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electrical:depth_of_discharge [2021/02/21 13:33]
frater_secessus [SoC by voltage] 		electrical:depth_of_discharge [2023/08/17 20:43]
frater_secessus [effect of DoD on battery life]
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 ===== Depth of discharge / State of Charge ===== ===== Depth of discharge / State of Charge =====
  
-{{ http://popupbackpacker.com/wp-content/uploads/2013/12/State-of-Charge-Chart-Trojan.jpg?200|}}//Depth-of-discharge (DoD or DOD)// refers to how low a deep cycle battery is taken between [[electrical:12v:charging|full charges]].  DoD is the inverse of //State of Charge (SoC)//.  Example:  a battery at 30% DoD is at 70% SoC.+{{ http://popupbackpacker.com/wp-content/uploads/2013/12/State-of-Charge-Chart-Trojan.jpg?200|}}//Depth-of-discharge (DoD or DOD)// refers to how low a deep cycle battery is taken between [[electrical:12v:charging|full charges]].  Specifically, what percentage of the rated capacity remains at a given point?   Example:  For solar powered systems the greatest DoD (and therefore lowest SoC) will be in early morning just before the panels start creating power again.
  
-For solar powered systems the greatest DoD (and therefore lowest SoC) will be in early morning just before the panels start creating power again.+DoD is the inverse of //State of Charge (SoC)//.  Example:  a battery at 30% DoD is at 70% SoC.
  
-DoD has a **significant impact on longevity of deep cycle batteries**.  For this reason [[electrical:inverter|Inverters]] and other high-load devices may have a [[electrical:12v:lvd|low voltage cutoff]]. +DoD has a **significant impact on longevity of lead deep cycle batteries**.((and, to a lesser degree, lithium batteries))  For this reason [[electrical:inverter|Inverters]] and other high-load devices may have a [[electrical:12v:lvd|low voltage cutoff]] to prevent going below a given SoC, typically 50%.  
-===== effect of SoC on battery life ===== +
- +
-How deeply one regularly discharges lead-chemistry batteries will have a **direct effect on how long the battery bank will last**.((Banks are typically replaced when they have lost 20% of their capacity)) +
- +
- +
-The **most common discharge limit for deep cycle batteries is 50% DoD**.  This gives a good balance between usability and longevity.  The **lowest cost per Ah** occurs around 30% DoD although this requires buying, installing, and moving //dead lead// or unusable battery capacity.((20% DoD is the limit at which manufacturers rate their battery's cycles.))   +
- +
-Based on the following data on the Trojan T-105: +
-  * lowest cost per Ah happens at 30% DoD +
-  * longest life happens at 20% DoD +
-  * least battery weight happens at 80% DoD +
-so make your DoD decision based on what is most important to you. +
- +
-| |  **T105 Ah**| |  **Cost**|  **weight per set**|  **Target Ah**| | | | +
-| |  225| |  $260.00|  124|  175| | | | +
-| | | | | | | | | | +
-| | | | | | | | | | +
-| | | | | | | | | | +
-|  **DoD**|  **State of Charge**|  **power per cycle**|  **Num. of cycles**|  **lifetime power in kAh((Ah *  1000))**|  **levelled cost / Kah**|  **life in years**|  **Sets needed for target Ah**|  **Weight**| +
-|  10|  90|  22.5| | | | | | | +
-|  20|  80|  45|  3000|  135|  $1.93|  8.2|  3.9|  482| +
-|  30|  70|  67.5|  2250|  151.875|  $1.71|  6.2|  2.6|  321| +
-|  40|  60|  90|  1450|  130.5|  $1.99|  4.0|  1.9|  241| +
-|  50|  50|  112.5|  1200|  135|  $1.93|  3.3|  1.6|  193| +
-|  60|  40|  135|  1050|  141.75|  $1.83|  2.9|  1.3|  161| +
-|  70|  30|  157.5|  900|  141.75|  $1.83|  2.5|  1.1|  138| +
-|  80|  20|  180|  800|  144|  $1.81|  2.2|  1.0|  121| +
-One can choose to [[electrical:severe battery use|run the batteries quite hard]] in emergency or temporary conditions with the understanding that it will likely "hurt" the batteries to some degree.  Consistently going past 50% DoD will greatly reduce the battery's usable cycles.  Some studies suggest discharging to 80% yields 1/10th the number of cycles available at 20%.  +
  
 +Note: This information (including the chart to the right) is primarily relevant to lead-chemistry batteries.  Lithium batteries have [[#lithium_soc|different DoD capabilities and lifecycles]].
  
 ===== estimatating SoC ===== ===== estimatating SoC =====
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 If the battery rebounds to the desired voltage then repeat to deeper discharge.  Stop when the battery no longer can rebound to the setpoint.  The LVD voltage is the lowest voltage the system can  drop to and still rebound to the desired setpoint when the load is removed.  If the battery rebounds to the desired voltage then repeat to deeper discharge.  Stop when the battery no longer can rebound to the setpoint.  The LVD voltage is the lowest voltage the system can  drop to and still rebound to the desired setpoint when the load is removed. 
  
 +An [[electrical:12v:battery_monitor|amp-counting battery monitor]] may be useful here. 
  
  
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 This section [[electrical:12v:psoc|has moved]]. This section [[electrical:12v:psoc|has moved]].
  
 +===== lithium SoC =====
 +
 +Lithium chemistries have very flat voltage curves, making it  notoriously difficult to gauge SoC by voltage.  In this case [[electrical:12v:battery_monitor|a shunted battery monitor]] is used to count amps as they go in/out.  If the Li battery has connectivity you may be able to read SoC from the internal BMS. 
electrical/depth_of_discharge.txt · Last modified: 2023/08/17 21:36 by frater_secessus

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