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electrical:12v:drop-in_lifepo4 [2024/02/11 10:50] frater_secessus [myth: you have to charge Li to 100%] |
electrical:12v:drop-in_lifepo4 [2024/02/11 12:22] frater_secessus [myth: you can't use a combiner to charge batteries of different chemistries] |
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There are two different challenges here: | There are two different challenges here: | ||
- | - **different resting voltages** - if the lead rests at 12.8v and LiFePO4 at 13.6v then when charging stops the lead batt would put a drain on the li batt. | + | - **different resting voltages** - if the lead rests at 12.8v and LiFePO4 at 13.6v then when charging stops the lead batt could put a drain on the li batt. |
- | - **acceptable charging voltages** - the alternator voltage needs to be acceptable (not necessarily // | + | - **acceptable charging voltages** - the alternator voltage needs to be acceptable (not necessarily // |
=== acceptable charging voltage ranges === | === acceptable charging voltage ranges === | ||
- | We can assume the alternator voltage is acceptable to the starter battery because the manufacturer designed that system.((and we can observe that the vehicle starts on demand)). | + | We can assume |
- | For these examples | + | For the following thought experiment |
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- | Connecting during *charging* is typically a non-issue if the alternator output voltage is tolerable for those. | + | |
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- | * flooded lead acid typically *requires* >14.6v and gel typically *requires* <14.3v so those two won't play well together. | + | |
- | 1. they remain connected when charging stops -- the split relay is there to stop that from happening | + | |
+ | ^ Chemistry | ||
+ | | Gel | 14.0v - 14.3v | 14.2v | | ||
+ | | AGM | 14.2v - 14.5v | 14.4v | | ||
+ | | Flooded | ||
+ | | LiFePO4 | ||
+ | Let's think about some combinations. | ||
+ | * **easy to meet charging requirements by alternator alone** | ||
+ | * starter battery + LiFePO4. Charging LFP at 14.2v is a good balance between moderate voltage and charging time. Lithium is not affected by [[electrical: | ||
+ | * **unlikely to meet charging requirements by alternator alone** - could theoretically meet charging by alternator alone //if// given sufficient time. Unfortunately most people don't drive enough hours ((typically 5-6 hours from 50% SoC)) to complete Absorption; | ||
+ | * starter battery + AGM. 14.2v from the alternator is in the acceptable range, but just barely. | ||
+ | * starter battery + Gel. The alternator is putting out the exact Vabs spec'd by the manufacturer. | ||
+ | * **Useful but impossible((practically)) to meet charging requirements by alternator alone ** - cannot reach Vabs in any case. Solar is nearly mandatory, although DC-DC charging will do it if one is driving many hours a day. | ||
+ | * starter battery + flooded. | ||