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electrical:12v:drop-in_lifepo4 [2024/12/31 17:50]
frater_secessus [myth: floating will cause microcycling] 		electrical:12v:drop-in_lifepo4 [2025/05/04 14:19] (current)
frater_secessus [drawbacks of lithium]
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 ===== drawbacks of lithium ===== ===== drawbacks of lithium =====
  
-  * Li is relatively expensive up front+  * Li has (historically at least) been relatively expensive up front.  Prices started plummeting somewhere around 2024.
   * Li cells need a [[#bms_functions|BMS]] to protect them from damage.((some DIYers run Li "barefoot" (without a BMS) )) For example, Li can be damaged by overvoltage, undervoltage, charging below freezing (32F), etc.  Some batteries have low-temp cutoff and/or internal heating to address the cold-charging limitation.  Most Drop-in Lithium batteries will have a BMS integrated into them, but raw cells do not.   * Li cells need a [[#bms_functions|BMS]] to protect them from damage.((some DIYers run Li "barefoot" (without a BMS) )) For example, Li can be damaged by overvoltage, undervoltage, charging below freezing (32F), etc.  Some batteries have low-temp cutoff and/or internal heating to address the cold-charging limitation.  Most Drop-in Lithium batteries will have a BMS integrated into them, but raw cells do not.
   * Li can be **damaged** by long duration at full charge or high voltage, or high ambient temperatures   * Li can be **damaged** by long duration at full charge or high voltage, or high ambient temperatures
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   - and think there's a problem so they won't start(("too smart for their own good"))   - and think there's a problem so they won't start(("too smart for their own good"))
  
-What we need is a //dumb// voltage source to get the party restarted.  The starter battery will do nicely.  +What we need is a //dumb// charging source to get the party restarted.  Another battery.  Power supply.  Charger with a "wake LiFePO4" mode, vehicle starter battery, etc.  
 + 
 +If you want to use the starter battery there are several possibilities:
  
   * Rigs with IGN-triggered relays can briefly turn the key to ACC then back off.((don't leave it on ACC long or the dead Li will suck power from the starter battery.  Either turn ACC off again or actually start the vehicle.))   * Rigs with IGN-triggered relays can briefly turn the key to ACC then back off.((don't leave it on ACC long or the dead Li will suck power from the starter battery.  Either turn ACC off again or actually start the vehicle.))
   * Rigs with voltage-sensing relays will have to actually start the engine or press a manual override switch to activate the VSR and wake the lithium bank.   * Rigs with voltage-sensing relays will have to actually start the engine or press a manual override switch to activate the VSR and wake the lithium bank.
   * Rigs with diode- or FET-based isolators would start the engine to spin the alternator and get power flowing through the isolator to the sleeping lithium   * Rigs with diode- or FET-based isolators would start the engine to spin the alternator and get power flowing through the isolator to the sleeping lithium
- +  * If you have no other options you can remove either the starter battery or house battery and locate them so a pair of jumper cables can connect them. 
  
  
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   * going into a period where you will need max capacity   * going into a period where you will need max capacity
   * to perform a capacity test   * to perform a capacity test
-  * to reset the BMS amp/SoC counter+  * to [[electrical:12v:battery_monitor#drift_and_reset|reset the BMS amp/SoC counter]]
   * to top-balance cells((to the degree this works))   * to top-balance cells((to the degree this works))
  
