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food:refrigeration:power [2024/05/09 17:27] frater_secessus [charging from solar] |
food:refrigeration:power [2024/05/09 17:57] (current) frater_secessus [TL;DR] |
===== TL;DR ===== | ===== TL;DR ===== |
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* compressor fridges are a part-time load; as a rule of thumb we can assume the compressor will be running 1/3rd of the time. | * [[food:refrigeration#compressor_refrigeration|compressor fridges]] are a part-time load; as a rule of thumb we can assume the compressor will be running 1/3rd of the time. |
* but they will consume Wh (Watt-hours) over a 24-hour period | * they will consume a given number of Wh (Watt-hours) over a 24-hour period |
* you must make power to recharge the bank | * you must have at least enough charging capacity to replace those Wh |
* and have enough bank to make it through periods where charging is absent | * and have enough battery bank capacity to make it through periods where charging is absent |
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===== battery bank capacity ===== | ===== battery bank capacity ===== |
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The battery bank capacity is dependent on a few factors: | The battery bank capacity requirement is dependent on a few factors: |
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* how deeply the chemistry can be discharged (~50% for lead, ~80% for LiFePO4) | * how deeply the chemistry can be discharged (~50% for [[electrical:12v:deep_cycle_battery|lead]], ~80% for [[electrical:12v:drop-in_lifepo4|LiFePO4]]) |
* nominal voltage (12.0v for lead, 12.8v for LiFePO4) | * nominal voltage (12.0v for lead, 12.8v for LiFePO4) |
* days of "autonomy" (discussed separately) | * days of "autonomy" (discussed separately) |
The simplest case will be charging LFP from [[electrical:12v:b2b|a DC-DC charger]]. Using a 30A DC-DC as an example, it would take about 1.25 hours (75 minutes) of driving each day to replace 480Wh. 480Wh / [30A x 12.8v]) | The simplest case will be charging LFP from [[electrical:12v:b2b|a DC-DC charger]]. Using a 30A DC-DC as an example, it would take about 1.25 hours (75 minutes) of driving each day to replace 480Wh. 480Wh / [30A x 12.8v]) |
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Charging LFP [[electrical:12v:directcharginglfp|directly from the alternator]] with a combiner works but the time required is not strictly predictable. Charging current will be highest at low State of Charge and lowest at high SoC; this is called the "current taper".((the same taper occurs with lead, but combiner-only charging is not recommended for lead, as the voltage is typically too low)) | Charging LFP [[electrical:12v:directcharginglfp|directly from the alternator]] with a combiner works but the time required is not strictly predictable. Charging current will be highest at low State of Charge and lowest at high SoC; this is called the "current taper".((the same taper occurs with lead, but combiner-only charging is not recommended for lead, as the voltage is typically too low)) Bonus: combiners usually make [[electrical:12v:self-jumpstarting|self-jumpstarting]] trivially easy. |
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Assuming there is enough time (usually 5-6 hours) a lead bank can be charged by DC-DC alone. The long (and mandatory) Absorption period is the tail that wags the dog. | Assuming there is enough time (usually 5-6 hours) a lead bank can be charged by DC-DC alone. The long (and mandatory) Absorption period is the tail that wags the dog. |
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==== charging from the ciggy port ==== | ==== charging from the ciggy port ==== |
==== charging from solar ==== | ==== charging from solar ==== |
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Charging from [[electrical:solar:gentle_intro|solar]] is predictable((on average)) if one knows where/when one will be camping. Because December has the lowest insolation in the Northern hemisphere we base our panel requirements on that month. If you are not full-timing then use the month closest to winter solstice. | Charging from [[electrical:solar:gentle_intro|solar]] is predictable //on average// if one knows where/when one will be camping. Because December has the lowest insolation in the Northern hemisphere we base our panel requirements on that month. If you are not full-timing then use the month closest to winter solstice. |
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You will need to [[electrical:solar:pvwatts|calculate how much sun]] (hours of Full Sun Equivalent, aka "kWh/day") is available in your actual wintering spot, but we will use Belle Fourche, South Dakota since it is the geographical center of CONUS. | You will need to [[electrical:solar:pvwatts|use PVwatts or similar]] to calculate how much sun (hours of Full Sun Equivalent, aka "kWh/day") is available in your actual wintering spot, but we will use Belle Fourche, South Dakota since it is the geographical center of CONUS. |
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December in Belle Fourche has only 1.52 hours of FSE. It would take ~375w of panel((flat-mounted, MPPT controller, LFP bank)) to replace 480Wh year-around. (480Wh / 1.52 hours of FSE / 0.85 overall efficiency) | December in Belle Fourche has only 1.52 hours of FSE. It would take ~375w of panel((flat-mounted, MPPT controller, LFP bank)) to replace 480Wh year-around. (480Wh / 1.52 hours of FSE / 0.85 overall efficiency) |
Average 1378 | Average 1378 |
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| table based on the PVwatts link above |
==== charging from multiple sources ==== | ==== charging from multiple sources ==== |
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Adding 30mins of 30A DC-DC charging a day would drop the panel requirement to ~236W. This could mean easier mounting, a smaller [[electrical:solar:charge_controller|solar charge controller]], smaller-gauge wiring, etc. | Adding 30mins of 30A DC-DC charging a day would drop the panel requirement to ~236W. This could mean easier mounting, a smaller [[electrical:solar:charge_controller|solar charge controller]], smaller-gauge wiring, etc. |
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And since the solar would be handling higher-voltage / longer duration charging duties one could fall back to a less expensive [[electrical:12v:alternator#combiners|combiner]] for the alternator side. | And since the solar would be handling higher-voltage / longer duration charging duties one could fall back to a less expensive [[electrical:12v:alternator#combiners|combiner]] for the alternator side. The alternator doing the heavy lifting might mean one could use a less expensive PWM controller. |
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| Or one could use [[electrical:12v:b2b#examples_-_combo_with_solar_charge_controller|a combo DC-DC/MPPT controller]] that handles both charging sources in one unit. Some can also maintain the vehicle's starter battery from solar. |
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