Seems like a few questions have come up about this lately, as LiPo's get more popular and chargers get more powerful i guess this is only going to become a more regular question.
I took pretty much every thing i've learned about parallel charging from the post listed below.
I have asked and been given the permission of the original author to repost it in this forum.
The link to the original thread is included below though and it's well worth wading through the original thread as pretty much everything about LiPo charging is covered there.
So here is Julian's post:
Hi!
I did notice that some people do not know about the advantages of charging multiple packs at the same time on only one charger, wired in parallel.
Instead, many even bother with charging in series.
Therefore, I want to make this thread.
Attention: Do not charge Nixx packs in parallel!
When does charging in parallel makes sense?
-When I have multiple packs with the same cell count.
-When I want to charge them at the same time, thus reducing overall charge time, or avoiding the hassle of starting multiple charging processes.
-When the packs have slightly different states of charge (<30%, to be safe).
-When the charger can provide the current needed for parallel charging, but not the voltage needed for series charging.
What are the advantages of parallel charging?
-No need to care about different capacities or slightly different states of charge.
-Reduced balancing times.
-Simple wiring, fits for a multitude of packs.
When does charging in series make sense?
-When I have multiple packs of the same capacity constantly wired together in series, making a bigger pack
-When the pack's state of charge is nearly identical.
-When the charger can provide the voltage needed for series charging, but not the current needed for parallel charging.
How do I wire packs in parallel?
That is very simple: Just connect every contact of one pack with the corresponding contact of the next pack.
The positive contact is connected to the positive contact, the negative contact is connected to the negative contact.
Simple, isn't it?
And the balancing contacts?
The first balancing contact is connected to the first balancing contact, the second balancing contact is connected to the second balancing contact, and so on.
One can see, that this adapter board has enough contacts to also work with 6s packs. So one board fits all pack cell counts from 1-6s. No need to build different adapters for different packs.
The board in red shrink wrap is a little difficult to solder, but there is a simple alternative:
One can easily see how the contacts are connected.
The pin row headers take the balancing plugs of the packs, and the female header takes the balancing cable coming from the charger or balancer.
Here in another nice image how it can be done:
http://www.rcgroups.....postcount=1895
One can see clearly which contact goes where.
This is another neat example:
http://www.rcgroups.....9#post10883849
Note: Long cables mean no harm, but they can in some cases mean a longer charging and balancing time.
Here one can see a harness in detail:
http://www.rcgroups.....&postcount=274
Another neat example, using real balance plugs instead of row headers:
http://www.rcgroups.....&postcount=122
http://www.rcgroups.....mentid=2254168
http://www.rcgroups.....5#post11255155
Dieter from
KD-Modelltechnik presented the neatest solution I have seen so far in a german forum. The PCBs are not for sale, though. The images should be self-explanatory:
But this is not all: When one only charges with small currents <2A, it is not even necessary to connect the packs' main leads. The balancing cables can cope with this current, so just one pack's main lead has to be connected to the charger.
I have charged up to 5 slowflyer packs 2s 900mAh this way.
One can even use the provided standard adapter for parallel charging. It must only be ensured, that the contacts of all balance ports are connected in parallel. Better check with a multimeter first.
It is very convenient: Just connect all packs at once, and start charging. No need to bother with starting 5 separate charges.
One can see, that just one pack is connected to the actual charge cable. The charge current spreads out to all other packs via the balancing cables.
Here is a very neat setup from Mark:
http://www.rcgroups.....50&postcount=5
He can charge 11 packs at a time.
Note how he connected the main leads to the outer balancing contacts.
This is a very good solution, provided one always charges packs with the same cell number on a given adapter/harness.
If you want to charge with more current, wire the packs like this:
http://www.rcgroups.....7#post10909267
How is the charge current calculated?
Simply add the currents of the single packs.
Say, one wants to charge a 1Ah, a 2Ah, and a 3Ah pack together, each with 1C.
1A+2A+3A=6A.
So these packs are charged with 6A.
There may, however, be the issue, that the packs connected in parallel have a different inner resistance (IR). The older a pack, the higher the IR. This means, that such a pack will not accept the charge current as willingly as a brand-new pack with a very low IR.
Now in the hypothetical situation that one has a lazy old 5000mAh pack connected in parallel with a brand spanking new 500mAh pack, and decides to charge at 1C with 5.5Ah, the chances are good that the small pack will see more than its share of 500mA.
My advice is this:
Know your packs and their health. If you are pushing for the maximum rated charge current of the packs, be sure to connect only those in parallel that are not way off concerning age, capacity, and general health.
If you, however, slowly charge with a small current over night, I do not see a problem.
More on this subject.
Generally, when one has the time, I advise to charge LiPos as slow as possible. Let's say, you want to charge your lipos over night. In this case, there is no need to charge than at 1C or even 2C.
If you have 12h time, use it. Set the current to 1/10C.
I do this all the time. Less current means less problems, less thermal stress for the chargers and power supplys, less risk of anything malfunctioning.
Questions that might arise:
- How come this works with packs of different capacities?
This is because they are connected in parallel. This way, they will always have the same voltage. It is not possible to overcharge a single pack.
Although all pipes have different shapes and volumes, they are always filled to the same level. The same applies to the packs' voltage levels.
- What happens if I connect packs with different states of charge?
A current will flow between the packs. However, this current is not very high, even if one pack is full and the other depleted. Yet, it should be avoided to connect packs with a state of charge differing over 50%
Here is a site that explains everything in a nutshell with great diagrams:
http://sites.google.....allel-charging
Please note: A troll named "cstratton" frequently claims in this thread, that parallel charging is dangerous.
Although he has no data to back up his claims, he does neither accept the data collected by users, which suggest parallel charging is perfectly safe, nor numerous experiences by credible users, which suggest the same.
It is up to the reader to decide whom to believe.
Thanks to Julian for his permission to repost and if you found the post useful please visit the original thread and say thanks.
http://www.rcgroups....hlight=parallel
Cheers
Mark
5
Garry, on 20 August 2008 - 10:45 AM, said:
