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--- electrical:12v:drop-in_lifepo4 [2022/09/14 15:24]
frater_secessus [myth: you must use DC-DC for alternator charging Li]
+++ electrical:12v:drop-in_lifepo4 [2022/10/18 12:13]
frater_secessus [myth: you must use DC-DC for alternator charging Li]
@@ Line 186: / Line 186: @@
 Overcharging lithium to run the cell balancers is like driving up to every red light at 100mph in order to trigger the ABS.  It's //causing// the problem in order to //solve// the problem.
+==== myth:  lithium doesn't need absorption ====
+Lithium doesn't need Absorption [[electrical:12v:charging#absorption_stage|in the way lead does]].  In some circumstances, however, an Absorption duration can help match [[electrical:solar:charge_controller_setpoints|charging setpoint]] expectations to [[electrical:depth_of_discharge|state of charge]] reality.
+Most charts and tables showing voltage v. SoC assume moderate rates of charge like 0.2[[electrical:12v:battery_capacity|C]] (20A per 100Ah of capacity).  At that rate the charts are reasonably accurate.
+**Very high charge rates**, as sometimes seen with [[electrical:12v:drop-in_lifepo4#mythyou_must_use_dc-dc_for_alternator_charging_li|alternator charging]] or large [[electrical:converter|shore power chargers]], can throw off these chart estimates. 0.8C charging might only yield 80% SoC when one expected 90%. Conversely, **very low charge rates** may result in unintentional overcharge;  98% instead of 90%.
+One rule of thumb is that the bank is fully charged when you are at your target voltage and current acceptance has decreased to ≤0.10C.
+Further reading:  [[https://www.youtube.com/results?search_query=offgrid+garage+absorption|Off-grid Garage videos]] testing various absorption approaches
 ==== myth:  you can't charge Li with a lead battery charger ====
@@ Line 249: / Line 260: @@
 === testing your isolator with Li ===
-Here an order of operations one might use to assess whether or not isolator charging will work in a given install:((discontinue at once if you observe unacceptable results, and consider DC-DC or increasing solar)):
+see [[electrical:12v:directcharginglfp#assessing_your_setup_for_direct_alternator_charging|this section]]
-  - if the isolator is already in use with lead-chemistry banks before the upgrade, //pay attention to the voltage and current at which the existing bank is being charged//.  This is your baseline for alternator charging. Ah-for-Ah lithium will likely draw more current than lead, but Li banks are typically lower in Ah than the lead banks they replace as DoD can be lower.((Lithium requires about 0.62 as much Ah as lead for the same amount of //usable// capacity.))
-  - Read and understand your Li battery manufacturer's charging specs - undercharging is fine((assuming one stays above 20% State of Charge)); overcharging is less so but is relatively rare in an isolator context.
-  - Read and understand your alternator's specs
-  - Read and understand your isolator's specs and functionality
-  - observe your vehicle's chassis voltage during normal operation - note that the voltage //at the battery's location// will likely be lower due to long wiring and also lower when the wiring is carrying a hefty charging current.
-  - make a first approximation about the ability of alternator, your isolator, and your Li battery to cooperate
-  - install [[electrical:12v:battery_monitor|a battery monitor]] so you can observe current and voltage at the battery.  Or use the battery's own BT access.
-  - ensure the fuse between your chassis and battery bank is sized so //you cannot draw more than the alternator and wiring can handle//
-  - make the first test run a brief one and with the Li fairly well charged.((higher states of charge will typically lessen current demands to some degree))((if you have paralleled batteries you might want to do this step with just one in place to get a feel for the draw.))  Start the engine and see if the charging current and voltage is acceptable.  Turn off the engine.
-  - test it with a drive.
-  - repeat the last two steps with the Li bank at lower and lower states of charge, down to the lowest expected state of charge you expect to recharge from alternator.
-**Caveats**:
-  * Only alternator charge while driving ([[rv:idling|no idling]] except for brief preliminary test).
-  * Pay attention while charging from alternator to keep from overcharging the Li or holding for long periods at high [[electrical:depth_of_discharge|states of charge]].
-  * You may want a manual disconnect or [[electrical:12v:alternator_charging_hvd|HVD]] to shut off alternator charging due to excess voltage or if the bank is already charged.  These can be added on the D+ wire (ignition triggered) or electronics ground wire (VSR, solenoid, or voltage-triggered DC-DC)
 === but that Victron video! ===
-Why would a manufacturer of pricey [[electrical:12v:b2b|DC-DC chargers]] want to publish [[https://www.youtube.com/watch?v=jgoIocPgOug|a video]] of an LFP pack smoking an alternator?((7:01))  And why would they turn comments off?  Oh, right.
+Why would a manufacturer of pricey [[electrical:12v:b2b|DC-DC chargers]] want to publish [[https://www.youtube.com/watch?v=jgoIocPgOug|a video]] of a big LFP pack smoking a car alternator?((7:01))  And why would they turn comments off?  Oh, right.
 The setup:
@@ Line 305: / Line 297: @@
-I would very much like to have seen the regular alt and all <del>three</del> four workarounds demonstrated //at the same RPM settings//.
+{ I would very much like to have seen the regular alt and all <del>three</del> four workarounds demonstrated //at the same RPM settings//.  -- secessus }

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