I wrote this page to give you an idea of what parallel LiPo charging is and the reasons it is so popular so you can decide if it's a charging method you may want to use, (now or later); and why getting a higher power RC Battery Charger and RC Power Supply might be a good idea in the long haul even if you are only using smaller capacity LiPo Battery packs right now.
At the bottom of the page I have included several links to the actual parts I used when building my parallel charging harnesses if you decide this is a charging method that is right for you and need an inexpensive parts source. If you would rather just purchase "ready built" parallel charging harnesses & boards, Buddy RC has a great & growing selection and very good pricing - click here to check them out.
I have started using these ParaBoards while "Para Charging" and they are the best solution yet in my opinion. They make for a neat, hassle free hookup and they are pretty much "goof proof". Highly recommended if you parallel charge and don't want to build your own harness &/or boards. I have 6 of them now and they rival pizza on the "can't live without scale" as far as I'm concerned ;-)
Anyways, enough with the pizza promotion, let's get back to the topic at hand - Parallel Charging or "Para Charging" for short...
Parallel LiPo charging allows you to charge more than one battery at the same time with your computerized RC battery charger. The big advantage of parallel LiPo charging is it saves time since you can charge your entire heard of LiPo batts on one charge cycle and is considered by most to be safer than serial charging (one pack at a time).
Parallel charging will only work on same cell count batteries, but they can have different capacities (within reason). They can also be at different states of discharge - again within reason. You wouldn't want to try and parallel charge a pack that was 5% discharged with one that was 80% discharged for example.
The general rule I follow is no more than a 0.1 volt maximum difference between cells of packs I hook together in parallel. This for example would be very close to the voltage difference between a cell that is 80% discharged (around 3.75V) and a cell that is in a 50% storage state (about 3.85V). The larger the voltage difference between packs hooked together in parallel, the larger the amount of current that flows between packs as they all equalize.
At any rate, no more taking one pack off when it is finished and then hooking the next one up and starting the charge cycle all over again. The important thing to remember is the battery packs all have to be the same cell count. You can’t parallel charge a 6S pack with a 4S pack for example - all packs in the parallel charge circuit must be of the same voltage rating.
Words Of Caution!
Parallel LiPo charging is an advanced method of charging and requires a certain level of electrical understanding. If you are not comfortable with charging calculations, wire sizing, your ability to build safe parallel charging and balancing boards/harnesses, or keep your wits about you when hooking up the batteries in parallel, please don’t attempt it.
As was discussed on the LiPo battery page , lithium battery chemistry is a volatile mixture. One battery starting on fire because of unsafe/improper charging is bad enough, never mind several batteries all hooked up in close proximity to each other! If you choose to charge this way, just like charging any lithium based battery, you do so at your own risk and never unattended.
If you understand how Ohm's law works in relation to parallel circuits, you know the basic principle behind parallel charging, how it works, and why it's just as healthy for the LiPo as single pack charging - perhaps even healthier. I have experienced this almost every time I parallel charge... The voltages of the individual cell branch circuits are almost always in closer balance proximity during the charge cycle and the charger doesn't have to work as hard putting a load on a certain branch to bring it/them down to balance with the rest of the cells/branches in the pack.
Why... Simple law of averages. The more packs you have hooked up in parallel, the more evened out the internal resistance values will be between each branch of cells since it is very unlikely cell # 3 in all your packs has a slightly higher internal resistance than cell # 2. The more common reality is every cell in every pack will have a marginally different internal resistance and this will even the resistance out on each cell branch very nicely resulting in the voltages between branches being very even as well while the packs all charge. Again, just simple parallel circuit Ohm's law that we all learned back in high school physics - assuming you weren't skipping class that day.
First you will need to build or purchase a parallel charge plug or board that the charge leads from each battery will be plugged into. The positive from each plug is hooked to positive and the negative of each plug is hooked to negative (parallel circuit). To keep things in reason, most will only build a plug or board that will support up to 5 or 6 batts maximum.
Things start to become a little congested as you can see with that amount of wiring and batteries, especially if you still want to use a fire safe charge container or bag.
The picture above is showing a parallel charge board I built that supports all my LiPo packs that have Deans connectors. As you can see on the back side of the board, all the plugs are wired and soldered in parallel.
The reason I built a board over a multi plug harness is so the male ends of the Deans plugs can’t short against each other (one thing I really don't like with Deans connectors).
After you build your board, make sure you insulate the back side of it. I for example just used several layers of fabric hockey tape.
Here is the EC3 connector parallel charge plug I built and since EC3 connectors are insulated (better safer plug in my opinion), I didn’t bother using a board and just wired them all up in parallel.
One thing I should point out is the size of the wiring, especially the main wire from the banana plugs (red/black) to the connection point of the 5 EC3 plugs.
I could theoretically be pushing 20 amps through this wire so it has to be a fairly good size gauge. I am using 14AWG and this seems very adequate. It only gets a little warm at a full 20 amp current load and the voltage drop over the very short length of wire is insignificant. 14AWG is also the size of the wiring used to power my charger, so that is a pretty good way to "gauge" it :-)
Hear's another example of a parallel charging harness I built that supports all my smaller LiPo packs that use JST connectors.
