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opinion:frater_secessus:self-heated_lifepo4 [2025/06/24 18:49]
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 ===
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 | 10°C  T <15°C | 0.2C   |    | 10°C  T <15°C | 0.2C   |   
 | 15°C  T <45°C | 0.5C   |    | 15°C  T <45°C | 0.5C   |   
-|  45°C  T <55°C | 0.2C  |   +| 45°C  T <55°C | 0.2C  |   
 | >55°C | No charging allowed   |    | >55°C | No charging allowed   |   
  
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 === C rate at full charging power === === C rate at full charging power ===
  
-In secessus' use case his charging can  max out at ~55A((and usually much lower)).  55A/280Ah = ~**0.2C**.+In secessus' use case his charging can  max out at ~55A((and usually much lower)) with solar and alternator combined.  55A/280Ah = ~**0.2C**.
  
 === putting it all together === === putting it all together ===
  
-Because his charge rate can reach **0.2C** he chose a warming setpoing of **10°C (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_lifepo4.1750790943.txt.gz · Last modified: 2025/12/24 22:52 (external edit)