Released on Oct. 31, 2022
Yes, lithium polymer batteries can be connected in parallel. Parallel charging lithium polymer batteries allows multiple lithium polymer batteries to be charged at once using a single high quality battery. This will allow the batteries to get more runtime in a variety of specified electronic devices while reducing charging costs. For your LiPo batteries you should consider placing them on a parallel charging setup to increase their runtime and save time.
When used on LiPo batteries, parallel charging is known as polarisation and is much riskier as they are prone to errors. Not following the correct steps or skipping individual steps can lead to battery failure or damage.
Before connecting or charging lithium polymer batteries in parallel, you need to follow the rules and regulations below to ensure the safety of you and your batteries.
It does not matter whether you are conducting your experiments in a secluded building, in the open or even how you plan to perform the procedure. It is best to take the necessary precautions and ensure that a fire extinguisher is nearby, as anything can go wrong, from a faulty battery to an uncontrolled ignition of a flame. Lithium polymer batteries are not invincible. Also, make sure you perform items in metal/ammunition while charging to prevent fire spreading to the surrounding area.
Checking capacity and crates
It's never a big deal to charge different brands and capacities of batteries in parallel. However, you can never be too careful and need to ensure maximum. This requires you (as recommended) to charge LiPo cells of similar specification and with capacity and C ratings within a reasonable range.
Identical cell counts
Ensure that the LiPo batteries you intend to charge have the same cell count. This means that you should never charge a 3S cell with a 4S cell. A 3S cell must be charged with a 3S cell and a 4S cell with a 4S cell.
Checking the voltage
Always check the voltage of each cell using a LiPo voltage checker or reader before charging the cells in parallel. These will help you to identify batteries that should not be included in the process due to their very low voltage, thus allowing you to select them.
Avoid charging unhealthy batteries
When charging lithium polymer batteries, never charge unhealthy cells because of the risk of fire. Such cells should be disposed of properly. During parallel charging, a distorted cell can cause internal resistance within the cell, which in turn can significantly increase the temperature and cause a loss of control, leading to a fire.
Checking the charging current
For safety reasons it is recommended that you charge your LiPo pack at 1C. The charging current is usually calculated by multiplying the C rating by the capacity: Current = 1C * Capacity.
Connecting the balance leads
When charging LiPo batteries in parallel, always use the balance lead, which is somewhat similar to charging the battery separately. The reason for this is to prevent the intended charger from overcharging a particular battery.
Monitoring the battery while charging
Never leave a LiPo battery unattended while it is being charged (especially when connected in parallel). Monitoring the battery allows you to notice specific signs that should not be present during charging and that pose a significant risk of danger. These signs include cells overheating, swelling and even crackling sounds at certain times.
Charging the battery
Ensure that the following steps are carried out for the latter, otherwise permanent damage to the cells or the risk of fire may result
1. Connect your parallel plate charger
The first step is to connect the parallel charging board to the designated charger for the process. Most boards come with pre-installed banana plugs that can be placed into the charger to remain stationary. Unplug the cable from the charger and connect the board's wires to its location. Ensure that the terminals are properly connected to the separate positive terminal and to the negative terminal only. Once this has been done, plug the balance cable from the circuit board into the correct connector on the charger.
2. Turn on the charger
Power on the charger and ensure that it turns on in the correct way without displaying any errors or warnings.
First, discharge the leads of all the batteries and then balance them
Connect the batteries to the parallel charging board one at a time and ensure that the discharged leads of each battery are inserted first and then the balancing cable. Make sure you insert the balancing cables slowly and correctly as it is easy to inadvertently brush the wires through the wrong port and thus cause a spark. It helps if you are slow and steady and take the time to connect each balancing lead one after the other. While the order of the leads is not an issue, the orientation of the connectors is important, so make sure you adhere to this.
3. Determine the charge rate
Many of these modern LiPo batteries are able to accommodate high charge rates, but the recommended rate is always 1C. As mentioned above, in the rules and regulations above, you will need to calculate the charge rate before charging the battery. If the batteries have different mAh capacities, you will need to add them together and divide by 1000.
4. Enter the charger settings
Set the charger to the "Balance charge" option, select the battery type, the number of batteries and recheck to ensure that every detail is correct. Use the number obtained in the previous step as the charge rating.
5. Start charging the batteries
Once you have approved the settings, let the charger start charging and you should always be close enough to monitor the process in case there are any problems. Look out for any signs of abnormal occurrences, such as overheating, as LiPo batteries should never be warmer than their surroundings. They should also not produce any odours.
6. Remove the battery when charging is complete
Once the charger indicates that the charging process is complete, remove the batteries as they should all have the same voltage.
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