Next you will need to build yourself a parallel balancing board or harness. I am first going to show the board I built and then a harness. Again, just as with the charge plugs, you generally need no more than 5 or 6 balance plugs to keep things in reason. As the name suggests, this board is also wired in parallel as you can see in the above photo.
The board I built here uses 6S JST-XH balance plugs since most of my LiPo packs use JST-XH balance taps and JST-XH plugs have a nice advantage... you can (with a little persuasion) fit different plug counts into the plugs.
For example, a 3 pin balancing plug will still plug into a 7 pin plug. This is nice so you don’t have to build several balancing boards with different plug pin counts.
I also have a few FlightPower and ThunderPower packs that use Thunder Power Taps, so needed to get a few TP to JST converter plugs.
Just like the parallel charge board, ensure you insulate the back side of the parallel balance board so it won’t short out on anything.
The parallel balance board you built will now plug into the Chargers balance board.
Here I have my parallel LiPo charging balance board plugged into the 6S plug on the balance board that came with the charger enabling me to parallel balance everything from a 2S pack to 6S pack. If I ever get into 7S, 8S or higher, I will have to build a new parallel balance board, but for now, I am very content with nothing larger than 6S packs.
Here is another parallel LiPo charging balance method that will work and I find easier to both build and hook up. With a balance harness like this over a board, it is easier to hook up all your balance taps, especially if your batteries have short balance leads.
The first step is to get a number of female balance plugs with wiring on them if possible. Having the wiring in place saves considerable time. The 6S JST-XH ones I am using here came with Kokam male ends (they are actually a balance adapter) but they come in packs of 5 for less than I could get single ends for anywhere.
I just cut the Kokam ends off and went to work soldering all the leads off the 6S JST-XH female plugs in parallel. Mounting them all lined up in the correct +/- orientation in a small vise as I have done here while working on each branch of wiring keeps things neat and mistake free. Also note I have heat shrink already in place for insulating the solder connections when I put the male balance plug on.
Once I have all the wiring sorted and soldered it is time to solder on the single male balance plug end that will plug into my chargers parallel charge board. As it turned out, all those Kokam male ends came in useful for this.
I just shaved the orientation tabs on the sides off the Kokam plug and swap the black and red wires so the polarity was correct. Now I have a 6S JST-XH parallel balance harness that plugs directly into my 208B charger's balance port making the hookup a little neater.
This is perhaps the question I get asked most often "what charge current do I use when parallel LiPo charging"? It's really simple math here. Basically when you have everything hooked up in parallel like this, your individual packs now have become one single big capacity pack.
I'll say that one more time in case you missed it. YOUR INDIVIDUAL PACKS HAVE NOW BECOME ONE BIG SINGLE PACK! For instance, if you hooked three 2200 mAh 3S packs all up in parallel as I have done here, they essentially become one big 6600 mAh 3S3P pack.
As per charge current calculations, a 1C charge rate on this pack is now 6600 mA (6.6 amps). A 2C rate would be 13.2 amps, and so on. I think you can now appreciate why high power chargers are generally required with this parallel LiPo battery charging method, as the wattage required in this example will be in the 83 Watt range at 1C and about 166 Watts at 2C.
Of course you don’t have to charge at a 1C or 2C rate, lower charge rates are always safest so a 0.5C rate of 3.3 amps (41 watts) will work just as good, it will just take twice to 4 times as long to charge.
The same calculations apply to packs of different capacities. Let's say we have one 4S 1500 mAh pack, one 4S 2800 mAh pack, and one 4S 4000 mAh pack all hooked together in parallel. That is the exact same thing as far as the charger is concerned as a single 4S 8300 mAh pack. A 1C charge rate set on your charger would therefore be 8.3 Amps. Again, just simple math :-)
Connection Warning Tip!
One very important caution when you hook all your packs up in parallel is, you MUST plug the main power plugs from the packs into the para-harness, or para-board first.
This way the potentially large current flowing between the packs as the voltages all equalize when they are first connected all together flows through the heavy power wires and connectors without issue. If you were to plug the balance plugs in first, that same potentially high short term voltage equalizing current flowing through the small balance wiring could overheat those small gauge wires, or the small balance plugs. It could even melt the circuit board trace lines on the Para-Boards. If all the LiPo packs are at the exact same voltage potential when you hook them together in parallel, this is not a concern as there will be little to no current flow between all the packs because they are all at the same voltage potential. In the real everyday world however, that is likely not to be the case so it's always best to plug the main power plugs in first and then the balance plugs.
Hopefully that gives you a little background and understanding on parallel LiPo charging and several methods of how to do it. As I said in the opening paragraph, the main reason I built this page was to show you why a higher power charger, even with smaller battery packs, may be a good long term investment.
You'll know you're a Parallel LiPo Charging junkie when...
Here's a good video of LiPo parallel charging procedure...