Why Are My Parallel Batteries Not Discharging Equally?
Why Are My Parallel Batteries Not Discharging Equal?
This is a very common and typical occurrence.
Even the slightest disparities in internal cell voltages, state of charge, cell resistance, BMS resistance, and even the voltage drop of the mosfets can result in the two separate battery strings carrying different amounts of current.
However, in real-world situations, it shouldn't pose a problem as long as you plan accordingly. When current is drawn, one battery supplies more power. This causes that battery to discharge slightly faster, and eventually its internal voltage will drop to the point where the other battery starts to carry more of the load. After that point, the cells will self-balance. With LFP cells, voltage changes occur gradually, so it may take some time for the balance to be achieved.
Can I Charge 2 12v Batteries In Parallel?
Generally, Charging two 12v batteries in parallel is possible, but not ideal as the batteries may not reach full charge simultaneously. This can result in one battery being slightly overcharged while the other is somewhat undercharged.
How Do You Charge Batteries In Parallel?
To charge batteries in parallel, you need to connect the negative terminal of one battery to the negative terminal of the next, and similarly connect the positive terminals. This setup maintains consistent voltage while increasing the overall capacity by utilizing the leads of each battery terminal.
Is It Better To Charge Batteries In Series Or Parallel?
Parallel battery configuration helps increase the duration in which batteries can power equipment, but due to the increased amp-hour capacity they can take longer to charge than series connected batteries. This time can safely be reduced, without damaging the batteries, by charging faster.
What Are The Problems With Charging Batteries In Parallel?
Charging batteries in parallel can lead to issues if the batteries are not well-matched, potentially resulting in overcharging or over-discharging, which can pose safety hazards. To mitigate these risks, it is advisable to utilize a dedicated battery management system when charging batteries in parallel to ensure even charging and discharging.
What Does It Mean For Lithium Batteries To Be Balanced?
Balancing lithium batteries involves ensuring that all individual cells or cell groups within a battery, or across multiple batteries in a system, maintain consistent voltage levels. This is crucial for maximizing the efficient utilization of the battery's total capacity and extending its lifespan by preventing overcharging or over-discharging of individual cells.
Possible Contributing Factors For Unbalanced Battery Charging And Discharging:
* The number of parallel-connected batteries exceeds the limit.
* Differences in brand, model, and capacity of parallel-connected batteries.
* Significant voltage differences before parallel connection of batteries.
* Different wiring methods, specifications, and lengths of parallel-connected batteries.
* Current differences due to relatively small charging or discharging currents.
Troubleshooting Steps For Unbalanced Battery Charging And Discharging:
This troubleshooting guide applies to the following products:
12V 100Ah Lithium Iron Phosphate Battery w/ Bluetooth View more 
Open Box 12V 200Ah Lithium Iron Phosphate Battery w/ Bluetooth View more
* Exclude the impact of the parallel connection limit. Confirm that the battery has fewer than 8 parallel-connected batteries.
------Possible Results------
Positive: Exceeded the quantity limit. Please remove excess batteries.
Negative: Within the quantity limit. Please try other steps.
* Exclude the possibility of mixed parallel connection. Confirm with the customer whether the parallel-connected batteries are identical, including brand, model, capacity, and voltage level.
------Possible Results------
NO. Inform the customer that mixing different batteries in parallel can lead to this issue.
YES. Please try other steps.
* Exclude the possibility of inconsistent initial battery voltages before parallel connection. Confirm with the customer whether the battery voltages were consistent before parallel connection.
------Possible Results------
Positive: Inconsistent battery Voc before parallel connection. Advise the customer to individually charge each battery to ensure Voc differences are less than 0.1V before parallel connection.
Negative: Please try other steps.
* Exclude the possibility of non-standard parallel connection. Ask the customer to provide actual wiring photos between the batteries and confirm the following:
- Whether the wiring method conforms to the official standard (as shown in the diagram).
- Whether the wire lengths are consistent.
- Whether the wire AWG (American Wire Gauge) is consistent.
- Whether the connections are secure.
------Possible Results------
Positive: Does not meet all the above requirements simultaneously. Please rewire according to the specified requirements.
Negative: Meets all the above requirements simultaneously. Please try other steps.
* Exclude the influence of small charging and discharging currents. Request screenshots from the customer's DC Home to determine if the normal charging and discharging currents are less than 0.2C.
Background Knowledge: In modern industrial production, it is challenging to produce batteries with completely consistent internal resistance. Inconsistent internal resistance in batteries + small charging and discharging currents = SOC/Voc imbalance, which is considered a normal phenomenon.
* Background Knowledge: What is C?
For a 100Ah battery, 1C = 100A, 0.5C = 50A, 0.2C = 20A.
For a 200Ah battery, 1C = 200A, 0.5C = 100A, 0.2C = 40A.
------Possible Results------
Positive: Charging and discharging currents < 0.2C. Increase the charging and discharging currents to resolve the unbalanced charging and discharging issue.
Negative: Charging and discharging currents > 0.2C. Please try other steps.
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