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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] 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. |
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| 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. |
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| 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. |
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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. |
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| Another excellent resource is the [[https://diysolarforum.com/|DIY Solar Power forum]]. |
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===== Suitability for RV use ===== | ===== Suitability for RV use ===== |
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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 |
==== LiFePO4 charging for RVs: running barefoot ==== | ==== LiFePO4 charging for RVs: running barefoot ==== |
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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") | |
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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. |
==== LiFePO4 characteristics ==== | ==== LiFePO4 characteristics ==== |
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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)) |
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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)) |
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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)) |
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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)) |
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)) |
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| 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: |