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electrical:solar:shallow_cycling [2017/11/09 19:06] frater_secessus [how it works] |
electrical:solar:shallow_cycling [2020/11/30 17:57] frater_secessus [components] |
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, simple, space-efficient, and inexpensive solar configuration that may be of use to cardwellers or minimalist vandwellers. |
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Most of the RV world is familiar with deep-cycle 12v systems; these are intended to store power for use overnight. If most power is only needed in the daytime then deep-cycle batteries are not required. | 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)) | 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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===== non-cycling ===== | ===== non-cycling ===== |
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//Non-cycling// is the use of solar power only when the battery is fully charged. | //Non-cycling// is the use of solar power only when the battery is fully charged. The starter battery is even more fully charged than in normal vehicles. |
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==== how it works ==== | ==== how it works ==== |
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- a simple [[electrical:solar:charge_controller#shunt_controller|shunt charge controller]] holds the battery at a mild Absorption voltage (14.0, - 14.2v) when charging, just below the 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; this ensures the starter battery is never discharged below 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 === |
If **running larger loads** (fans, laptop chargers) the setpoint should be set higher (like 13.5v - 14.0v). This is because the panel will be able to make more power closer to Vmp. Consider the popular [[http://amzn.to/2you3Kj|Renogy 100w panel]] that puts out about 5.29A. At the lower LVR the panel((under lab conditions)) will make **68.77W**. At the higher LVRs the panel will make **71.42-74.06W** | If **running larger loads** (fans, laptop chargers) the setpoint should be set higher (like 13.5v - 14.0v). This is because the panel will be able to make more power closer to Vmp. Consider the popular [[http://amzn.to/2you3Kj|Renogy 100w panel]] that puts out about 5.29A. At the lower LVR the panel((under lab conditions)) will make **68.77W**. At the higher LVRs the panel will make **71.42-74.06W** |
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Note: running a small MPPT [[electrical:solar:charge_controller|charge controller]] would make this immaterial, as the controller would run the panel at max power (Vmp) at 18.9v. | Note: running a small [[electrical:solar:charge_controller#mppt|MPPT]] [[electrical:solar:charge_controller|charge controller]] would make this immaterial, as the controller would run the panel at max power (Vmp) at 18.9v. |
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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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===== shallow-cycling ===== | ===== shallow-cycling ===== |
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//Shallow-cycling// is a more aggressive approach, allowing for a bit of power after sundown. It is most **suitable for starter batteries with removable cell caps**. | //Shallow-cycling// is a more aggressive approach, allowing for more power in the daytime and some power for use after sundown. It is most **suitable for starter batteries with removable cell caps**. |
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The charging setpoint is set somewhat higher, ~14.4v. This will result in minor outgassing and a bit more power (**76.18W** using the panel data above). [[electrical:12v:charging#watering_batteries|Battery watering]] is mandatory. | The charging setpoint is set somewhat higher, ~14.4v. This will result in minor outgassing and a bit more power (**76.18W** using the panel data above). [[electrical:12v:charging#watering_batteries|Battery watering]] is mandatory. |
Starter batteries are designed for about 15% depth of discharge((http://forum.solar-electric.com/discussion/comment/60412#Comment_60412)). We can set the Low Voltage Disconnect (//Vlvd//) to 12.5-12.6v as a floor. In a typical starter battery this could be 5Ah of power usable at night, enough to run an LED light for hours as well as run a small fan all night. All device charging should happen in daylight when power is relatively plentiful. | Starter batteries are designed for about 15% depth of discharge((http://forum.solar-electric.com/discussion/comment/60412#Comment_60412)). We can set the Low Voltage Disconnect (//Vlvd//) to 12.5-12.6v as a floor. In a typical starter battery this could be 5Ah of power usable at night, enough to run an LED light for hours as well as run a small fan all night. All device charging should happen in daylight when power is relatively plentiful. |
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If the starter battery (when it eventually dies a natural death) were replaced with [[electrical:12v:deep_cycle_battery#chain_store_batteries|a 12v wally world marine battery]] one might be able to cycle to 25% DoD. This would mean an Vlvd of ~12.4v and 8-9Ah of power at night. | If the starter battery (when it eventually dies a natural death) were replaced with [[electrical:12v:deep_cycle_battery#chain_store_batteries|the heaviest 12v wally world marine battery]] that would fit one might be able to cycle to 25% DoD. This would mean an Vlvd of ~12.4v and 8-9Ah of power at night. |
===== effect on starter battery ===== | ===== effect on starter battery ===== |
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> "most of the "defective" batteries returned to manufacturers during free replacement warranty periods are good"((https://www.batterystuff.com/kb/articles/battery-articles/how-do-batteries-die.html)) | > "most of the "defective" batteries returned to manufacturers during free replacement warranty periods are good"((https://www.batterystuff.com/kb/articles/battery-articles/how-do-batteries-die.html)) |
... A charging regime might even extend the perceived longevity of the starter battery. | ... A charging regime might even extend the perceived longevity of the starter battery. |
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| Anecdote: TreborEnglish runs his 75A flooded 12v wally world deep cycle to 87% SoC regularly and it has lasted 3 years as of this writing. He reports it requires 20-30ml of water/month.((https://www.reddit.com/r/vandwellers/comments/enwq70/best_car_battery_for_van_life/fe670is/)) |
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| ===== sample build ===== |
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| Total cost, ~$140. |
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| * 100w poly((for least expensive and best performance with [[electrical:solar:shunt_tweaking|shunt]]/[[electrical:solar:pwm_tweaking|pwm [[electrical:solar:charge_controller|controllers]]]])) panel on the roof, either a [[https://amzn.to/2snWQOL|rack-mounted framed panel]] that fits rack dimensions or a [[https://amzn.to/30rmAGD|flex panel]] adhered to the surface. |
| * [[https://amzn.to/2ToGWyX|cable gland]] for getting wires through roof |
| * panel wires runs down the vehicle A-pillar inside the passenger area((can be on driver or passenger side depending on where starter battery is located)) and into the PANEL terminals of a [[electrical:solar:shunt_tweaking|$10 shunt]] solar [[electrical:solar:charge_controller|charge controller]] mounted in the footwell or elsewhere |
| * [[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 |
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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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