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electrical:depth_of_discharge [2023/05/29 12:00] frater_secessus [SoC by voltage] |
electrical:depth_of_discharge [2023/08/17 20:43] frater_secessus [effect of DoD on battery life] |
===== Depth of discharge / State of Charge ===== | ===== Depth of discharge / State of Charge ===== |
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{{ 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. |
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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. |
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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%. |
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Note: This information is primarily relevant to lead-chemistry batteries. Lithium batteries have different DoD capabilities and lifecycles. | |
===== effect of DoD on battery life ===== | |
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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)) | |
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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.)) | |
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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. | |
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| | **T105 Ah**| | **Cost**| **weight per set**| **Target Ah**| | | | | |
| | 225| | $260.00| 124| 175| | | | | |
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| **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%. | |
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| 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]]. |
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===== estimatating SoC ===== | ===== estimatating SoC ===== |
This section [[electrical:12v:psoc|has moved]]. | This section [[electrical:12v:psoc|has moved]]. |
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| ===== lithium SoC ===== |
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| 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. |