Using Parallel Joined Lipo Batteries

This chapter assumes a basic familiarity with the principles of joining batteries in series and parallel. If these concepts are not already clear, the Gibbs Guide Electricity for Modelers will make these ideas easy to understand and is a recommended read.

An example of a parallel-joined lipo battery is where two 2200mah 3s lipo are joined to make a 3S battery of 4400mAh in capacity.

A suitbale wiring harness would be required for this. It is vital that before connecting packs in parallel that they are in an extremely similar state of charge. If a significant voltage difference exists when they are joined, a current will flow from the higher voltage battery into the other one until their voltages become identical. This current could be quite high because of the extremely low resistance in the circuit.

Charging parallel joined packs

It is possible to charge parallel joined packs while they are connected together. This would also be considered an experimental process and cannot be recommended. It is safest to charge parallel joined packs individually, joining them only when they are needed for use.

When connecting your batteries in Series you are doubling the voltage while maintaining the same capacity rating. When connecting in Parallel you are doubling the capacity (amp hours) of the battery while maintaining the voltage of one of the individual batteries.

So 2 x 6S 2500mah = 6S 5000mah

2 x 3S 5000mah = 6S 5000mah.

Personally fitting 5000mah 2s lipo in any truck would be very annoying plus the cost of a 6S battery far trumps the cost of a 3S. Go with 2 x 3S in a series.

Storage of parallel-joined cells

Since cells cannot be guaranteed to behave identically, it is safest to store parallel joined packs individually, joining them only when they are needed for use.

Unequal capacities

It’s not recommended to join packs of unequal capacity in parallel. In theory, it should be possible to quite safely do this. Because of the way the cells are connected, they will always remain at identical voltages, so the cells could theoretically still be expected to discharge evently in terms of percentage capacity remaining.

In practice, if discharging occurs at a high rage any differences in their internal resistance may cause the batteries to become unequally discharged. Therefore, cells of substantially unequal capacity which are joined in parallel should only be discharged at a relatively low current. Practically, this means its best not to join cells of substantially different capacity if they are to be used for flight packs. If you are in doubt about whether this issue applies to your model, a test is easy to arrange - connect the fully charged batteries in parallel, run the motor for a while and then disconnect the batteries. If there is a significant difference in voltage, this is evidence of unequal discharge.