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opinion:frater_secessus:lifepo4_charging_voltage [2023/06/28 22:53] frater_secessus [Problems caused by excessive LiFePO4 charging voltage] |
opinion:frater_secessus:lifepo4_charging_voltage [2023/07/21 23:11] frater_secessus [Problems caused by excessive LiFePO4 charging voltage] |
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- | ====== Problems caused by excessive | + | ====== Problems caused by lithium charging profiles ====== |
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+ | ===== excessive charging voltage ===== | ||
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* voltages in the system are spiking, perhaps tripping your inverter | * voltages in the system are spiking, perhaps tripping your inverter | ||
- | It's fairly common for **excessive charging voltage** to cause these symptoms. | + | It's fairly common for **excessive charging voltage** to indirectly |
===== TLDR ===== | ===== TLDR ===== | ||
- | If this is the problem then reducing the charging voltage | + | If this is the problem then reducing the charging voltage will cause the symptoms to improve |
- | [[[opinion: | + | [[opinion: |
===== the full process ===== | ===== the full process ===== | ||
- | - reduce charging voltage (aka " | + | - reduce charging voltage (aka " |
- | - observe for a few days. Charging will be slower and may not finish by sundown((you may have to define or increase an Absorption/ | + | - observe for a few days. Charging will be slower and may not finish by sundown((you may have to define or increase an Absorption/ |
- | - if they do clear up you can start to raise the charging voltage back up gradually (13.65v, 13.7v, 13.74v, etc) or you can leave it low. {note from secessus: | + | - if symptoms |
- | - if it starts acting up again drop charging voltage back down | + | - if it starts acting up again drop charging voltage back down a notch or two |
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+ | ==== why lower-voltage charging works ==== | ||
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+ | LiFePO4 will fully charge at voltages as low as the mid-13s, | ||
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+ | * ≥14.0v will charge to 100% SoC with zero minutes of absorption durations: hit the voltage setpoint and //stop//. Cell voltages tend to diverge as charging voltage increases above 14.0v because they are further up the knee (see below) | ||
+ | * 13.8v will charge to 100% SoC with a small amount of Absorption (10-30 minutes?) and cells tend to stay in balance. | ||
+ | * 13.6v will charge to 100% SoC with several hours of Absorption | ||
+ | * 13.4v will // | ||
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{{ https:// | {{ https:// | ||
- lithium cell voltages are very " | - lithium cell voltages are very " | ||
- | - when one cell hits overcharge | + | - when one cell hits the knee first it can "run away" voltage-wise, |
- | - the BMS sees the runaway and shuts down charging to avoid damaging the cell | + | - the BMS sees the runaway and shuts down charging to avoid damaging the cell((if the charging is gentle enough the BMS may be able to stop the runaway by " |
- which stops **all** charging of the battery((and a voltage spike because the charger "went away", from the charger' | - which stops **all** charging of the battery((and a voltage spike because the charger "went away", from the charger' | ||
- | - if the cell imbalance is bad enough the battery can't charge anywhere near full because the misbehaving cell is causing | + | - if the cell imbalance is bad enough the battery can't charge anywhere near full because the misbehaving cell is causing |
So we ease up on charging which encourages the cell to stay in line with the others, which allows for a full battery charge. | So we ease up on charging which encourages the cell to stay in line with the others, which allows for a full battery charge. | ||
- | The bigger question is this: [[electrical: | + | The bigger question is this: [[electrical: |
- | ]] | + | |