This is one of those subjects that just baffles many pilots, new or seasoned. Many see it as some magical device that does nothing but cramp their style. If you are one of these baffled folks or even if you think you have it figured out, read on for an explanation of both what they are and the differences between the various types.
What is a balance connector?
A balance connector is nothing more than a breakout connector for accessing all the individual cells contained in a lipo. This allows for the monitoring and manipulation of each cell individually.
Why are balance connectors needed?
Like everything in the world, no two things are exactly the same, and batteries are no different. When multiple batteries, or cells, are assembled into packs, those different differences can lead to imbalances within the pack. In most cases, like NiXX cells, this is not a problem due to the chemistry of the cells. But when using lithium based cells, these imbalances can damage the cells and in some extreme cases even result in a fire.
Looking at how lipos are wired
As you can see this pack is composed of 3 cells wired in series. Then the main leads are connected to the outer most (-) and (+) tabs. The balance leads are connected at both the (-) and (+) of each cell. As such there will always be one more balance wire than the number of cells, in this case 4 wires for 3 cells.
The best way to understand how something it put together is to take it apart. Well I don't have any lipos to take apart to show you but I can draw you a diagram to illustrate it.
Monitoring and manipulating each cell
Finally it's time to get down to the real reason for having the balance connector, the ability to monitor and manipulate each individual cell. This ability exists because there is a wire going to the (-) and (+) of each individual call. As such you, or more often your charger, can use each pair to access a specific cell. For example below is the breakdown of cells (voltage) by color in the above photo when using a volt meter.
black -> yellow = cell 1 (3.7V)
yellow -> green = cell 2 (3.7V)
green -> red = cell 3 (3.7V)
black -> green = cells 1 + 2 (7.4V)
yellow -> red = cells 2 + 3 (7.4V)
black -> red = cells 1 + 2 + 3 (11.1V)
When a lipo's balance connector is plugged into a lipo balancer, the balancer can both monitor the voltage of each cell and if need be, discharge any high cells in order to balance the pack.
Other uses for the balance connector
Some chargers only charge through the balance connector. Many cheap oem chargers do this but some nicer models will also allow for it. In this case the charger is both charging and balancing through the balance connector.
Sometimes there is a need for a connection to a battery and you don't want to use the main leads. In that case you could use the balance connector for a low current draw connection. For example lets say you have a camera setup on a bird. Instead of wiring the power for camera system into the main bird, you could connect a separate bec to the balance connector on the battery in order to power this separate system.
Charging one cell through the balance connector
Since the balance connector has access to each cell, it is possible to charge each cell individually. All that is needed is an adapter and a charger that can charge single cells.
As you can see balance connectors are not magical at all. They simply break out all the individual cells in a lipo so you or the charger can monitor and manipulate each individual cell.
Explaining the differences between the various types
This is where balance connectors get irritating. Like cell phone chargers, battery companies seem to all have a proprietary balance connector on their lipos. What a waste if you ask me but that is just how it is. The good news, if there is such a thing, is that all balance connectors are attached to the same wires, they just arranged in different orders and ways.
The popular types
By my counting there are 3 popular balance connector types:
Thunder Power (TP)
There are a couple of other connectors but they are rare. One is Kokam but they appear to be very similar to JST-XH connectors, in terms of layout and wire order, but use a slightly different connector. Another is FMA Cellpro. Like TP, they have 2 connectors and use one or the other or both depending on how many cells are in a pack. These also use 2mm spacing and have a similar pin to the TP connectors but use a different housing and wire layout.
Now that the connectors have been defined, it's time to talk about the wiring. Like I said before, the wires going to each balance connector are all the same, save for the color. They all connect to the same places in each battery and all do the same thing.
I am not going to explain how every individual connector is wired up but instead I am going to two examples to get the basics across.
The above diagram shows how the
7 balance wires needed for a 6s
pack are connected to each
JST-XH connectors are by far the simplest. All the wires are simply attached in order starting with Neg (-) at the top of the connector and finishing with Pos (+) at the bottom. This is the case for all 2s-6s balance connectors.
