In this article I want to talk a little bit about battery connectors. Battery connectors - you wonder? Yes! What might at first sound like a boring topic with not much to say, turns out to be a quite interesting one, especially when it comes to brushless whoops.
Every mechanical connection is a place where electrical energy can be “lost” - or to be physically correct - translated into heat. You want your plugs to be as lossless as possible, so that all the energy can reach the place where it should be used - mainly the motors.
This means the contact resistance of the plug should be as low as possible and the current rating as high as possible - of course relative to the needs of your quadcopter.
In the quadcopter hobby we are using different kinds of battery connectors. The type depends on the size of the model and thus the current draw. The bigger the batteries and the setup - the higher the current draw - the bigger has to be the battery connector.
Connectors all have a current rating - this current rating refers to how much power the plug can safely dissipate. This further means the current rating of a plug is independent of the voltage, but instead depends on the plugs internal resistance:
P = I² * R
Generally speaking this means you can safely push more current through a connector if you only do it for a short amount of time and the plug has some time to cool down - for example through high air flow, as we usually have when flying quadcopters.
If you push more current through the connector than it can handle (and dissipate), the connector will get hotter and at one point the wires will de-solder from the connector. This is obviously the worst case which don’t want to happen.
A clear sign of a “bad” or under-specced plug is, when you can feel it being hot after ripping a pack.
Lets take a closer look at the battery connectors currently most commonly used in the hobby, and some new, emerging options specially designed for whoops.
XT60 is the de-facto standard with models 3 inch and up. Before XT60 became popular, people often used the Deans or T-Plug. The nice thing about XT60 in comparison to Dean is, that both sides of the plug are protected against unintentional short circuit and it is much easier to plug and unplug.
XT60 is commonly used with the higher capacity 3S batteries and is pretty much standard with 4S and higher.
Technically the 60 in XT60 stands for the current the plugs are rated for. But in reality they can handle up to 180A of burst current and 120A continuous - should you exceed this current, you might want go with XT90, but XT60 should be plenty even for a 6 or 7 inch setup, and is definitely more than enough for 5 inch.
My goto XT60 plugs are the ones manufactured by Amass and they come with a nice cover over the solder cups, so no heat shrink is needed.
An XT60 connection - male and female plug - can weigh in at around 7.5g - obviously you would not want to use this with smaller scale models.
If you are using this connector at its limits, I would encourage you to use 12AWG wire - for normal use cases 14AWG is plenty.
XT30 is basically a scaled down version of XT60 and it is used with a lot of 2S batteries and some of the lower capacity 3S batteries.
The XT30 connector can easily handle 60A of continuous current when 16AWG wire is used. If you go with the manufacturer recommended 18AWG, you should not draw more than 45A continuously. Should you exceed this, go with XT60 instead.
My goto XT30s are again the original ones manufactured by Amass.
Be careful when buying XT30 connectors, and get those with solder cups, there is a variant for PCB mounting that just has pegs and you will not easily be able to make a solid connection to the wire with those.
An XT30 connection - male and female plug - weighs in at about 1.7g. Although the XT30 connector is a good choice for 2S builds, it will most probably not be the connector of choice for your 1S brushless whoop build.
This connector is also know as MCPX, JST mCP-X and , PH. It has gained big popularity in the brushless whoop world.
You have to be careful with this plug - it comes with different pin types - rolled (sometimes also called folded) and solid. You want to make sure to get the version with the solid pins.
Unfortunately, most models come with the rolled pin version, but the difference is night and day, the solid pin version allows so much more current to flow - it is as if you fly two completely different models.
The folded pin version will work well at the beginning, but over time it will degrade (the contacts will oxidize and the resistance will increase), you might think that your batteries start to sag, but in reality it is actually just the plug.
The current rating of this connector is 2A. That being said, a lot of people report being able to draw much higher currents with this connector using a 20AWG cable. This will only reliably work with the solid pin version though.
I highly recommend swapping your folded or rolled PH2.0 connector for one with solid pins. You will most probably have to look around to find those connectors, as far as I know, none of the Chinese sellers has them. I could not even find them on Amazon. You can source them from Digikey though.
The JST PH2.0 connector, male and female weighs in at just 0.22g. This makes it quite obvious, why it is the goto choice for 1S whoops.
Also known as JST, BEC or P connector.
This connector is rated for a continuous amp draw of 3A, many people feel comfortable pushing up to 5A continuously through this connector.
A JST RCY connection - male and female plug - weighs in at about 0.65g. Not the lightest option. Instead of using this connector, I would go with XT30 when using 2 cells and more or with the PH2.0 connector when using 1 cell batteries.
Micro Molex Connector (51005 Series)
This connector is also known as Lossi or Micro Lossi connector.
An important side-note here ist, that this connector comes with different polarities - so double check that the battery you are using has the same pin-out as the plug you will connect it to or you will have a bad time.
I am not a big fan of those connectors personally since the contacts are flat and tend to wear out quickly. They oxidize and then the connector easily gets hot. I once had one of those connectors melt in such a way that it shorted out the battery contacts.
Instead of using those I would highly encourage you to use a PH2.0 connector with solid pins instead, they are better in basically every single way.
The micro molex connection, male and female weighs in at 0.4g.
The BT2.0 connector is a proprietary connector by BetaFPV aimed at 1S batteries. This connector is capable of pushing up to 15A.
The BT2.0 connector, male and female weight in at 0.58g.
Unfortunately this connector is not very wide spread and you will have a hard time finding batteries that already come with this connector - except for the packs that are offered by BetaFPV directly.
This connector is definitely not one of the cheapest, and if you are planning on retrofitting your whoop batteries, the price of the connector is definitely something to consider.
Some people complain that this connector can easily be plugged in the wrong way around. This is not easily possible in my opinion, I mean you technically can plug them in the wrong way around, but you have to put some force into it, so I can’t really see this happen by accident.
This is GNB’s own battery connector. They came up with it, after BetaFPV did not manage to properly pitch the BT2.0 connector to GNB.
GNB being one of the biggest battery manufacturers for our hobby, clearly has a benefit when rolling out their own connector. Same as BT2.0 this connector is targeted as a replacement for the PH2.0 connector, allowing for more current to be pulled safely over this connector.
The GNB 27 connector, male and female weigh in 0.82g - almost 4 times the weight of the PH2.0 connector and significantly heavier than the BT2.0.
A lot of people have been looking forward to this connector, but I do not have the feeling that this connector is gaining popularity. Size-wise it is comparable to XT30 - and weight-wise it is just a bit too heavy for a 1S whoop build in my opinion.
The 27 in it’s name does not refer to the current, but rather the size of the connector, which is a strange choice in my opinion.
Unfortunately I can not find any current ratings for this connector, but I expect it to be around the same as the BT2.0 connector.
The weight is given for a pair of the connectors without a wire attached to them.
Current is the rated current for the plug.
Best battery connector for Whoops
In my opinion the best choice for 1S whoops is the PH2.0 connector with solid pins and 20AWG wire. You will have a lot of different battery choices with this connector and with the solid pins you can push enough amps to fill your 1S needs.
If you are going for a 2S whoop, I would highly recommend going with an XT30 connector.