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opinion:frater_secessus:self-heated_lifepo4

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opinion:frater_secessus:self-heated_lifepo4 [2023/09/03 16:11]
frater_secessus [TLDR] 		opinion:frater_secessus:self-heated_lifepo4 [2023/10/17 15:13] (current)
frater_secessus [how the approaches work]
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      * self-heated:   easier      * self-heated:   easier
      * DIY:  more control, more charging under certain conditions, usually cheaper      * 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)) 
 ===== how the approaches work ===== ===== how the approaches work =====
  
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   - sense ~freezing temps    - sense ~freezing temps 
   - shut off charging((normal BMS shutoff))   - shut off charging((normal BMS shutoff))
-  - allow 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+  - 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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   - use an external temperature controller and temperature probe   - use an external temperature controller and temperature probe
-  - turn a warming mat on/off with the controller+  - use the lowest-wattage warming mat practical for conditions((for gentlest, most-even heating)) 
 +  - and turn the mat on/off with the controller
  
 This means //warming happens whether or not charging is present//.  This may or may not be what you want.  This means //warming happens whether or not charging is present//.  This may or may not be what you want. 
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-With "soft" charging like a small solar setup it's a wash.  a matter of preference and cost.   +With "soft" charging like a small solar setup it's a wash.  a matter of preference and cost.   But in some specific use cases one approach might work better. 
  
  
-===== perfect storm for self-heated batteries =====+===== when self-heated might be preferable ===== 
 + 
 +When you want a packaged solution. 
 + 
 +If you run your bank very low habitually((stop doing that!)) and the warming load is enough to trigger BMS discharge shutdown.  This problem does not occur with self-heated because heating only runs when charging is present.  
 + 
 + 
 +===== when DIY warming might be preferable ===== 
 + 
 +==== robust charging ==== 
  
 With robust charging (alternator and/or bigger solar) there can be charging opportunities lost with self-heated batteries in freezing conditions.   With robust charging (alternator and/or bigger solar) there can be charging opportunities lost with self-heated batteries in freezing conditions.  
  
-Imagine +Imagine the following scenario
  
-* freezing overnights followed by a half-hour drive in the morning with a 30A DC-DC.  +  * freezing overnights followed by a half-hour drive in the morning with a 30A DC-DC.  
-* a battery with warming pad that consumed 60Wh overnight to stay above freezing, vs +  * a battery with warming pad that consumed 60Wh overnight to stay above freezing, vs 
-* a self-heating battery that is below freezing in the morning+  * a self-heating battery that is below freezing in the morning
  
 The externally warmed bank accepts current immediately and takes **15Ah of recharge**.  So after recouping the 60Wh used overnight it's **net +132Wh**. The externally warmed bank accepts current immediately and takes **15Ah of recharge**.  So after recouping the 60Wh used overnight it's **net +132Wh**.
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 With 50A charging it's 260Wh net vs 107Wh net. . With 50A charging it's 260Wh net vs 107Wh net. .
  
-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. 
 + 
 +==== specific configurations ====
  
 +You may want more control over the temperature setpoints.  
  
-===== perfect storm for DIY warming =====+Note from Secessus:  "since reading [[https://diysolarforum.com/threads/why-you-cannot-charge-lifepo4-below-0-degrees-celsius.2912/page-2#post-199774|this cell spec sheet data]] I keep my bank at toasty 50deg F."
  
  
-You run your bank very low habitually (don't do that) and the warming load is enough to trigger BMS discharge shutdown.   
  
 ===== how to think about the decision ===== ===== how to think about the decision =====
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   * how much charging would I miss out on because the bank is taking only 60w to run the heaters instead of taking everything I can throw at it?; and   * how much charging would I miss out on because the bank is taking only 60w to run the heaters instead of taking everything I can throw at it?; and
-   * how does this compare to the Wh required to keep the bank above freezing when no charging is present? +  * how does this compare to the Wh required to keep the bank above freezing when no charging is present? 
-   * 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?
  
 ===== further reading ===== ===== further reading =====
opinion/frater_secessus/self-heated_lifepo4.1693771900.txt.gz · Last modified: 2023/09/03 16:11 by frater_secessus

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