it all together ====
  
-Alternator((or generator)) charging is most helpful/efficient((Ah replaced for a  given amount of engine runtime)) in the morning when the bank voltage and state of charge are lowest.  This may mean shifting driving errands to mornings or rainy days.+Alternator (or generator) charging is most helpful/efficient((Ah replaced for a  given amount of engine runtime)) in the morning when the bank voltage and state of charge are lowest.  This may mean shifting driving errands to mornings or rainy days.
  
  
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   - the Li voltage curve is very flat in the middle, so the voltage delta will be stable through the "middle 80%"   - the Li voltage curve is very flat in the middle, so the voltage delta will be stable through the "middle 80%"
-  - for average users, Li will not have an Absorption stage in the lead-chemistry sense.((advanced users may find [[electrical:12v:electrical:12v:drop-in_lifepo4#mythlithium_doesn_t_need_absorption|exceptions]] to this general statement))+  - for average users, Li will not have an Absorption stage in the lead-chemistry sense.((advanced users may find [[electrical:12v:drop-in_lifepo4#mythlithium_doesn_t_need_absorption|exceptions]] to this general statement))
   - Lithium is often charged with DC-DC, which charges at the ~same voltage as solar   - Lithium is often charged with DC-DC, which charges at the ~same voltage as solar
  
electrical/12v/alt_and_solar.1684964240.txt.gz · Last modified: 2023/05/24 21:37 by frater_secessus

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