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electrical:12v:drop-in_lifepo4 [2023/12/17 15:20] frater_secessus [but that Victron video] big dcdc |
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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* Li is relatively expensive | * Li is relatively expensive | ||
* Li cells need a [[# | * Li cells need a [[# | ||
- | * Li can be **damaged** by long duration at full charge or full discharge. | + | * Li can be **damaged** by long duration at full charge or high voltage, or high ambient temperatures |
* the flat voltage curve makes gauging SoC by voltage extremely challenging, | * the flat voltage curve makes gauging SoC by voltage extremely challenging, | ||
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Charging Li at very high rates may also strain the [[electrical: | Charging Li at very high rates may also strain the [[electrical: | ||
+ | |||
+ | ==== myth: you can't use a combiner to charge batteries of different chemistries ==== | ||
+ | |||
+ | 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 could put a drain on the li batt. The [[electrical: | ||
+ | - **acceptable charging voltages** - the alternator voltage needs to be acceptable (not necessarily // | ||
+ | |||
+ | === 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)). | ||
+ | |||
+ | For the following thought experiment we will use some a typical alternator output voltage of 14.2v and house bank charging voltage [[electrical: | ||
+ | |||
+ | ^ 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. | ||
+ | |||
+ | |||
==== myth: you have to charge Li to 100% ==== | ==== myth: you have to charge Li to 100% ==== | ||
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* 92A out of the 90A alt at reduced RPM. 184C at the coils.((6: | * 92A out of the 90A alt at reduced RPM. 184C at the coils.((6: | ||
- | At this point they disconnect the load and battery charge acceptance | + | At this point they disconnect the load and battery charge acceptance |
- | At 11:45 he re-applies the artificially | + | At 11:45 he re-applies the artificial |
**DC-DC chargers are good enough technology that there is no need to trick customers into buying them. ** | **DC-DC chargers are good enough technology that there is no need to trick customers into buying them. ** |