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opinion:frater_secessus:agm2lifepo4 [2024/10/07 11:16]
frater_secessus [shore power charging] moved low tep |
opinion:frater_secessus:agm2lifepo4 [2025/02/19 12:20] (current)
frater_secessus [Can I still use my existing DC-DC charger for alternator charging?] changed language |
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| ====== Upgrading an AGM house bank to LiFePO4 ====== | ====== Upgrading a lead-chemistry house bank to LiFePO4 ====== |
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| The pre-made LiFePO4 batteries (LFP hereafter) you seen on Amazon and elsewhere are designed and marketed as //drop-in replacements//: pull your lead battery and "drop in" the LFP. This approach works in many cases because the size, shape, voltage range, and charging requirements are in the same ballpark as traditional lead batteries. It's not a perfect scenario, but will meet the needs of the average user. People with special requirements or an interest in technical details can do the reading/testing required for an optimal setup. | The pre-made LiFePO4 batteries (LFP hereafter) you seen on Amazon and elsewhere are designed and marketed as //drop-in replacements//: pull your lead battery and "drop in" the LFP. This approach works in many cases because the size, shape, voltage range, and charging requirements are in the same ballpark as traditional lead batteries. It's not a perfect scenario, but will meet the needs of the average user. People with special requirements or an interest in technical details can do the reading/testing required for an optimal setup. |
| * 1.0C - typical limit enforced by BMS | * 1.0C - typical limit enforced by BMS |
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| From the battery's point of view, alternator charging rates should be ≤0.5C, with 0.4C likely being the sweet spot. So ≤80A for a 200Ah bank. From the alternator's point of view, current should be no greater than [[electrical:12v:alternator_details#current|the alternator can comfortably provide]] under expected charging conditions. | From the battery's point of view, alternator charging rates should be ≤0.5C, with 0.2C((for [[opinion:frater_secessus:lifepo4_charging_voltage|high charging voltages]])) to 0.4C((moderate charging voltages like 13.8v / 3.45Vpc)) arguably a sweet spot. So ≤80A for a 200Ah bank. From the alternator's point of view, current should be no greater than [[electrical:12v:alternator_details#current|the alternator can comfortably provide]] under expected charging conditions. |
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| As the Battle Born quote above suggests, for average LFP banks and average cargo van alternators these criteria will often be met with no reconfiguration. If the criteria cannot be met then we will need [[electrical:12v:b2b|DC-DC charging]] or some other approach to manipulate voltage and/or current.((diode-based isolator, dedicated second alternator, etc)) | As the Battle Born quote above suggests, for average LFP banks and average cargo van alternators these criteria will often be met with no reconfiguration. If the criteria cannot be met then we will need [[electrical:12v:b2b|DC-DC charging]] or some other approach to manipulate voltage and/or current.((diode-based isolator, dedicated second alternator, etc)) |
| If it was already handling a similar-size AGM bank then it will probably be fine. | If it was already handling a similar-size AGM bank then it will probably be fine. |
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| Caveat: charging LFP with DC-DC //can// be somewhat harder on the alternator than charging AGM with DC-DC. AGM current acceptance tapers in Absorption which means the DC-DC will not be demanding full powah from the alternator. Depending on the setup Lithium can make the "full pull" until the bank is near full charge. In practice this might only make a real difference with long drives and heavily discharged batteries. | Caveat: charging LFP with DC-DC //can// be somewhat harder on the alternator than charging AGM with DC-DC. AGM charging current spends less time at full charging current because it spends less time in Bulk (full current) and more in Absorption (tapering current). Depending on the setup Lithium can make the "full pull" until the bank is near full charge. |
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| An esoteric caveat: it's conceivable there are edge cases where a vandweller has an oversized DC-DC charger (60A?) that has not destroyed a small alternator (90A?) yet because the small lead bank (100Ah?) has only been pulling a fraction of the alternator's capabilities. Shoehorning in a 300Ah LFP bank would max the 60A charger and place serious demands on the undersized alternator. | An esoteric caveat: it's conceivable there are edge cases where a vandweller has an oversized DC-DC charger (60A?) that has not destroyed a small alternator (90A?) yet because the small lead bank (100Ah?) has only been pulling a fraction of the alternator's capabilities. Shoehorning in a 300Ah LFP bank would max the 60A charger and place serious demands on the undersized alternator. |
