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electrical:depth_of_discharge [2020/11/26 10:17] frater_secessus [SoC by voltage] |
electrical:depth_of_discharge [2023/08/17 20:44] frater_secessus [partial state of charge] |
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===== Depth of discharge / State of Charge ===== | ===== Depth of discharge / State of Charge ===== | ||
- | {{ http:// | + | {{ http:// |
- | For solar powered systems the greatest | + | DoD is the inverse of //State of Charge |
- | DoD has a **significant impact on longevity of deep cycle batteries**. | + | DoD has a **significant impact on longevity of lead deep cycle batteries**.((and, to a lesser degree, lithium batteries)) |
- | ===== 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 | + | |
- | + | ||
- | + | ||
- | The **most common discharge limit for deep cycle batteries is 50% DoD**. | + | |
- | + | ||
- | 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**| | + | |
- | | | 225| | $260.00| | + | |
- | | | | | | | | | | | | + | |
- | | | | | | | | | | | | + | |
- | | | | | | | | | | | | + | |
- | | **DoD**| | + | |
- | | 10| 90| 22.5| | | | | | | | + | |
- | | 20| 80| 45| 3000| 135| $1.93| | + | |
- | | 30| 70| 67.5| 2250| 151.875| | + | |
- | | 40| 60| 90| 1450| 130.5| | + | |
- | | 50| 50| 112.5| | + | |
- | | 60| 40| 135| 1050| 141.75| | + | |
- | | 70| 30| 157.5| | + | |
- | | 80| 20| 180| 800| 144| $1.81| | + | |
- | One can choose to [[electrical: | + | |
+ | Note: This information (including the chart to the right) is primarily relevant to lead-chemistry batteries. | ||
===== estimatating SoC ===== | ===== estimatating SoC ===== | ||
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* intermittent heavier loads that leave the system with measured >=12.2v when that load is removed | * intermittent heavier loads that leave the system with measured >=12.2v when that load is removed | ||
- | The more challenging task is judging when to kill the circuit based on voltage **under heavier loads**. | + | The more challenging task is judging when to kill the circuit based on voltage **under heavier loads**. |
+ | |||
+ | {{ https:// | ||
+ | |||
+ | For a 200A bank 50% DoD would be 12.1v at rest, ~12.0v at C/10 (20A discharge), ~11.55v at C/5 (40A discharge), and 11.2v at C/3 (~70A discharge). | ||
+ | |||
+ | It may take experimentation with your system to see where the battery voltage rebounds after removing the heavy loads. | ||
- apply expected load | - apply expected load | ||
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If the battery rebounds to the desired voltage then repeat to deeper discharge. | If the battery rebounds to the desired voltage then repeat to deeper discharge. | ||
+ | An [[electrical: | ||
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This section [[electrical: | This section [[electrical: | ||
+ | ===== effect of DoD on lead 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**. | ||
+ | |||
+ | 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**| | ||
+ | | | 225| | $260.00| | ||
+ | | | | | | | | | | | | ||
+ | | | | | | | | | | | | ||
+ | | | | | | | | | | | | ||
+ | | **DoD**| | ||
+ | | 10| 90| 22.5| | | | | | | | ||
+ | | 20| 80| 45| 3000| 135| $1.93| | ||
+ | | 30| 70| 67.5| 2250| 151.875| | ||
+ | | 40| 60| 90| 1450| 130.5| | ||
+ | | 50| 50| 112.5| | ||
+ | | 60| 40| 135| 1050| 141.75| | ||
+ | | 70| 30| 157.5| | ||
+ | | 80| 20| 180| 800| 144| $1.81| | ||
+ | One can choose to [[electrical: | ||
+ | |||
+ | |||
+ | ===== lithium SoC ===== | ||
+ | |||
+ | Lithium chemistries have very flat voltage curves, making it notoriously difficult to gauge SoC by voltage. |