| Both sides previous revision
Previous revision
Next revision
|
Previous revision
|
electrical:12v:lifepo4_batteries_thread [2017/12/09 17:49]
frater_secessus [Synopsis of C&S LiFePO4 batteries thread] |
electrical:12v:lifepo4_batteries_thread [2023/10/20 13:48] (current)
princess_fluffypants [stress on charging equipment] |
| |
| ====== 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 |
| |
| This can make LFP banks less complex and less expensive in an RV application. Assessing SOC by voltage is also more accurate with Fractional C charging/discharging than with high currents. | This can make LFP banks less complex and less expensive in an RV application. Assessing SOC by voltage is also more accurate with Fractional C charging/discharging than with high currents. |
| ==== LiFePO4 charging for RVs: Terrycharging ==== | ==== 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 | |
| | |
| | Since the defining feature of this approach is the lack of BMS, it will be referred to as "barefoot" on this page. |
| |
| For lack of a better term, this barefoot (no BMS)/ middle 80% / fractional-C approach will be called **Terrycharging** below. | |
| |
| ==== 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)) |
| | 16.80| 4.20|cell damage((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-93.html#post1137808)) | | | 16.80| 4.20|cell damage((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-93.html#post1137808)) | |
| | 14.40| 3.60|High Voltage Cutoff((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-109.html#post1142567)) | | | 14.40| 3.60|High Voltage Cutoff((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-109.html#post1142567)) | |
| | **13.80**| 3.45|**Terrycharging Vabs**, with gentle overcharge for balancing. Max safe non-BMS voltage.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-44.html#post1096480)) | | | **13.80**| 3.45|**barefoot Vabs**, with gentle overcharge for balancing. Max safe non-BMS voltage.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-44.html#post1096480)) | |
| | 13.60| 3.40|fully charged | | | 13.60| 3.40|fully charged | |
| | **13.40**| 3.35|**Terrycharging Vfloat** | | | **13.40**| 3.35|**barefoot Vfloat** | |
| | 13.25| 3.31|20% Depth of Discharge | | | 13.25| 3.31|20% Depth of Discharge | |
| | 12.80| 3.20|50% Depth of Discharge FIXME. Long-term storage.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-172.html#post1201146)) | | | 12.80| 3.20|50% Depth of Discharge FIXME. Long-term storage.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-172.html#post1201146)) | |
| | 12.40| 3.10|80% Depth of Discharge. Best for storage?((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-384.html#post2383574)) | | | 12.40| 3.10|80% Depth of Discharge. Best for storage?((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-384.html#post2383574)) | |
| | **11.80**| 2.95|**Terrycharging Low Voltage Disconnect**. Min safe non-BMS voltage. ((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-103.html#post1140470)) | | | **11.80**| 2.95|**barefoot Low Voltage Disconnect**. Min safe non-BMS voltage. ((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-103.html#post1140470)) | |
| | 11.20| 2.80|100% Depth of Discharge((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-104.html#post1140620)). Low Voltage Cutoff.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-109.html#post1142567)) | | | 11.20| 2.80|100% Depth of Discharge((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-104.html#post1140620)). Low Voltage Cutoff.((http://www.cruisersforum.com/forums/f14/lifepo4-batteries-discussion-thread-for-those-using-them-as-house-banks-65069-109.html#post1142567)) | |
| |
| 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: |
