Yes, that's right about needing dummy cells, I did have a problem with the balance connectors at first, but I managed to fix that by making balance wires interchangeable using screw type connectors. It's a little trouble, but it works.
Is there a reason you can’t connect all the balance harnesses in parallel? You’d still need multiple connectors for either the -ve or +ve power connector of course.
Hmm, I don't really see how it would be able to work in parallel using balance plugs. It would work without using balance plugs, but then again it isn't a good idea to charge in parallel due to differences in internal resistances in each cell. Unless, they have exactly the same internal resistance, one cell will charge at a higher amperage due to this and charge faster while the other will charge slower. It's potentially dangerous because of overcharging.
Charging in series with balance plugs allows cells to charge evenly because the balance plugs will bleed off the extra voltage/current.
You need a bananaplug on every cell to charge all kinds of counts. That’s what I said. Please correct me if you can charge with balance plug onlys.
You can connect all slots with one big balancing connector, this makes no differnts as the 2s balance connector of your charger is the same as the first two cells of the 4s slot(these are electrical conducted)
But then you need the power cable on every battery, this could be done like above just two bananaplugs more, so no big trouble and easy to use.
I am also not sure what happens if you charge uneven discharged batteries, I guess this will stretch the
But the main problem for an universal cradle is the cradle as it has to be 80mm long and 35mm wide or so to fit all kinds of batteries.
If you only build a customs cradle to charge one special battery set very fast and good the above one works perfect, but I would like to have a universal cradle. These exist for normal battery sizes(around 60mm ±) but I haven’t seen some for cylindrical cells.
Yeah the whole point of this exercise for me was to avoid balance charging as I may not be charging the same cells at the same charge. This is why I bought a 4 channel hobby charger. I need to quit being lazy and gut/modify the chargers that Werner recommended. I have 4 of the chargers, it just takes me a while to build up the motivation to do things lol
This is what I meant. 
@photon1k:Oh wow, I'm confused lol. I don't know how the charger would read that, it might give you a voltage error.
@Werner: Hmm, I think your talking about individually charging each cell in each charging bay. My charger mod is wired in series like this:
It can charge batteries as big as the 32650s. I don't normally use protected cells, but if needed the negative contact plate can be trimmed to fit longer cells due to protection circuits.
Heh! It looks unorthodox I admit, but your diagram is the same as my 4S option. It’s just that there are some extra balancing wires in parallel with the 4S wires. If you check your charger you will likely find that the balance ports are wired in parallel. You can use a DMM in continuity mode to verify this.
Edit: To clarify, for example, pin 2 of the 2S port is connected to pin2 on the 3S, 4S, 5S and 6S ports.
Photon that is what I meant too, so you only need one 4s balance plug.
And of course the individual bananaplugs, which you have in your drawing too…
Yes, the drawing shows two, three or four-cell options. It can be constructed to balance charge from 2 to 8 cells. If your max cells = 6 then use a 6S harness plus a negative connector for each cell. If you’re only charging 4 cells that day, plug the -ve power wire into the fourth cell.
Is there a reason not to charge multiples in parallel? Is it just that they all have to start out around the same voltage before charging, vs. charging in series with the balance connector which can deal with cells of a wider range of voltage?
I have enough 18650s that I wait until I have 6-8 that need charging, and sort them into groups with voltages within a range of about .1v, put them in the parallel box and let them equalize for a few minutes, then charge.
Balance charging is a wee bit safer because each cell is monitored by the charger. Balance charging doesn’t stress the cells the way parallel charging does. For the brief moment when cells are first connected for parallel charging, there can be a large rush of current between the cells.
I’ve never really worked through the math, but I’ve read that the current can be high enough to stress the cells. That is why it is recommended to only parallel charge cells/packs that are very similar in voltage. That said, the serious helicopter guys often parallel charge their large 5 and 6 AH LiPo packs. They do it because although it’s a bit harder on the packs, they often have six or more packs and they usually charge them the night before they are flying, so it’s much faster to parallel charge.
I have measured current between two cells of differing voltage when connected in parallel, and even at wider differences (up to .5v difference) than the cells in my groups the current is very small. These are all conventional non-low-internal-resistance cells though, other cells might behave differently.
Ah! That’s why a couple of my cells behave that way!
I think it’s more of a concern when parallel charging packs of differing capacities. The equalizing event also happens when cells are loaded into a parallel light too. And it happens pretty quickly so I imagine measuring it would not be easy. How did you accomplish it? I would like to try.
Easy, just connect the negative poles together (stand them on a metal plate), and connect ammeter between the positive poles. Creates the same circuit as when they're placed into a parallel holder, except you can measure current flowing from the higher voltage cell into the lower voltage cell.
I was just reading a little more about this on rcgroups.com and the concern seems to be about the larger packs with high C ratings. Although it can take minutes for the packs to fully equalize, the large inrush current occurs in the first few seconds. There were deliberately large voltage differences between these two packs and they were fused to limit the current. I don’t know how applicable any of this is to our small cells given the IR/C rating and capacity differences between them and these LiPo packs, but the current is impressive.
I'm not claiming the stronger cell won't charge the weaker cell, or that it's impossible to connect any two cells in parallel and it be safe. I'm only saying with single cylindrical cells we use in flashlights, as long as the voltage is close, the current flow between cells will be relatively small. Measure it, don't go looking for examples that aren't relevant to what we're discussing here.
Two identical Panasonic NCR 2900s, one at 3.99v other at 4.19v. Peak current between the positive poles is .76A and falls steadily. That's a much wider spread than I would ever use when charging multiples in parallel. I also never mix different cells - only charge the grey Panasonic 2900s with other grey Panasonic 2900s, purple 2800 Samsungs with other purple 2800 Samsungs, blue no-name 2400 Chinese cells with other blue no-name 2400 Chinese cells... I'm pretty sure trying to charge a totally flat 16340 and a nearly full KK 26650 in a parallel rig would lead to some pretty not-nice things happening. So don't do that.
Just to clarify, I assume this is correct only if the charger is powerful enough to double (or triple, or quadruple) the charge rate?
For example, charging 4 cells in parallel if the max charge rate is 6 amps (as in Accucell 6, Imax B6 etc) will be slower than balance charging them at 3 amps.
Parallel seems like lots of maybe issues, not so in serial, my rule only bang head on soft and/or smooth surfaces.
Deal killer could be parallel exceeding current limit of charger long before voltage limit in serial connection.