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--- electrical:12v:mandatory_dcdc [2023/05/09 14:32]
frater_secessus [situations where DC-DC is effectively required]
+++ electrical:12v:mandatory_dcdc [2024/07/15 13:15] (current)
frater_secessus [Is DC-DC charging mandatory?]
@@ Line 3: / Line 3: @@
 ====== Is DC-DC charging mandatory? ======
-Death and taxes are mandatory.  Gravity is mandatory.
+Death and taxes are mandatory.  Gravity is mandatory. Are DC-DC chargers mandatory? Ehh...
+In many/most situations, direct-charging the house bank with [[electrical:12v:alternator#combiners|a combiner]] (relay, isolator, VSR)  is both effective and inexpensive. Even [[electrical:12v:directcharginglfp|with lithium banks]].
-In many/most situations direct-charging the house bank with [[electrical:12v:alternator|a combiner]] (relay, isolator, VSR)  is both effective and inexpensive. Even [[electrical:12v:directcharginglfp|with lithium banks]].
+However, **some use cases may require a DC-to-DC charger**. These are much more intelligent (and expensive) devices that sit in between the vehicle batteries and the house batteries, and actively adjust both the voltage and current flowing from the vehicle's electrical system and into the house batteries.
-There //are// scenarios where one may want to [[electrical:12v:alternator#disabling_alternator_charging|disable the combiner]].
+**Note:** This article is just the TL;DR of DC-DC charger options. [[electrical:12v:b2b|More detailed info is here]].
-===== situations where DC-DC is effectively required =====
+===== Situations where DC-DC is effectively required =====
-  * when the vehicle has a smart (variable-voltage) alternator, more common in Europe
+  * When the vehicle has a smart (variable-voltage) alternator
-  * small alternators vs. ginormous battery banks of any chemistry
+    * Common on European vehicles, and on American vehicles newer than ~2017
-  * exotic alternator or battery bank voltages, including setups like 24v house bank and 12v alternator (or //vice versa//)
+  * Small alternators vs. ginormous battery banks of //any// chemistry
-  * if one needs relatively-stable charge rates.  All other things being equal, direct-charging current is dictated by the difference in voltage ("delta") between alternator and battery bank (I=**V**/R).   Therefore...
+  * Exotic alternator or battery bank voltages, including setups like 24v house bank and 12v alternator (or //vice versa//)
-      * ...anything that increases the difference (higher alt voltage, lower bank voltage, loads on the bank) will increase current drawn from the alternator
+  * If one needs relatively-stable charge rates((direct-charging rates "taper" as bank voltage rises))
-      * ... and anything that decreases the difference (like rising bank State of Charge) will decrease the current.  So direct-charged banks tend to start out with higher current and "taper" off to lower and lower currrent as they charge
+  * If you want to impose an arbitrary current limit((0.2C for Gel, 0.4C for lithium, etc))
-      * DC-DC chargers boost alternator voltage, maintaining  sufficient voltage delta for more consistent current output as long as the bank can accept it.
+  * when the alternator is the only charging source for the lead-chemistry house batteries. In this case DC-DC won't help with [[electrical:12v:charging#absorption_stage|Absorption]] duration((the vehicle is usually not running long enough to fully charge lead-chemistry batteries)) but it can help with Absorption //voltage//.
-  * if you want to impose an arbitrary current limit((0.2C for Gel, 0.4C for lithium, etc))
   * <del>when an influencer says so</del>
   * <del>when Chicken Little claims you need one or the sky will fall</del>
-===== situations where DC-DC is preferable =====
+===== Situations where DC-DC is preferable =====
-  * lead house bank when alternator is [[electrical:12v:alt_and_solar#how_solar_helps|the only charging source]]
-In this case DC-DC won't help with [[electrical:12v:charging#absorption_stage|Absorption]] duration((the vehicle is usually not running long enough to fully charge lead-chemistry batteries fully)) but it can help with Absorption //voltage//.
+  * when the alternator is the sole charging source for LiFePO4.  In this situation DC-DC will deliver more predictable and often faster charging, particularly when the bank is at higher SoC.

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