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--- opinion:frater_secessus:charging_faster [2020/04/18 13:28]
frater_secessus [charging faster isn't always better]
+++ opinion:frater_secessus:charging_faster [2023/07/15 11:05] (current)
frater_secessus [lithium]
@@ Line 2: / Line 2: @@
-There is a common misperception that charging one's battery banks //faster// is //better// or worth throwing more money at.  Here are some reasons it is not always true:
+There is a common misperception that charging one's battery banks //faster// is //better// or that having more charging capacity guarantees faster charging.  Here are some reasons it is not always true:
-**Lead batteries** have a **maximum amount of current** they will accept, typically [[electrical:12v:battery_capacity|C/3]] for AGM and C/5 for flooded. So if you have 100Ah of AGM the most it will want to take is something like ~33A.  Installing 50A-100A of charging capacity can't force-feed the battery any faster.((it may help run loads, though))
-** Deep-cycled lead batteries have a lengthy [[electrical:12v:charging|Absorption]] stage** that cannot be sped up. Depending on use, Absorption typically requires several hours.There is a saying that "it takes 9 months to make a baby, but two women cannot make a baby in 4.5 months".  Same with absorption - it takes what it takes and you cannot hurry it.
+===== lead-acid =====
-**Lithium batteries** can slurp up current wildly, but shouldn't for their own health.  Lithium lasts longest in sub-C use (ie, less than 100A for a 100Ah Li bank).  C/2 (50A) is a more common limit to keep from stressing them. In commercial examples the BMS will limit current to protect the cells.  A small [[electrical:12v:b2b|DC-DC charger]] can help protect bare cells from their own greediness.
+**Lead batteries** have a **maximum amount of current** they will accept, typically [[electrical:12v:battery_capacity|C/3]] for AGM and C/5 for flooded. So if you have 100Ah of AGM the most it will want to take is something like ~33A.  Once the battery's limit is hit throwing more charging capacity at it can't charge it any faster.((it may help run loads, though))
+** Deep-cycled lead batteries have a lengthy [[electrical:12v:charging|Absorption]] stage** that cannot be sped up((at least not more than a few percent, see below)). Depending on use, Absorption typically requires several hours.There is a saying that "it takes 9 months to make a baby, but two women cannot make a baby in 4.5 months".  Same with absorption - it takes what it takes and you cannot hurry it in the normal sense.
+However:
+> charge current affects the SOC transition point from bulk to absorption charging - MaineSail((https://marinehowto.com/how-fast-can-an-agm-battery-be-charged/))
+MaineSail found that
+  * charging AGM at C/2.5 (max rate) resulted in the battery being 63.3% "full"((amp-wise)) at Vabs and being fully charged in **5hrs, 30 minutes** (20min Bulk, 5hr 10mins Absorption)
+  * charging AGM at C/5 (min rate) resulted in the battery being 77.4% "full" at Vabs and being fully charged in **5hrs, 42 minutes** (76min Bulk, 4hr 26mins Absorption)
+Note that the **using 2x the charging current only sped up the whole process by 12 minutes (3.6%)** due to Vabs starting earlier but taking longer.
+  * **Getting to Vabs faster** could be [[electrical:solar:pwm_tweaking|preferable on PWM controllers]], as the system would be making max power for a longer period of time.
+  * **Getting to Vabs slower** could be preferable on timer-based Absorption configurations((like 180 minutes)), as slower charging regiment would reduce the required Absorption duration.((180/266mins rather than 180/310mins))
+===== lithium =====
+**Lithium batteries** can slurp up current wildly, but shouldn't for their own health.  Lithium lasts longest in sub-C use (ie, less than 100A for a 100Ah Li bank).  0.5C (50A) is a more common manufacturer recommendation, and folks [[electrical:12v:drop-in_lifepo4#an_approach_to_greater_longevity|striving for added longevity]] might limit it to 0.2C (20A). There is some evidence that 0.4C rates are acceptable for long life when combined with gentle charging voltages like 3.45Vpc.((FIXME  - insert Rod's testing of 2011 bank here))
+In commercial examples the BMS will limit current (typically to 1C) to protect the cells.  A small [[electrical:12v:b2b|DC-DC charger]] can help protect bare cells from their own greediness.
+Limiting charging  current also makes it easier on alternators when they are used to charge Li.

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