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--- electrical:12v:drop-in_lifepo4 [2024/11/21 00:32]
frater_secessus [waking lithium batteries]
+++ electrical:12v:drop-in_lifepo4 [2025/03/18 13:27] (current)
frater_secessus [myth: you must use DC-DC for alternator charging Li]
@@ Line 300: / Line 300: @@
 Also see:  Will Prowse's  [[https://www.youtube.com/watch?v=Yf9N9zBgyB8|Lithium Battery Longevity: Double or Quadruple the Life of Your Lithium Battery]]
+===== waking lithium batteries =====
+Lithium banks can go dormant at low voltages in order to protect themselves:
+  - the BMS turns off the DISCHARGE channel to keep cell voltage from going any lower
+  - so the battery internally has ~11.0v or whatever but does not pass that voltage to the terminals on the outside of the battery case
+  - which means smart chargers don't see battery voltage
+  - and think there's a problem so they won't start(("too smart for their own good"))
+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 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
+  * 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.
@@ Line 333: / Line 360: @@
 | AGM        | 14.2v - 14.5v        | 14.4v                                                                                                               |
 | Flooded    | 14.4v - 14.8v        | 14.6v                                                                                                               |
-| LiFePO4    | 13.6v - 14.4v        | 14.0v((this is a matter of some debate.  LFP mfg charging recommendations are often [[opinion:frater_secessus:lifepo4_charging_voltage|quite high]] - secessus))  |
+| LiFePO4    | 13.6v - 14.4v        | 14.2v((this is a matter of some debate.  LFP mfg charging recommendations are often [[opinion:frater_secessus:lifepo4_charging_voltage|quite high]] - secessus))  |
@@ Line 439: / Line 466: @@
 ==== 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.
@@ Line 585: / Line 614: @@
   - 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
+  - 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.

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