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--- electrical:12v:battery_capacity [2021/05/03 14:40]
frater_secessus [other than 20hr rates]
+++ 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**.  100Ah, for example.
+**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.
-C notation can also be used to describe the **relative amount of current** charging/discharging battery bank. For example a 50A load on a 100Ah bank would be C/2 (100/2 == 50).((technically C/20/2, but that form is rarely seen outside formal documents)). It may also be written as 0.5C.((decimal vs. fractional expression, can be used interchangably))
+This relationship can also be described as a fraction;  the above would be //C/5//.
-Note:  most deep cycle manufacturer's rate capacity at C/20, 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 (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.
 ===== Examples =====
-If you have a 200AH battery bank then C = 200AH.
+Assuming a 200Ah bank:
-If the manufacturer recommends max //charging// at C/5 the rate should be at or below 40A (200/5). \\
-If the manufacturer recommends minimum charging at C/10 the rate should be at or above 20A (200/10). \\
-If the manufacturer recommends max //discharge// (load) be 3C the rate should be at or below 600A (3x200). \\
-If the manufacturer says that [[electrical:12v:charging|Absorption stage]] is complete when charging current has dropped to C/100 or C/200 then the current to watch for would be 2A (200/100) or 1A (200/200).
+  * 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 =====

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