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opinion:frater_secessus:self-heated_lifepo4 [2023/09/03 14:06] frater_secessus |
opinion:frater_secessus:self-heated_lifepo4 [2023/10/17 15:13] (current) frater_secessus [how the approaches work] |
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====== Self-heated vs DIY warming ====== | ====== Self-heated vs DIY warming ====== | ||
+ | ===== TLDR ===== | ||
- | ###TL;DR | + | * LiFePO4 cannot be charged when the cells are below ~freezing. |
+ | * some kind of warming is required before charging | ||
+ | * self-heated: | ||
+ | * DIY: more control, more charging under certain conditions, usually cheaper | ||
+ | * in practice, warming is combined with other forms of protection: | ||
+ | ===== how the approaches work ===== | ||
- | With " | + | **Self-heated batteries** |
- | With robust | + | - sense ~freezing temps |
+ | - shut off charging((normal BMS shutoff)) | ||
+ | | ||
+ | - when cell temps are >freezing | ||
+ | - optional: | ||
- | Outside cost considerations, | + | This means //warming only happens when charging is present// |
- | * how much charging would I miss out on because the bank is taking only 60w to run the heaters instead of taking everything I can throw at it?; and | ||
- | * how does this compare to the Wh required to keep the bank above freezing when no charging is present? | ||
+ | **DIY warming solutions** | ||
- | ### worst-case scenario | + | |
+ | - use the lowest-wattage warming mat practical | ||
+ | | ||
- | Imagine | + | This means //warming happens whether or not charging is present// |
+ | |||
+ | ===== when it's a wash ===== | ||
- | * freezing overnights followed by a half-hour drive in the morning with a 30A DC-DC. | + | |
- | * a battery with warming pad that consumed 60Wh overnight to stay above freezing, vs | + | With " |
- | * a self-heating battery that is below freezing in the morning | + | |
+ | |||
+ | ===== when self-heated might be preferable ===== | ||
+ | |||
+ | When you want a packaged solution. | ||
+ | |||
+ | If you run your bank very low habitually((stop doing that!)) and the warming load is enough to trigger BMS discharge shutdown. | ||
+ | |||
+ | |||
+ | ===== when DIY warming might be preferable ===== | ||
+ | |||
+ | ==== robust charging ==== | ||
+ | |||
+ | |||
+ | With robust charging (alternator and/or bigger solar) there can be charging opportunities lost with self-heated batteries in freezing conditions. | ||
+ | |||
+ | Imagine the following scenario | ||
+ | |||
+ | | ||
+ | * a battery with warming pad that consumed 60Wh overnight to stay above freezing, vs | ||
+ | * a self-heating battery that is below freezing in the morning | ||
The externally warmed bank accepts current immediately and takes **15Ah of recharge**. | The externally warmed bank accepts current immediately and takes **15Ah of recharge**. | ||
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With 50A charging it's 260Wh net vs 107Wh net. . | With 50A charging it's 260Wh net vs 107Wh net. . | ||
- | If one was charging by alternator only and only driving to/from work while stealthing in freezing weather it's conceivable the self-heated batt would get *never get charged at all* because it wouldn' | + | If one was charging by alternator only and only driving to/from work while stealthing in freezing weather it's conceivable the self-heated batt would get //never get charged at all// because it wouldn' |
+ | |||
+ | ==== specific configurations ==== | ||
- | ## counterpoint | + | You may want more control over the temperature setpoints. |
- | If one charged by solar this delay time is less important; | + | Note from Secessus: |
- | ### worst-case scenario for self-heated | ||
- | You run your bank very low habitually (don't do that) and the warming load is enough | + | ===== how to think about the decision ===== |
- | I don't know of any LiFePO4 that still has a single control channel for both charge/ | + | There is no one-size-fits-all solution but outside cost considerations, the essential questions are |
- | ### configurability | + | * how much charging would I miss out on because the bank is taking only 60w to run the heaters instead of taking everything I can throw at it?; and |
+ | * how does this compare to the Wh required to keep the bank above freezing when no charging is present? | ||
+ | * do I need greater | ||
+ | * do I have the interest or ability to DIY? | ||
- | Also a control issue; | + | ===== further |
+ | * [[https:// | ||