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   * **Absorption voltage** (Vabs) - whatever charging voltage your battery manufacturer recommends.((see the section on longevity in this article))   * **Absorption voltage** (Vabs) - whatever charging voltage your battery manufacturer recommends.((see the section on longevity in this article))
   * **Absorption duration** - whatever the battery manufacturer recommends, typically 0 to 20 minutes.((charging voltages ≥14.0v typically require no absorption duration at all))   * **Absorption duration** - whatever the battery manufacturer recommends, typically 0 to 20 minutes.((charging voltages ≥14.0v typically require no absorption duration at all))
-  * **Float voltage** (Vfloat) - Something like 13.4v((3.35vpc)) is a good compromise. See the discussion on float below.+  * **Float voltage** (Vfloat) - Something like 13.3v-13.4v((3.35vpc)) is a good compromise. See the discussion on float below.
   * **Absorption reconnect** - this voltage is the setpoint below which Absorption(("boost" in Renogy/EpEver nomenclature)) is restarted. Normally in a solar configuration Vfloat is held until sun goes down, solar conditions otherwise deteriorate, or a load is applied that is more than the solar can support.  Start with a value like 13.2v and see how your system behaves.  Adjust as needed.    * **Absorption reconnect** - this voltage is the setpoint below which Absorption(("boost" in Renogy/EpEver nomenclature)) is restarted. Normally in a solar configuration Vfloat is held until sun goes down, solar conditions otherwise deteriorate, or a load is applied that is more than the solar can support.  Start with a value like 13.2v and see how your system behaves.  Adjust as needed. 
   * **Equalize voltage** (Veq) - Li does not require equalization.  If it cannot be disabled in the controller it is common to set Veq the same as Vabs so it becomes a non-issue.((some folks who charge to lower voltages like 13.6v may use Veq to raise bank voltage into the 14s for various purposes.  See the section on longevity.))     * **Equalize voltage** (Veq) - Li does not require equalization.  If it cannot be disabled in the controller it is common to set Veq the same as Vabs so it becomes a non-issue.((some folks who charge to lower voltages like 13.6v may use Veq to raise bank voltage into the 14s for various purposes.  See the section on longevity.))  
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 ==== myth:  you must use DC-DC for alternator charging Li ==== ==== myth:  you must use DC-DC for alternator charging Li ====
  
-Depends on the battery, the alternator, the use case, and even the [[electrical:12v:alternator|combiner]].  For example, [[https://www.youtube.com/watch?v=VY2b71zoyvg|Battle Born says]] this about direct-charging lithium:+If you have been successfully charging an AGM bank through a relay then an LFP bank of similar rated capacity will likely charge similarly.  The actual results depend on the battery, the alternator, the use case, and even the [[electrical:12v:alternator|combiner]].   
 + 
 +[[https://www.youtube.com/watch?v=VY2b71zoyvg|Battle Born says]] this about direct-charging lithium:
  
 >> Yes, you can.  Under most circumstances you don't even need to modify your system. >> Yes, you can.  Under most circumstances you don't even need to modify your system.
  
-They do recommend [[electrical:12v:alternator#lithium-specific|a BIM]] or [[electrical:12v:b2b|DC-DC charger]] //for banks >300Ah//.+They do recommend [[electrical:12v:alternator#lithium-specific|a BIM]] or [[electrical:12v:b2b|DC-DC charger]] //for banks >300Ah//.   
 + 
 +If not already present, a small switch to [[electrical:12v:alternator#disabling_alternator_charging|disable the combiner]]((same goes for [[electrical:12v:b2b|DC-DC chargers]])) at will is a good idea. 
  
  
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   - Li doesn't like to be held at 100% State of Charge for long periods     - Li doesn't like to be held at 100% State of Charge for long periods  
-  - In practice a solar-charged bank doesn't bounce between Float and Absorption during the course of a day((unless a heavy enough load pulls Vbatt down to the re-Bulk setpoint).+  - In practice a solar-charged bank doesn't bounce between Float and Absorption during the course of a day((unless a heavy enough load pulls Vbatt down to the re-Bulk setpoint)).
  
 The 2nd point takes a bit of explaining.   A [[electrical:solar:charge_controller|solar charge controller]] completes Absorption then falls to into Float where it will remain as long as the sun((and system capacity)) cooperates.  Absorption //can// be re-triggered if voltage falls below the Absorption Reconnect setpoint, but that setpoint is even lower than Vfloat.  If that happens the solar charging has already been overtasked and we will get a "microcycle" during that day in any case if the sun comes back.   The 2nd point takes a bit of explaining.   A [[electrical:solar:charge_controller|solar charge controller]] completes Absorption then falls to into Float where it will remain as long as the sun((and system capacity)) cooperates.  Absorption //can// be re-triggered if voltage falls below the Absorption Reconnect setpoint, but that setpoint is even lower than Vfloat.  If that happens the solar charging has already been overtasked and we will get a "microcycle" during that day in any case if the sun comes back.  
electrical/12v/drop-in_lifepo4.1735667405.txt.gz · Last modified: 2024/12/31 17:50 by frater_secessus

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