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electrical:12v:alt_and_solar [2018/06/02 10:20]
frater_secessus [how solar helps] |
electrical:12v:alt_and_solar [2020/05/24 12:00]
frater_secessus [gotchas] |
| ====== Augmented solar charging ====== | ====== Augmented solar charging ====== |
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| Note: although this page was written with alternator-augmented solar charging in mind, the general principles also apply to [[electrical:shore_power|shore power charging]] and [[electrical:generator|generator]] charging. | Note: although this page was written with alternator-augmented [[electrical:solar|solar]] charging in mind, the general principles also apply to [[electrical:shore_power|shore power charging]] and [[electrical:generator|generator]] charging. |
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| Alternator + solar charging has considerable benefits over [[electrical:12v:alternator|alternator charging alone]], and over solar alone. | Alternator + solar charging has considerable benefits over [[electrical:12v:alternator|alternator charging alone]], and over solar alone. |
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| ===== how solar helps ===== | ===== how solar helps ===== |
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| | Solar works anytime there is available sunlight, not just when the vehicle is running. |
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| Alt charging alone is unlikely to get lead-acid chemistries fully charged since Absorption can take hours. Incomplete charge ([[electrical:12v:psoc|Partial State of Charge]], or PSOC) over time will result in [[electrical:batterycide|battery murder]]. | Alt charging alone is unlikely to get lead-acid chemistries fully charged since Absorption can take hours. Incomplete charge ([[electrical:12v:psoc|Partial State of Charge]], or PSOC) over time will result in [[electrical:batterycide|battery murder]]. |
| The reason for this is related to how lead-acid banks charge; they can take a ton of current in the first ~80% of charging (Bulk) then they hit a kind of wall. At that point you could drive 100mph or hook the bank up to the Hoover Dam's electrical output and it wouldn't finish charging significantly faster. | The reason for this is related to how lead-acid banks charge; they can take a ton of current in the first ~80% of charging (Bulk) then they hit a kind of wall. At that point you could drive 100mph or hook the bank up to the Hoover Dam's electrical output and it wouldn't finish charging significantly faster. |
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| From ~80% to 100% (Absorption stage) charging requires little current but a long time holding at a relatively high voltage. So in our alt+solar scenario the alternator does the heavy lifting in first bit and then a small solar install does the light (but lengthy) work at the end. | From ~80% to 100% (Absorption stage) charging requires little current but a long time holding at a relatively high voltage. So in our alt+solar scenario the alternator does the heavy lifting in the beginning then a small solar install does the light (but lengthy) work at the end.((The solar will also contribute during Bulk when the sun is shining.)) |
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| ===== how alternator charging helps ===== | ===== how alternator charging helps ===== |
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| Solar power is relatively weak compared to alternator charging. Solar is most challenged when the bank is deeply discharged and needs a large supply of current (early [[electrical:12v:charging#bulk_stage|Bulk charging]]). Alt charging shovels current into the bank up to the point that alternator voltage (Valt) is reached. | Solar power is relatively weak compared to alternator charging. Solar is most challenged in the morning when the bank is deeply discharged. The sun is weak then but the bank needs a large supply of current (early [[electrical:12v:charging#bulk_stage|Bulk charging]]). |
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| [[electrical:solar:charge_controller#pwm|PWM]] controllers are especially hamstrung in this scenario; since they run the panels at battery voltage (Vbatt) they produce the least power exactly when the most power is required. By the time Valt is reached PWM controllers are able to produce meaningful power. | [[electrical:solar:charge_controller#pwm|PWM]] controllers are especially hamstrung in this scenario; since they run the panels at battery voltage (Vbatt) they produce the least power exactly when the most power is required. By the time Valt is reached PWM controllers are able to produce meaningful power. |
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| | Alt charging shovels current into the bank up to the point that alternator voltage (Valt) is reached. Solar can take it from there. A good metaphor might be a two-stage rocket: the alternator does the heavy lifting then the solar charging takes it to high altitude. |
| ===== when augmented charging works best ===== | ===== when augmented charging works best ===== |
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| ===== gotchas ===== | ===== gotchas ===== |
| A bare solenoid doesn't know/care about the state of either battery, only that the ignition is in the ON position. | |
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| When | ==== general issues ==== |
| - solar is charging/equalizing higher than ~15v; and, | |
| - the house and batteries are connected | **When the chassis and house batteries are connected**, deep cycle **charging voltages** (Vabs) from solar or other sources **will be passed to the chassis**. Since charging voltages differ((lithium typically the lowest ~14.2v, around ~14.4v, and flooded the highest ~14.8v) this could be an issue if house batteries were flooded; flooded starter batteries would require more frequent watering. "Maintenance-free" sealed flooded batteries might be expected to fail earlier due to water loss. AGM starter batteries might be overcharged by flooded charging voltages, though voltage drop across the relay and inter-battery wiring may serve to attenuate that possibility. |
| the chassis' electrical system can be damaged by the overvoltage. When manually equalizing ensure the systems are not connected. If your charge controller does automatic EQ try to disable that feature. You may also want to [[electrical:12v:alternator_charging_hvd|automatically disconnect alternator charging]] when house battery voltage rises beyond a given setpoint. | |
| | If overvoltage is a concern, one can use one of these workarounds: |
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| | * disable automatic [[electrical:12v:charging#equalization|Equalization]] (EQ); or |
| | * decrease EQ voltage((Vequal))/duration; or |
| | * [[electrical:12v:alternator_charging_hvd|automatically disconnect alternator charging]] when house battery voltage rises beyond the starter battery's preferred charging voltage. |
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| | ==== voltage sensing relays ==== |
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| | [[electrical:12v:electrical:12v:alternator#voltage-sensing_relays|Voltage sensing relays]] can [[http://bdp.mousetrap.net/index.php/2018/10/27/side-effect-of-solar-alternator-charging/get "stuck connected"]] if the alternator and solar were charging the same time. This situation would exist until the sun when down and house voltage dropped below the VSR's disconnection setpoint. |
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| | It is effectively the same issue as the issue above. Workarounds: |
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| | * any a workaround from the list above; or |
| | * use [[electrical:12v:alternator#constant-duty_solenoid|a plain solenoid]] that would disconnect when the vehicle's key is turned off |
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