to mark as completed Reversing the Polarity on LiPo Battery JST Connectors
The 2-Pin JST-PH 2.0 connector is found on many LiPo batteries used in hobby drones, RC cars and toys, and of course electrical boards and modules. These are handy little connectors, but there is one problem - the polarity convention. About half of the vendors connect the negative (black wire) on the left and the positive (red wire) on the right sides. The other half does it the other way around. This can be an issue if the board or electronics you want to plug the LiPo battery into has the reversed polarity convention. Plugging in the LiPo terminals backwards can cause damage to onboard components on many boards that do not have reversed polarity protection. It is easy to reverse the polarity on these JST connectors.
TL;DR
Check out our video on how to reverse the polarity of JST connectors commonly used on LiPo batteries.
Two Polarity Convention
JST connectors themselves have no indication which terminal should be designated as the negative and which is the positive. This decision is left for the manufacturer who inserts the crimped wires into the connector. For example, one particular manufacturer of a LiPo battery may assemble the battery terminal wires, most often red for positive and black for negative, black-red convention. Yet a different manufacturer assembles them the opposite convention, red-black. The two conventions are shown in Fig. 1.
This is a problem.
[Fig. 1 - Polarity convention for JST connectors. Left: black-red, Right: red-black.]
When inserting a LiPo battery into a board via the JST connector polarity often matters. There are many custom or specialized boards that do not have reversed polarity protection and inserting the positive and negative terminals may cause damage to onboard components.
NOTE: We found some user feedback on poorly made LiPo batteries where the black wire was NOT the negative terminal, and the red wire was NOT the positive terminal. The manufacturer had mistakenly attached the wires backwards. The best practice is to confirm the polarity with a multimeter.
The Method
The crimped wire has a small metal hook that latched under a flap on the JST connector, as shown in Fig. 2. The goal is to lift the flap up and away from the hook just barely enough so that the hook is free to slide underneath and out of the connector. Bending the flap too much, too aggressively, or even too many times will fatigue the joint where the flap attaches to the main body of the JST connector.
[Fig. 2 - Flaps and hooks on JST connector.]
We recommend using a small flat head screwdriver to lift the flap up. Using the flat head, there are two methods to lift the flap up.
- Come in from the side (Fig. 3), or
- Come in from the top (Fig. 4).
Both methods work, but we slightly prefer the coming in from the top method. This tends to leave less marks on the plastic body of the JST connector. This is also the method we show in our video.
[Fig. 3 - Method 1, come in from the side.]
[Fig. 3 - Method 2, come in from the top.]
If doing Method 1, then then we suggest to use a rotating movement of the screwdriver so that the flap is naturally lifted up by the side of the flat head that is furthest away from the joint of the flap to the body.
If doing Method 2, we suggest to first apply a small inward force so that the wire moves into the JST connector as deeply as possible (without bending, crushing, etc). The crimped wire tends to have about a 1mm jiggle when it is inside the connector. So extend that jiggle so that the wire is deeply inserted. This causes a small gap between the hook and the flap, which is just enough for the flat head screwdriver to get into. This part really is best to view in the video!
The next part is more or less a user preference. We prefer to hold the wire that is to be removed between the middle finger and the thumb. Gently pulling these towards the hand while using the index finger to press up against the JST connector causes a slight tension between the wire and the connector. When the flap is lifted just enough, the wire will pull out.
An that's really it! One last thing to remember is when reinserting the wires into the JST connector to make sure the wire is rotated such that the hook on the crimp is up (so that the flap can re-latch onto it). If one pushes the wire with enough force the wrong orientation, it will go into the connector, but it will be incorrect.
For good measure, we use the flat head screw driver to gently press down on the flaps after reinserting the wires just to make sure the flaps are latching well. A quick inspection of the JST connector is done to make sure no damage was done and the integrity of the connector remains.
Conclusion
Reversing the polarity of a 2-pin JST-PH connector is a simple but delicate process that can prevent costly damage to your electronics. The key is patience and precision — lift the flap just enough to release the crimp, swap the wires, and reinsert them in the correct orientation. Always verify polarity with a multimeter before plugging a LiPo battery into any board, especially those without reverse-polarity protection. With careful handling, your JST connector polarity can be safely reversed and the connector used on boards and modules that have either polarity convention.
Resources
PTSolns website: https://ptsolns.com
PTSolns Documentation Repository: https://docs.ptsolns.com
PTSolns Newsletter: http://eepurl.com/hnESjL