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opinion:frater_secessus:self-heated_lifepo4 [2023/09/03 13:42] frater_secessus created |
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 | + | DRAFT |
+ | ====== Self-heated vs DIY warming ====== | ||
+ | ===== TLDR ===== | ||
+ | * 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 ===== | ||
+ | **Self-heated batteries** | ||
- | > difference in efficiency vs a diy setup with | + | - sense ~freezing temps |
+ | - shut off charging((normal BMS shutoff)) | ||
+ | - allow incoming power only to the internal heaters, typically ~60w | ||
+ | - when cell temps are >freezing charging is re-enabled | ||
+ | - optional: | ||
- | It's not so much an efficiency issue as economics and charging | + | This means //warming only happens when charging |
- | The economics issue is straightforward; | ||
- | The charging opportunity issue is murkier. | + | **DIY warming solutions** |
- | * a battery with warming pad that consumed 60Wh overnight to stay above freezing. | + | - use an external temperature controller and temperature probe |
- | * a self-heating | + | - use the lowest-wattage warming mat practical for conditions((for gentlest, most-even |
+ | - and turn the mat on/off with the controller | ||
- | The externally warmed bank accepts current immediately and takes **15Ah of recharge**. | + | This means //warming happens whether or not charging is present//. |
+ | |||
+ | ===== when it' | ||
- | 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 *no charging at all* because it wouldn' | ||
- | ### counterpoint | + | With " |
- | If one charged by solar this delay time is less important; | ||
+ | ===== when self-heated might be preferable ===== | ||
- | ### configurability | + | When you want a packaged solution. |
- | Also a control issue; | + | If you run your bank very low habitually((stop doing that!)) and the warming load is enough |
+ | |||
+ | ===== 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 | ||
+ | |||
+ | * 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 | ||
+ | * a self-heating battery that is below freezing in the morning | ||
+ | |||
+ | The externally warmed bank accepts current immediately and takes **15Ah of recharge**. | ||
+ | |||
+ | The self-heated battery shunts 60w to the heater (leaving 10A of charging unused) until the warmth equalizes up to the temp sensors. | ||
+ | |||
+ | 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' | ||
+ | |||
+ | ==== specific configurations ==== | ||
+ | |||
+ | You may want more control over the temperature setpoints. | ||
+ | |||
+ | Note from Secessus: | ||
+ | |||
+ | |||
+ | |||
+ | ===== how to think about the decision ===== | ||
+ | |||
+ | There is no one-size-fits-all solution but outside cost considerations, | ||
+ | |||
+ | * 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 configurability than the built-in heater allows? | ||
+ | * do I have the interest or ability to DIY? | ||
+ | |||
+ | ===== further reading ===== | ||
+ | |||
+ | * [[https:// | ||