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opinion:frater_secessus:self-heated_lifepo4 [2023/09/03 16:29]
frater_secessus [when it's a wash] 		opinion:frater_secessus:self-heated_lifepo4 [2024/11/24 16:28] (current)
frater_secessus [robust charging] added blog post
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 ===== TLDR ===== ===== TLDR =====
  
-  * LiFePO4 cannot be charged when the cells are below ~freezing.+  * LiFePO4 cannot be charged when the cells are below ~freezing, or discharged well below freezing
   * some kind of warming is required before charging   * some kind of warming is required before charging
      * self-heated:   easier      * self-heated:   easier
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   - allow incoming power only to the internal heaters, typically ~60w   - allow incoming power only to the internal heaters, typically ~60w
   - when cell temps are >freezing charging is re-enabled   - when cell temps are >freezing charging is re-enabled
-  - optional:  heating may continue until some warmer setpoint, typically ~50F when this feature is utilized+  - optional:  heating may continue until some warmer setpoint is reached, typically 40F-50F when this feature is utilized
  
 This means //warming only happens when charging is present//.  This may or may not be what you want.  This means //warming only happens when charging is present//.  This may or may not be what you want. 
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 If one was charging by alternator only and only driving to/from work while stealthing in freezing weather it's conceivable the self-heated batt would get //never get charged at all// because it wouldn't have time to get out of the heating phase. If one was charging by alternator only and only driving to/from work while stealthing in freezing weather it's conceivable the self-heated batt would get //never get charged at all// because it wouldn't have time to get out of the heating phase.
  
 +[Note:  those who want to charge vigorously might want to [[https://mouse.mousetrap.net/blog/2024-11-23-backchannel--charging-rates-and-self-heating-batteries-.html#temperature-and-charge-rate|keep the battery bank quite warm]]]
 ==== specific configurations ==== ==== specific configurations ====
  
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   * do I need greater configurability than the built-in heater allows?   * do I need greater configurability than the built-in heater allows?
   * do I have the interest or ability to DIY?   * do I have the interest or ability to DIY?
 +
 +===== DIYing a solution =====
 +
 +DIY solutions include warming and/or charging cutoff.  Multiple approaches can be combined into a "belt and suspenders" solution.  
 +
 +
 +==== warming ====
 +
 +
 +If your preferred battery has everything but heating you might want to [[https://diysolarforum.com/threads/lifepo4-heating-pad-for-cold-temperatures.5/page-26|DIY a heater]].  It is typically cheaper than built-in heat and offers more control.  It typically involves:
 +
 +  - a [[https://amzn.to/4d5MFii|low-wattage warming pad]], as one finds for reptile pets, animal comfort pads, etc.  [[https://amzn.to/4e1KGww|RV tank heating pads]] will work but the wattage is much higher (60w?) and might result in less even heating or overheating. Higher wattages will be required in colder areas.
 +  - a [[electrical:temperature_control|temperature controller]] to turn the warming off and on at a given temp ([[https://amzn.to/3zjubNp|examples]])
 +
 +Both pads and controllers are available in 12vdc and 120vac. In moderate climates the bank can likely just sit on a mat.  Colder conditions might require pads adhered to all sides, and/or insulating the batter.  
 +
 +
 +
 +
 +
 +
 +
 +
 +
 +==== charging cutoff ====
 +
 +
 +
 +
 +=== internal charge cutoff ===
 +
 +It is very common for BMS to have a charging cutoff feature that engages near freezing.  Some will allow you to adjust the cutoff setpoint in an app. 
 +
 +If the BMS lacks cutoff feature (or lacks configurability and you want to disable at a higher temp) see below.
 +
 +
 +=== external charge cutoff ===
 +
 +It may be possible to disable charging externally but //all charging sources// must be considered, and must have a temp probe or other way to measure bank temperature.
 +
 +Some [[electrical:solar:charge_controller|solar charge controllers]] have configurable setpoints to stop charging at a given temp.  
 +
 +Chargers which lack cutoff but can be switched OFF/ON can be controlled by a signal from a thermal switch (nonconfigurable) or temp controller (configurable).  In this approach the switch or probe is attached to the bank.  Below a given temperature the control circuit is disrupted and the charger turns off. 
 +
 +
  
 ===== further reading ===== ===== further reading =====
opinion/frater_secessus/self-heated_lifepo4.1693772948.txt.gz ยท Last modified: 2023/09/03 16:29 by frater_secessus

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