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====== C notation ======

**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.  

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 (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 =====

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).


1 Hour = .3 \\
2 Hour = .5 \\
3 hour = .6 \\
4 hour = .65 \\
5 hour = .7 \\
6 hour = .75 \\
8 hour = .8 \\
10 hour = .85 \\
12 hour = .9 \\
16 hour = .95 \\
20 hour = 1 \\
24 hour = 1.05 \\
36 hour = 1.1 \\
72 hour = 1.25 \\
100 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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