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electrical:12v:lifepo4_batteries_thread [2017/12/09 17:52]
frater_secessus
electrical:12v:lifepo4_batteries_thread [2023/10/20 13:48] (current)
princess_fluffypants [stress on charging equipment]
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 ====== Synopsis of C&S LiFePO4 batteries thread ====== ====== Synopsis of C&S LiFePO4 batteries thread ======
-The Cruisers and Sailing forum has a 300+ page [[http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html|LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks]] thread.  +This page is primarily for people interested in making their own lithium battery banks. This means buying raw cells (usually at a deep discount directly from a factory in China), and then putting together your own bank want with your own bus bars, chargers, Battery Monitoring System (BMS), and potentially things like bluetooth controllers and heaters. 
 + 
 +The advantage is potentially //massive// capacities for lower costs when compared to battery bank of [[electrical:12v:drop-in_lifepo4|drop-in lithium]] batteries. Going DIY also gives additional options in terms of different voltages and shapes of packs, which can be helpful for fitting them into weird places on RVs and vans. 
 + 
 +This is a fairly technical endeavor with a not insignificant risk of fire/explosion if you screw it up, so doing a lot of research beforehand is highly recommended.  And good place to start is the Cruisers and Sailing forum, which has a 300+ page [[http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069.html|LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks]] thread.  
  
 There is gold in the thread but it can be hard to find.  This page attempts to distill the thread down to best practices for RV/campervan use of LiFePO4 batteries.  Links are provided so readers can go back to the thread for context-checking and critical examination. There is gold in the thread but it can be hard to find.  This page attempts to distill the thread down to best practices for RV/campervan use of LiFePO4 batteries.  Links are provided so readers can go back to the thread for context-checking and critical examination.
  
 +Another excellent resource is the [[https://diysolarforum.com/|DIY Solar Power forum]].
  
 ===== Suitability for RV use ===== ===== Suitability for RV use =====
  
 LiFePO4  LiFePO4 
-  * can take full current during charging;  there are no //stages// in the lead-acid sense+  * can take full current during charging;  there are no //stages// in the lead-acid sense(([[https://img.mousetrap.net/misc/lithiumAbsorpTimes.jpg|higher charge rates can make a quasi-absorption useful]] to replace all the amps))
   * can use more nominal capacity than lead-acid (80-90% v. 50% [[electrical:depth_of_discharge|depth of discharge]])   * can use more nominal capacity than lead-acid (80-90% v. 50% [[electrical:depth_of_discharge|depth of discharge]])
-  * are not damaged by low SoC+  * are not damaged by [[electrical:12v:psoc|partial stage of charge]]
   * can be mounted vertically or on a thin edge (but not flat)((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-234.html#post1452743))   * can be mounted vertically or on a thin edge (but not flat)((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-234.html#post1452743))
   * smaller and lighter than like-capacity LA   * smaller and lighter than like-capacity LA
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 ==== LiFePO4 charging for RVs: running barefoot ==== ==== LiFePO4 charging for RVs: running barefoot ====
  
