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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 [2023/07/22 00:09] frater_secessus [lack of pseudo-float] |
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- | ====== Problems caused by excessive | + | ====== Problems caused by lithium charging profiles ====== |
+ | |||
+ | You'd think that a " | ||
+ | ===== excessive charging voltage ===== | ||
[[https:// | [[https:// | ||
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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 " | ||
- | - 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 it starts acting up again drop charging voltage back down | ||
+ | - 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/ | ||
+ | - if symptoms do clear up you can start to raise the charging voltage back up gradually (13.65v, 13.7v, 13.75v, etc) or you can leave it low if you are getting enough charge. | ||
+ | - if it starts acting up again drop charging voltage back down a notch or two | ||
- | ===== why the problem occurs | + | === why lower-voltage charging works === |
+ | |||
+ | |||
+ | LiFePO4 will fully charge at voltages as low as the mid-13s, | ||
+ | |||
+ | * ≥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 // | ||
+ | |||
+ | |||
+ | ==== why the problem occurs ==== | ||
{{ 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: |
- | ]] | + | |
- | ===== further reading | + | ==== further reading ==== |
* [[electrical: | * [[electrical: | ||
+ | |||
+ | |||
+ | ===== lack of pseudo-float ===== | ||
+ | |||
+ | So your charge controller isn't charging even though battery state of charge is dropping? | ||
+ | |||
+ | This can be intentional behavior, caused by a Li profile that | ||
+ | |||
+ | - charges to a high voltage (see above) | ||
+ | - then allows the battery to discharge until it hits the [[electrical: | ||
+ | - at which point it charges to the high voltage again... | ||
+ | - rinse and repeat until the sun goes down | ||
+ | |||
+ | During the discharge stage the controller will appear to stop working. | ||
+ | |||
+ | To avoid this problem. configure a " | ||