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--- electrical:12v:battery_capacity [2017/05/26 23:49]
frater_secessus
+++ electrical:12v:battery_capacity [2025/06/24 19:12] (current)
frater_secessus [C notation]
@@ Line 1: / Line 1: @@
 ====== C notation ======
-Battery capacity in Amp-hours is written as **C**.  This notation is most useful when talking about charging/discharging rates.
+**C** notation is used to express the relationship of a bank's capacity to charge/discharge current.   Example:  a 20A current into or out of a 100Ah bank is //0.2C// (20A / 100Ah).  The same calculation could be made with W/Wh since it's about the relationship between the two and not any specific unit of measurement.
-Examples:
+This relationship can also be described as a fraction;  the above would be //C/5//.
-If you have a 200AH battery bank then C = 200AH.
-If the manufacturer recommends max //charging// at C/5 the rate should be at or below 40A (200/5). \\
-If the manufacturer recommends max charging at C((sometimes written as 1C)) the rate should be at or below 200A (1x200). \\
-Note: the **usual charge rate** for deep cycle batteries is C/10.  Sometimes manufacturers express that [[electrical:12v:charging|Absorption stage]] is complete((and therefore Float should commence)) when the bank is holding Vabs and charging current has dropped to C/100 or C/200.
-If the manufacturer recommends max //discharge// (load) be 3C the rate should be at or below 600A (3x200). \\
+Note:  most deep cycle manufacturer's rate capacity at C/20 (0.05C), due to Peukert effect on lead chemistries (see below).((Lithium doesn't not have a significant Peukert effect.  Capacity measured by C/20 and by amp-counting will be nearly identical)).  In other words, a 100Ah battery will deliver 100A with a 5A load over 20 hours.
-Note:  most deep cycle manufacturer's rate capacity at C/20, due to Peukert effect.
+===== Examples =====
+Assuming a 200Ah bank:
+  * If the manufacturer recommends max //charging// at 0.2C the rate should be ≤40A (200 x 0.2)
+  * If the manufacturer recommends minimum charging at C110 the rate should be ≤20A (200 x 0.1)
+  * If the manufacturer recommends max //discharge// (load) be 3C the rate should be ≤600A (200 x 3)
+  * If the manufacturer says that [[electrical:12v:charging|Absorption stage]] is complete when charging current current has dropped to ≤0.05C then the current to watch for would be ≤10A (200 x 0.05)
+===== other than 20hr rates =====
+Because of the Peukert effect, lead bank //measured// capacities are strongly affected by dicharge rate. Sample data below is for flooded lead acid.((Due to lower internal resistance AGM is less affected by discharge rate and lithium is barely affected at all.))  C/20 capacity is multiplied by the factor below to find projected capacity at given discharge rates.
+Example:  our battery is rated at 100Ah when drained at 5A over 20 hours.  If it is drained at 20A in 5 hours it will have an observed capacity of 70Ah (100Ah x .7).
+Hour = .3 \\
+Hour = .5 \\
+hour = .6 \\
+hour = .65 \\
+hour = .7 \\
+hour = .75 \\
+hour = .8 \\
+hour = .85 \\
+hour = .9 \\
+hour = .95 \\
+hour = 1 \\
+hour = 1.05 \\
+hour = 1.1 \\
+hour = 1.25 \\
+hour = 1.30((vhttps://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/11731-peukert-law-batteries-and-you#post11731))

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