Hyperion uses a 5-pin connector for 2s-4s, so in the case of 3s there is an unused pin in the connector. Unfortunately Hyperion fills the connectors by placing the Pos (+) at the bottom and then filling up from there. Then when it gets to the Neg (-) wire, it places it at the top. This causes the unused pins to be in the middle. In the case of 4s-6s batteries, all the pins in each connector are used making them essentially the same as JST-XH. In fact they can be interchanged.
Thunder Power (TP)
TP is the odd ball. In a way they are efficient because they only use 2 different connectors but this makes them more complicated when you get past 5s. For 2s-3s a 4-pin is used. A 3s pack uses all 4 pins and a 2s uses the first 3 and leaves the 4th unconnected. For 4s-5s the 6-pin is used. A 5s pack uses all 6 pins and a 4s uses the first 5 and leaves the 6th unconnected. For 6s-8s both a 4-pin and a 6-pin are used. An 8s pack uses all 10 pins (pins 4 of the first connector and pin 1 of the 6-pin connector are tied together), a 7s uses the first 9 and a 6s uses the first 8. Notice a trend? All TP connectors have all the wires in them but only connect the needed wires to the battery. The remaining wires are unused and are just along for the ride.
A quick note on the Cellpro balance connector wiring. Cellpro used 2 connectors, a 5-pin and a 6-pin. The 5-pin is used for 2s-4s packs. The 6-pin is used for 5s packs. Then 2 connectors are used for larger packs. All connectors are filled by placing the Neg (-) wire at the bottom of the connector and filling up from there. Then when it gets to the Pos (+) wire, it places it at the top. This is similar to how Hyperion does it but just backwards, starting with Neg (-) at the bottom instead of the top.
As you can see all balance connectors use the same wires but just use them differently. As such you can rewire any pack to work with any balance connector.
Adapting and converting between the various types
Due to the fact that most of us are not going to use a single brand of lipo or that out lipos very likely won't match the charger we use, we are forced to buy/make adapters.
Changing out the connector
Many times it is best to have just one type of connector on all of your batteries. Some do this by always buying the same brand of pack but what if you want to use different brands and still have the same connectors? The answer is to rewire the packs.
The actual rewiring of packs is not difficult and anyone with basic soldering skills can do it but there is snag, where do you get the connectors? Some places sell extra pigtail connectors like the ones they use but most of the time you have to find other sources. For example you can easily buy JST-XH pigtailed connectors off eBay.
Modifying the connector
There are a couple of cases where a simple modification will allow a connector, or at least the wires and pins, to be used on a different type of balancer plug. I know of 2 of these so far, Hyperion -> JST-XH and Cellpro -> TP.
Hyperion battery -> JST-XH balancer
As it turns out moth Hyperion and JST-Xh use the sam basic plug. They are both .1in spacing and have the same footprint. The only real difference is that the Hyperion plug has a catch for the connector clip. So a Hyperion connector will plug right into a JST-XH plug but we know they are not all wired the same. If you are using a 4s, 5s or 6s Hyperion pack then the connector and wiring is 100% compatible with any JST-XH balancer. If you are using a 2s or 3s pack then some modification is needed in the form of shifting some pins around so they are in the correct places. Here is a diagram that shows what needs done.
This can be reversed but I very much doubt you would ever want to because JST-XH is so common, much more so than Hyperion.
Cellpro <-> TP
Both of these connectors use the same pins but the housings are different. So if you have the housing for the other type, you can take the pins out one at a time and put them into the other connector. Of course you will need to know the correct order for the pins but that should be easy enough to figure out.
Most people that have mismatched balance connector/plug issues will just buy an adapter and that is just fine. The adapter may be in the form of a generic balance adapter board for their charger or it may be a specific single use adapter. Both will work fine and some even offer other, more advanced wiring options. But what if would rather make your own? This is totally fine if you have the correct connectors but finding the correct connectors can be challenging.
Of course the bonus with making your own is that you can make whatever you want. Maybe you want a short balance lead? Or maybe a long balance lead? Or how about a parallel charging lead? Anything is possible given you have the parts and know how.
Just because your battery comes with a certain balance connector does not mean you are married to that type. There are always ways to adapt a battery to a charger whether you change the connector out for another type, make an adapter or even rewire the one that is on there. Find out what works best for you and make it work.