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opinion:frater_secessus:agm2lifepo4 [2023/12/28 12:08]
frater_secessus [Can I still use my existing DC-DC charger for alternator charging?] 		opinion:frater_secessus:agm2lifepo4 [2024/03/23 13:08]
frater_secessus [excess current]
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     * charging only above freezing 32F/0C     * charging only above freezing 32F/0C
   - what your existing charging system provides (or can be configured to provide).    - what your existing charging system provides (or can be configured to provide). 
 +    * alternator voltage and rating if a [[electrical:12v:alternator|combiner]] or [[electrical:12v:b2b|DC-DC]] is present
 +    * [[electrical:solar:charge_controller|solar charging]] (profiles, configurability, output rating,  protections if any)
 +    * [[electrical:converter|shore power charging]] (voltage, output rating, stages if any)
  
-If the existing system cannot be configured to meet LFP's needs then you are looking at replacing some components. For more specific guidance please share details about your setup, use case, budget, and priorities. +If the existing system cannot be configured to meet LFP's needs within [[electrical:12v:alternator_details#current|the  alternator's comfort zone]] then you are looking at replacing some components. For more specific guidance please share details about your setup, use case, budget, and priorities. 
  
 Note:  **undercharging lithium is not an issue** unless you are running out of power. This is a radical change from lead-battery charging.  Note:  **undercharging lithium is not an issue** unless you are running out of power. This is a radical change from lead-battery charging. 
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 ==== Will I need a special LFP solar charge controller? ==== ==== Will I need a special LFP solar charge controller? ====
  
-Probably not, assuming your existing [[electrical:solar:charge_controller|controller]] has a profile that meet's the LFP's stated needs, or has [[electrical:solar:charge_controller_setpoints|configurable setpoints]].    +Probably not, assuming your existing [[electrical:solar:charge_controller|controller]] has a profile that meet's the LFP's stated needs, or has [[electrical:solar:charge_controller_setpoints|configurable setpoints]] that you can adjust to meet needs. 
  
  
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 Some controllers do use temperature sensing to cut off lithium charging near the freezing point.  Some only do this in the preconfigured Lithium profiles (Renogy, on supported models).   Some controllers do use temperature sensing to cut off lithium charging near the freezing point.  Some only do this in the preconfigured Lithium profiles (Renogy, on supported models).  
  
-Note that having a temp probe left over from lead battery charging does not mean low-temp cutoff is supported in the controller.  With lead banks temp sensing is used to adjust charging voltage for conditions, not turn off charging in freezing weather.((lead batts actually thrive on charging in freezing temps since higher SoC means it takes deep cold to freeze them solid))+Note that having a temp probe left over from lead battery charging does not mean low-temp cutoff is supported in the controller.  With lead banks temp sensing is used to adjust charging voltage to battery temperature((higher voltage when cold, lower voltage when hot)) and are not intended to turn off charging in freezing weather.((lead batts actually thrive on charging in freezing temps since higher SoC means it takes deep cold to freeze them solid))  Read your controller docs to see if the temp probe can be used to sense freezing temps with Li banks.  
 + 
 +In addition, some batteries have a low temperature charging disconnect built into the BMS, or internal [[opinion:frater_secessus:self-heated_lifepo4|heating to skirt the issue]].  The owner can also [[https://diysolarforum.com/threads/lifepo4-heating-pad-for-cold-temperatures.5/page-26|add external warming]].  
 ===== alternator charging ===== ===== alternator charging =====
  
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   * 1.0C - typical limit enforced by BMS   * 1.0C - typical limit enforced by BMS
  
-From the battery's point of view, alternator charging rates should probably be ≤0.5C, with 0.4C probably being the sweet spot.  So ≤80A for a 200Ah bank.  From the alternator's point of view, current should be limited to [[electrical:12v:alternator_details#current|what the alternator can comfortably provide]] under expected charging conditions.  +From the battery's point of view, alternator charging rates should be ≤0.5C, with 0.4C likely being the sweet spot.  So ≤80A for a 200Ah bank.  From the alternator's point of view, current should be no greater than [[electrical:12v:alternator_details#current|the alternator can comfortably provide]] under expected charging conditions.  
  
 As the Battle Born quote above suggests, for average LFP banks and average cargo van alternators these criteria will often be met with no reconfiguration.  If the criteria cannot be met then we will need [[electrical:12v:b2b|DC-DC charging]] or some other approach to manipulate voltage and/or current.((diode-based isolator, dedicated second alternator, etc)) As the Battle Born quote above suggests, for average LFP banks and average cargo van alternators these criteria will often be met with no reconfiguration.  If the criteria cannot be met then we will need [[electrical:12v:b2b|DC-DC charging]] or some other approach to manipulate voltage and/or current.((diode-based isolator, dedicated second alternator, etc))
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-[Note from secessus:  there is [[https://diysolarforum.com/threads/why-you-cannot-charge-lifepo4-below-0-degrees-celsius.2912/post-199774|some evidence]] that LiFePO4 fares better when cell temps are held to warming temps than just above freezing.  For this reason I warm my bank to 50F.]+[Note from secessus:  there is [[https://diysolarforum.com/threads/why-you-cannot-charge-lifepo4-below-0-degrees-celsius.2912/post-199774|some evidence]] that LiFePO4 fares better when cell temps are held to warmer temps than just above freezing.  For this reason I warm my bank to 50F.]
opinion/frater_secessus/agm2lifepo4.txt · Last modified: 2024/03/23 13:13 by frater_secessus

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