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electrical:solar:shallow_cycling [2020/01/14 15:58] frater_secessus [sample build] |
electrical:solar:shallow_cycling [2020/11/30 18:05] frater_secessus [microsolar without deep-cycle batteries] |
====== microsolar without deep-cycle batteries ====== | ====== microsolar without deep-cycle batteries ====== |
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This article describes a small, simple, space-efficient, and inexpensive solar configuration that may be of use to cardwellers or minimalist vandwellers. | This article describes a small, cheap, simple, space-efficient solar configuration that may be of use to cardwellers or minimalist vandwellers. Benefits: |
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| * provides 12v power during daylight |
| * will never deplete the starter battery so you get stranded |
| * actively maintains the starter battery |
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| Instead of deep-cycling like someone might in an RV, the idea here is the starter battery can be used but never dragged below 100% state of charge)). |
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| ==== components ==== |
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| * vehicle with starter battery (you already have this!) |
| * simple [[http://amzn.to/2z8Sd8Y|10A controller **with configurable setpoints**]]. The controller should be mounted in a location easy for easy access if the built-in USB ports are going to be used. |
| * small solar panel; 100W is common. |
| * connector of some kind if panel is mounted off-vehicle; cable gland if the panels are mounted on the vehicle and the wire is passed through the |
| * wiring from panel to controller and from controller to starter battery |
| * [[http://amzn.to/2xHjBi7|usb/12v power outlet]]. An outlet with USB ports in it would allow the controller itself to be mounted discreetly and closer to the battery. |
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Most of the RV world is familiar with [[electrical:12v:deep_cycle_battery|deep-cycle 12v systems]]; these are intended to store power for use overnight. If most power is consumed [[electrical:solar:nonessential|in the daytime when the system has excess power]] then deep-cycle batteries may not be required. | |
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Instead of deep-cycling, the starter battery is //non-cycled//((never discharged below 100% state of charge)) as described below. It can also be [[electrical:solar:shallow_cycling#shallow-cycling|shallow-cycled]].((discharged to 90% state of charge)) | |
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==== how it works ==== | ==== how it works ==== |
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- a simple [[electrical:solar:charge_controller#shunt|shunt charge controller]] holds the battery at a mild Absorption voltage (14.0, - 14.2v) when charging, just below the significant gassing point | - a simple [[electrical:solar:charge_controller#shunt|shunt charge controller]] holds the starter battery at a medium Float voltage (13.2 - 13.8v, see notes [[electrical:solar:shallow_cycling#charging_voltages_and_starter_batteries|below]]) when charging, this is below the gassing point |
- the controller's LOAD output disconnects (LVD) at 100% SoC (~12.7v) | - the controller's LOAD output disconnects (LVD) at 100% SoC (~12.7v) |
- the controller's LOAD output //re//connects (LVR) at ~13.0v); see discussion below | - the controller's LOAD output //re//connects (LVR) at ~13.0v) |
- power is //only// taken from the controller's LOAD output;((or from a circuit control by a relay on the LOAD output)) this ensures the starter battery is never discharged below [[electrical:12v:lvd|the intended setpoint]] | - power is //only// taken from the controller's LOAD output;((or from a circuit control by a relay on the LOAD output)) this ensures the starter battery is never discharged below [[electrical:12v:lvd|the intended setpoint]]. Since the load is disconnected below 12.7v the battery cannot be run down by loads. |
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=== Low Voltage Reconnect (LVR) setpoint === | === Low Voltage Reconnect (LVR) setpoint === |
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==== components ==== | |
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* vehicle with starter battery | |
* simple [[http://amzn.to/2z8Sd8Y|10A controller **with configurable setpoints**]]. The controller should be mounted in a location easy for easy access if the built-in USB ports are going to be used. | |
* small solar panel; 25w-100W would be fine. | |
* connector of some kind if panel is mounted off-vehicle | |
* wiring from panel to controller and from controller to starter battery | |
* [[http://amzn.to/2xHjBi7|usb/12v power outlet]]. An outlet with USB ports in it would allow the controller itself to be mounted discreetly and closer to the battery. | |
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* [[https://amzn.to/2RhbHmD|wire]] run from controller's BATTERY terminals to the starter battery. | * [[https://amzn.to/2RhbHmD|wire]] run from controller's BATTERY terminals to the starter battery. |
* wire run from controller's LOAD terminals to [[https://amzn.to/3adk9vJ|12v/usb outlet]], power bus, etc | * wire run from controller's LOAD terminals to [[https://amzn.to/3adk9vJ|12v/usb outlet]], power bus, etc |
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| ===== charging voltages and starter batteries ===== |
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| The chemistry of starter and "hybrid" ("marine") batteries is somewhat different than deep cycle batteries. Speciically, starter batteries typically have calcium added to the positive grid to minimize self-discharge and outgassing. |
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| Problem: calcium-enhanced grids are more susceptible to "positive grid corrosion" from sustained higher voltages. |
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| The question is this: **what voltage can starter batteries be held at without damage**? One answer might be be "alternator voltage" since that's already happening when we drive vehicles, and they are not damaged by long journeys. |
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| ==== staged charging ==== |
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| CTEK's starter battery charger designed to be left on charges thusly:((https://www.ctek.com/storage/9E4D59B2526B4C3C54C61873C881CAACFC4C93F306DE1C8A2788E26EA6E506DA/f9b26d5eaeeb4787a51e5fc933ae1eae/pdf/media/687dd00827b44e44afee8695c5d0efab/MXS_3.8-manual-low-UK-EN.pdf)) |
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| * 14.4v Absorption |
| * 13.6v Float |
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| So a charge controller with that configuration should be gentle enough on the battery. |
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| ==== single voltage charging ==== |
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| This is the tricky part. Shunts (or controllers set with [[electrical:12v:eternal_absorption|Vabs == Vfloat]]) have one charging voltage. What should we use? |
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| * folks who shallow cycle might charge to 14.4v to help counteract sulfation from overnight cycling. |
| * folks who non-cycle might charge to 13.6v as if the battery is simply being maintained. This leaves some power on the table (~8.5%) for non-MPPT controllers but may be easier on the battery. |
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