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--- electrical:12v:alternator [2024/03/02 19:14]
frater_secessus [paralleling different chemistries]
+++ electrical:12v:alternator [2024/04/05 11:05]
frater_secessus [gotchas]
@@ Line 159: / Line 159: @@
   * **charging**:  both batteries will charge to 14.2v (given enough time)
-  * **no charging:  relay separates ("isolates") the batteries.  Starter batt rests at 12.7v and lithium at 13.5v.
+  * **no charging**:  relay separates ("isolates") the batteries.  Starter batt rests at 12.7v and lithium at 13.5v.
@@ Line 193: / Line 193: @@
 "Split charge relay (SCR)", "split charger", "automatic charge relay (ACR)", "Voltage sensing relay (VSR)", solenoid, relay, etc.
-Power from the alternator is shared with the house battery by paralleling the two sets of batteries at certain times. This allows the [[electrical:12v:intro|house battery]] to charge but does not allow the house battery to pull power from the starter battery when not combined.
+Power from the alternator is shared with the house battery by paralleling the two sets of batteries at certain times. This allows the [[electrical:12v:intro|house battery]] to charge but does not allow the house battery to pull power from the starter battery when not combined.  [[https://www.youtube.com/shorts/nHS7aJuJd6c|This short video]] illustrates how it works.
@@ Line 477: / Line 477: @@
 Reasonable charging rates can also be easier on the alternator when charging suddenly stops, whether by completion((same reason headlights are turned on at the donor car when jumpstarting)) or BMS intervention. Blue Sea makes an [[https://www.bluesea.com/resources/91|alternator field disconnect]] which shuts down alternator power just before disconnecting the load, but this may be chiefly applicable to marine alternators.  Others have discussed installing a small lead-acid battery parallel to the Li bank;  in theory this could soften the blow from Li leaving the circuit.  Other sources suggest the presence of the starter battery would be sufficient.((https://shop.pkys.com/Alternator-Lithium-Battery.html))
+==== harvest ====
+Ah = Amps x hours.  If your combiner averages 30A and you drive for 1.5 hours it can replace 45Ah (30A x 1.5 hours).
+Note:  the current produced by direct charging vs DC-DC charging is different.
+  * direct charging results in //tapering// charge current, decreasing as battery bank voltage / SoC increases.((among other factors)).  So over an hour the current might go from 30A to 10A, an average of 20A. 20A x 1 hour = **20Ah replaced**.  Pro:  your bank gets more charging when it needs it most.  Con:  charge rates are less predictable until you learn how your system works.
+  * [[electrical:12v:b2b|DC-DC charging]] generally make its rated output (20A, for example) for the majority of the charging cycle.  Pro:  highly predictable charging (20A x 1 hour = **20Ah replaced**).  Con:  charging current is the ~same regardless of bank SoC
+  * in this artificial example both charging setups will replace 20Ah in an hour of charging but they do it differently.  In reality which charges "better" depends on your specific use case, bank chemistry & capacity, alternator voltage and rating, DC-DC rating, etc.  Do your research and pick your poison.
 ==== flooded lead-acid ====
@@ Line 551: / Line 560: @@
   * LiFePO4 resting voltages are high enough they may hold the circuit closed on VSRs designed for lead chemistries.  Workaround:  [[electrical:12v:alternator#disabling_alternator_charging|disable alternator charging]] (at least momentarily) after driving or install DC-DC.  Or just let it work that way.
   * Voltage-sensing relays can be unintentionally triggered((dVSR)) or "held closed"((both VSR and dVSR)) [[http://bdp.mousetrap.net/index.php/2018/10/27/side-effect-of-solar-alternator-charging/|by voltage from the solar-charged side]] in some scenarios.   Workaround:  address with HVD as below if desired, or with a [[electrical:12v:b2b|DC-DC charger]], or by adding a switch to disable the VSR.((a momentary-off switch would kill the connection, although an ON/OFF switch might be useful for other purposes))
-  * In early morning or other times when house battery voltage is lowest, **a plain solenoid may unintentionally allow depleted batteries to pull down the starter battery**.  Workarounds:  use a VSR, a DC delay timer, a DC-DC charger, or start the vehicle immediately after inserting the key((ie, do not leave in the Accessory position which would drain the starter battery)).
+  * On ignition-triggered((IGN, D+)) setups if the key is turned to ACC but the engine not started a depleted house battery can pull down the starter battery**.  Workarounds:  use a VSR, a DC delay timer, a DC-DC charger, or start the vehicle immediately after inserting the key((ie, do not leave in the Accessory position which would drain the starter battery)).
   * Solar charging while the engine is running may [[opinion:frater_secessus:alternatorSolarStall|get "stuck" at alternator voltage]].  Workaround:  higher solar wattage, DC-DC charger, or diode/FET-based isolator, or a switch to disconnect isolator after alternator voltage is reached.  The [[https://amzn.to/3h5iMUd|Victron Cyrix-ct isolator]] could be useful here, as it appears to disconnect >13.8v.((https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-ct-120A-230A-EN.pdf))
   * Alternator charging may bring some battery chemistries (like bare lithium cells with no BMS) to **unsuitably high voltages**.  Workarounds:  A [[electrical:12v:hvd|high voltage disconnect]] can [[electrical:12v:alternator charging hvd|restrict alternator charging to lower voltages]].  [[electrical:12v:b2b|DC-DC chargers]] can also regulate voltage provided to the house battery.

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