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electrical:12v:directcharginglfp [2022/11/05 12:29]
frater_secessus [Isolator charging LiFePO4 banks] |
electrical:12v:directcharginglfp [2023/01/28 11:58]
frater_secessus [Direct charging LiFePO4 banks] |
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| ====== Isolator charging LiFePO4 banks ====== | ====== Direct charging LiFePO4 banks ====== |
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| There is an [[electrical:12v:drop-in_lifepo4#mythyou_must_use_dc-dc_for_alternator_charging_li|often-repeated claim]] that LiFePO4 house banks will pull always monstrous levels of current and destroy alternators if a plain [[electrical:12v:alternator|isolator]] is used instead of a [[electrical:12v:b2b|DC-DC charger]]. This claim is not supported by empirical testing. The data below provide **actual measurements** to help people make informed decisions. We will see that **current demand by LFP banks follows a known formula** rather than the opinions of people on the internet. | There is an [[electrical:12v:drop-in_lifepo4#mythyou_must_use_dc-dc_for_alternator_charging_li|often-repeated claim]] that LiFePO4 house banks will always pull monstrous levels of current and destroy alternators if a plain [[electrical:12v:alternator|isolator]] is used instead of a [[electrical:12v:b2b|DC-DC charger]]. This claim is not supported by empirical testing. The data below provide **actual measurements** to help people make informed decisions. We will see that **current demand by LFP banks follows a known formula** rather than the opinions of people on the internet. |
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| Short digression: there is a related **claim that LiFePO4 cannot be charged fully by isolator**. Maybe, but... | Short digression: there is a related **claim that LiFePO4 cannot be charged fully by isolator**. Maybe, but... |
| {{https://img.mousetrap.net/misc/isolatorMaxCRate.jpg}} | {{https://img.mousetrap.net/misc/isolatorMaxCRate.jpg}} |
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| The average max current drawn from the alternator is **0.33C**, or 1/3rd of what the warnings predict. **This the same C-rate that AGM pulls when cycled to 50% DoD**. | The average max current drawn from the alternator is **0.33C**, or 1/3rd of what the warnings predict. **This the same C-rate that AGM pulls when cycled to 50% DoD**. You can use these C-rate reports as a way to ballpark what your own Li bank might pull. |
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| This crude and fictional graph illustrates the //general patterns of current demand// on the alternator from both isolators (purple) and DC-DC chargers (green). | This crude and fictional graph illustrates the //general patterns of current demand// on the alternator from both isolators (purple) and DC-DC chargers (green). |
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| The isolator starts out high at 85A and current starts falling off immediately. It continues dropping gradually as battery bank voltage comes up to 14.0v at about 30 minutes.((made up timeline)) Current continues to drop but **voltage is held at 14.0v unless the isolator is disabled**.((the green bump at the end is a typo I didn't catch until later -- secessus)) | The isolator starts out high at 85A and current starts falling off immediately. It reaches a kind of plateau in the "middle 80%", then tapers gradually as battery bank voltage comes up to 14.0v at about 30 minutes.((made up timeline)) Current continues to drop but **voltage is held at 14.0v unless the isolator is disabled**.((the green bump at the end is a typo I didn't catch until later -- secessus)) |
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| The DC-DC holds a steady 60A until the 14.4v setpoint is reached around 50 minutes. Current drops off steadily until Absorption durations times out at 100 minutes.((or however configured)). DC-DC drops to float 13.4v and current tapers away. | The DC-DC holds a steady 60A until the 14.4v setpoint is reached around 50 minutes. Current drops off steadily until Absorption durations times out at 100 minutes.((or however configured)). DC-DC drops to float 13.4v and current tapers away. |