-Although his setup does not use it, T1 Terry describes a "middle 80%" approach that works well with Fractional C systems. It can eliminate the need for [[electrical:12v:BMS|BMS]] balancing+T1 Terry describes a gentle, relatively low-tech approach that can work well with vandweller use patterns It does not use a [[electrical:12v:BMS|BMS]], judging that in a vandwellers' use the BMS introduces more hazards than it alleviates.  This approach: 
-  * starts with a balanced battery when installing.+ 
 +  * starts with a balanced battery
   * uses moderate terminal voltage (13.8v) to gently rebalance cells((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-77.html#post1132126)),((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-44.html#post1096480)), and even become more balanced over time.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-109.html#post1142675))  If they do get out of balance for some reason, run more conservative SoC voltages until they can be manually rebalanced.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-294.html#post1779359))   * uses moderate terminal voltage (13.8v) to gently rebalance cells((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-77.html#post1132126)),((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-44.html#post1096480)), and even become more balanced over time.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-109.html#post1142675))  If they do get out of balance for some reason, run more conservative SoC voltages until they can be manually rebalanced.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-294.html#post1779359))
-  * charges at less than 1C, common in solar charging+  * charges and discharges at less than [[electrical:12v:battery_capacity|1C]], common in solar charging.  i.e. less than 100A with a 100Ah bank. 
   * keeps the voltage "between the [voltage] knees", 13.8v - 11.8v.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-103.html#post1140470))  This is also called the "middle 80%".   * keeps the voltage "between the [voltage] knees", 13.8v - 11.8v.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-103.html#post1140470))  This is also called the "middle 80%".
-  * does not //require// strapping((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-59.html#post1118000)) although it is a recommended best practice((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-253.html#post1574064)) +  * does not require strapping((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-59.html#post1118000)) although it is a recommended best practice((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-253.html#post1574064)) 
-  * no BMS required ("running barefoot")+
  
 Since the defining feature of this approach is the lack of BMS, it will be referred to as "barefoot" on this page.  Since the defining feature of this approach is the lack of BMS, it will be referred to as "barefoot" on this page. 
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 ==== LiFePO4 characteristics ==== ==== LiFePO4 characteristics ====
  
-LiFePO4 are fully charged at 13.6v (3.4v/cell).((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-43.html#post1069816)) Voltage rises very quickly after LiFePO4 are fully charged (faster than the internal temps rise) so voltage can be used to assess full charge.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-45.html#post1096611))+LiFePO4 (Lithium-Iron-Phosphate) are fully charged at 13.6v (3.4v/cell).((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-43.html#post1069816)) Voltage rises very quickly after LiFePO4 are fully charged (faster than the internal temps rise) so voltage can be used to assess full charge.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-45.html#post1096611))
  
 There is anecdotal evidence that sustained Vfloat at 13.8v (3.45v/cell) for months may not affect capacity.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-160.html#post1187410)) There is anecdotal evidence that sustained Vfloat at 13.8v (3.45v/cell) for months may not affect capacity.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-160.html#post1187410))
  
-LiFePO4 cells have a markedly lower full charge voltage than LiPo which is 3.7v.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-91.html#post1136613))  The LFP gives up energy density for stability and safety.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-93.html#post1137602))+LiFePO4 cells have a markedly lower full charge voltage than LiPo (Lithium-Polymer) or LiIon (Lithium-Ion) which is 3.7v.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-91.html#post1136613))  The LFP gives up energy density for stability and safety.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-93.html#post1137602))
  
 Rated cycles will be easier to attain by going no lower than 80% DoD, 12.4v (3.10v/cell).((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-56.html#post1113745)) Shallower cycling may increase both cycles and lifetime capacity.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-175.html#post1207749)),((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-177.html#post1231923)) Rated cycles will be easier to attain by going no lower than 80% DoD, 12.4v (3.10v/cell).((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-56.html#post1113745)) Shallower cycling may increase both cycles and lifetime capacity.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-175.html#post1207749)),((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-177.html#post1231923))
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 Increased alternator load may also cause premature destruction of belts((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-175.html#post1220483)) or throwing a belt off the pulley.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-176.html#post1220970)) Increased alternator load may also cause premature destruction of belts((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-175.html#post1220483)) or throwing a belt off the pulley.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-176.html#post1220970))
  
 +For this reason, if you are charging large (200ah+) lithium batteries directly off of a vehicle alternator it is generally recommended to use a [[electrical:12v:b2b|DC/DC charger]] to help moderate and control the amount of amps being put into the battery.
 ===== banding ===== ===== banding =====
 Banding (physical binding of cells to prevent expansion) may not be necessary in RVs: Banding (physical binding of cells to prevent expansion) may not be necessary in RVs:
electrical/12v/lifepo4_batteries_thread.1512859971.txt.gz · Last modified: 2020/10/11 19:48 (external edit)