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opinion:frater_secessus:self-heated_lifepo4

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opinion:frater_secessus:self-heated_lifepo4 [2025/06/24 18:36]
frater_secessus [charging cutoff] 		opinion:frater_secessus:self-heated_lifepo4 [2026/10/03 20:07] (current)
frater_secessus [Self-heated vs DIY warming]
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 DRAFT DRAFT
  
-====== Self-heated vs DIY warming ======+====== LiFePO4 charging and freezing temps:  self-heated vs DIY warming approaches ======
  
 ===== TLDR ===== ===== TLDR =====
  
-  * LiFePO4 cannot be charged when the cells are below ~freezing, or discharged well below freezing +  * LiFePO4 cannot be charged when the cells are below ~freezing, or even discharged at substantially lower temps.  
-  * some kind of warming is required before charging+  * therefore when cells are at ~freezing temps some kind of warming is required before charging
      * self-heated:   easier      * self-heated:   easier
-     * DIY:  more control, more charging under certain conditions, usually cheaper +     * externally-heated (usually DIY):  more control, more charging under certain conditions, usually cheaper 
-  * in practice, warming is combined with other forms of protection:  BMS low temp charging shutoff, solar or DC-DC low temp charging cutoff, etc.(("belt and suspenders" approach)) +  * in practice, warming is combined with other forms of protection:  [[electrical:12v:drop-in_lifepo4#bms_features_and_specs|BMS low temp cutoffs]], solar or DC-DC low temp charging cutoff, etc.(("belt and suspenders" approach)) 
 ===== how the approaches work ===== ===== how the approaches work =====
  
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-=== backing into a minimum temperature setpoint ===+==== backing into a minimum temperature setpoint ====
  
-There are a couple steps here:  reading your cell data sheet, and assessing your maximum charging current ([[electrical:12v:battery_capacity|C]]) rate.+There are two pieces of information needed here:  a datasheet for your cells, and a realistic assessment of your maximum charging current ([[electrical:12v:battery_capacity|C rate]]) under best possible conditions.
  
-== what the datasheet tells us ==+=== what the datasheet tells us ===
  
 The cells inside [[electrical:12v:drop-in_lifepo4|your LFP]] are made of individual cells.  These cells are usually made by a big cell manufacturer, who publish datasheets related to those cells.  You may have to google to find out the actual cells inside your battery, or watch a teardown video.  Then you can google to find the datasheet for those cells.   The cells inside [[electrical:12v:drop-in_lifepo4|your LFP]] are made of individual cells.  These cells are usually made by a big cell manufacturer, who publish datasheets related to those cells.  You may have to google to find out the actual cells inside your battery, or watch a teardown video.  Then you can google to find the datasheet for those cells.  
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 ^    ^   ^ ^    ^   ^
-| a  |   | +| Temp (T)   | Charge rate (C) | 
-|    |   | +| <0°C | No charging allowed      | 
-|    |   | +| 0°C  T <10°C | 0.1C charge to 80% SOC   |    
-|    |   | +| 10°C  T <15°C | 0.2C   |    
-|    |   | +| 15°C  T <45°C | 0.5C   |    
-|    |   | +| 45°C  T <55°C | 0.2C  |    
-|    |   |+| >55°C | No charging allowed   |   
  
  
 +=== C rate at full charging power ===
  
 +In secessus' use case his charging can  max out at ~55A((and usually much lower)) with solar and alternator combined.  55A/280Ah = ~**0.2C**.
  
-Temp (T) | Charge rate (C) +=== putting it all together ===
----|--- +
-<0°C | No charging allowed +
-0°C  T <10°C | 0.1C charge to 80% SOC +
-10°C  T <15°C | 0.2C +
-15°C  T <45°C | 0.5C +
-45°C  T <55°C | 0.2C +
->55°C | No charging allowed +
- +
- +
- +
- +
-== C rate at full charging power == +
- +
- +
- +
- +
-== putting it all together == +
- +
- +
-These are used in a battery where the recommended constant charge rate is ≤0.5[C](https://rvwiki.mousetrap.net/doku.php?id=electrical:12v:battery_capacity).  That amount of current is only acceptable when temps are 15°C  T <45°C.  So in my case if I want to charge at 0.5C I need to keep the bank at least 15°C (~60°F).   In practice I only have ~0.33C of charging grunt so I only need to hold 10°/50°F. +
  
 +Because his charge rate can reach **0.2C** he chose a warming setpoint of **10°C (50°F)**.
  
  
opinion/frater_secessus/self-heated_lifepo4.1750790160.txt.gz · Last modified: 2025/12/24 22:52 (external edit)

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