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food:refrigeration:power [2024/05/09 16:27] frater_secessus [days of autonomy] |
food:refrigeration:power [2024/05/09 17:55] frater_secessus [why think about it 24hr terms?] |
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===== TL;DR ===== | ===== TL;DR ===== | ||
- | * 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: |
- | * compressor fridges don't take a lot of current | + | * they will consume |
- | * but they will consume Wh (Watt-hours) over a 24-hour period | + | * you must have at least enough charging capacity |
- | * you must make power to charge the bank | + | * and have enough |
- | * and have enough bank to make it through periods where charging is absent | + | |
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The compressor only runs as needed. | The compressor only runs as needed. | ||
- | 60w x 0.33 duty cycle x 24 hours = **480Wh** required each day to run the fridge. | + | 60w x 0.33 duty cycle x 24 hours = **480Wh** required each day to run the fridge. |
===== battery bank capacity ===== | ===== battery bank capacity ===== | ||
- | The battery bank capacity is dependent on a few factors: | + | The battery bank capacity |
- | * how deeply the chemistry can be discharged (~50% for lead, ~80% for LiFePO4) | + | * how deeply the chemistry can be discharged (~50% for [[electrical: |
* nominal voltage (12.0v for lead, 12.8v for LiFePO4) | * nominal voltage (12.0v for lead, 12.8v for LiFePO4) | ||
* days of " | * days of " | ||
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* ≥**47Ah of LiFePO4** (480Wh / 0.8 depth of discharge / 12.8v nominal) | * ≥**47Ah of LiFePO4** (480Wh / 0.8 depth of discharge / 12.8v nominal) | ||
+ | In practical terms 100Ah of LFP is cheaper by the Ah than 50Ah, so we would probably round up to 100Ah. | ||
==== days of autonomy ==== | ==== days of autonomy ==== | ||
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* fully charging every third day = 141Ah | * fully charging every third day = 141Ah | ||
* etc | * etc | ||
+ | |||
+ | Many folks will round up from 141Ah of LFP to 200Ah since that is a common size (and even less expensive by the Ah). | ||
+ | |||
Note: the math is simple with LiFePO4, since it is not affected by [[electrical: | Note: the math is simple with LiFePO4, since it is not affected by [[electrical: | ||
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+ | LiFePO4 is easier to charge than lead; it is more efficient, usually faster, and failure to reach 100% will not affect the battery negatively. | ||
+ | |||
+ | Lead requires ~20% more energy to replace the same Wh/Ah, and takes many hours to charge fully. For this reason lead is best charged by a combination of [[electrical: | ||
+ | |||
+ | |||
+ | ==== charging from alternator ==== | ||
+ | |||
+ | The simplest case will be charging LFP from [[electrical: | ||
+ | |||
+ | Charging LFP [[electrical: | ||
+ | |||
+ | Assuming there is enough time (usually 5-6 hours) a lead bank can be charged by DC-DC alone. | ||
+ | |||
+ | |||
+ | ==== charging from the ciggy port ==== | ||
+ | |||
+ | Usually only an option for "power stations", | ||
+ | |||
+ | |||
+ | ==== charging from solar ==== | ||
+ | Charging from [[electrical: | ||
+ | You will need to [[electrical: | ||
+ | December in Belle Fourche has only 1.52 hours of FSE. It would take ~375w of panel((flat-mounted, | ||
+ | The good news is there would be excess solar harvest in the other months of the year: | ||
+ | Solar wattage 375 | ||
+ | Month Daily Wh Avg | ||
+ | Jan 574 | ||
+ | Feb 806 | ||
+ | Mar 1329 | ||
+ | Apr 1658 | ||
+ | May 1865 | ||
+ | Jun 2298 | ||
+ | Jul 2324 | ||
+ | Aug 1983 | ||
+ | Sep 1562 | ||
+ | Oct 1010 | ||
+ | Nov 641 | ||
+ | Dec 485 | ||
+ | Average 1378 | ||
+ | table based on the PVwatts link above | ||
+ | ==== charging from multiple sources ==== | ||
+ | Often [[electrical: | ||
+ | Adding 30mins of 30A DC-DC charging a day would drop the panel requirement to ~236W. | ||
+ | And since the solar would be handling higher-voltage / longer duration charging duties one could fall back to a less expensive [[electrical: | ||
+ | Or one could use [[electrical: | ||