Batteries

3.7 V, 7.4 V, 11.1 V, 14.8 V, …​ - This is the nominal voltage of the battery. This can also be used to calculate the number of series cells on a battery, as a single cell has a nominal voltage of 3.7 V. When the battery voltage drops significantly below the nominal voltage, you can consider the battery to be empty. You can consider this threshold to be something like 3.5 V per cell. So 7 V for 2-cell battery, 10.5 V for 3-cell battery, 14 V for 4-cell battery. A full battery actually has a voltage higher than the nominal voltage of the battery: 4.2 V per cell. So it makes 8.4 V for 2-cell battery, 12.6 V for 3-cell battery, 16.8 V for 4-cell battery.

1S, 2S, 3S, 4S, …​ - This is the number of LiPo cells the battery has connected in series. This can be used to calculate the nominal voltage of the battery, as every cell has a nominal voltage of 3.7 V.

1000 mAh, 5500 mAh, 3000 mAh, 4000 mAh, …​ - this is the capacitance of the battery. This means that a 1000 mAh battery can provide average current of 1000 mA for 1 hour, 500 mA for 2 hours, …​, until the battery is discharged completely.

15C, 20C, 34C, 80C, …​ - This number means the maximum discharge rate of the battery as a function of its capacitance. A 1000 mAh 10C battery can be discharged at a maximum of 1000 mAh * 10C = 10000 mA = 10 A rate. Sometimes discharge rates are shown as something like 15C - 25C, in which case 15C is the maximum continuous discharge rate, while 25C is the maximum burst rate.

Choose correct battery type (LiPo).

Choose correct program (LiPo balance).

Choose correct charging current (0.5C - 1C, depending on battery age).

Choose correct charging voltage (match battery nominal voltage and number of cells).

Connect battery main plug and balance plug. Take note of polarity (black wire should be negative).

Start the charge.

Ensure that at least one person is always in the room while the battery is charging.

Connect batteries with similar voltage. If the voltages are different then high currents might flow from one battery to another. Parallel charging boards that we are using have fuses that can protect from damage to the batteries or the boards themselves, but fuses might get damaged and need to be replaced. Check the voltages with battery alarms before connecting.

Connect all main (XT60) plugs first. Main connector can handle higher currents, in case the batteries happen to have different voltages, and you forgot to check that. Balance charging connectors might get damaged from the high currents.

Increase charging current based on the total capacitance or battery count if the batteries have same capacitance. If you charge one battery with 1 A, then charge two batteries with 2 A (1 A per battery). Otherwise, the charging will take too long and other teams might be waiting to use the charger.

Each charger channel has an output power limit of 50 W. For example, when charging the batteries at 4 A (1 A per battery), the charger will start limiting the current at 12.5 V (50 W / 4 A) and above and the charging will take more time. Current at 16V will be limited to 3.125 A (50 W / 16 V) , about 0.78 A per battery. If other teams do not need to use the charger, then it’s fine to use more than one battery charger channel.

Make sure they are set to a sensible threshold voltage (preferably 3.5 V)

Make sure you attach them in the correct direction (black wire goes to the negative terminal).

Make sure they make a noise when you attach them.

Use at all times when actively discharging/using the battery. Otherwise, you risk over-discharging the battery and ruining it.

Do not use while charging.

Remove alarm and unplug battery when not using the battery for a longer time period (more than one hour). If you leave the alarms on overnight, they draw a small amount of current from the battery and may over-discharge it.