Bilding a 'distributed' 3s 6p Li-Ion pack

Hi to you all.

I am into design (and later and build) my own hexacopter, that will be powered by a 3s Li-Ion pack.

I want to hide the batteries into the frame components, which could be done in the rotor arms.
Each arm can hold at least one 3s pack, (may be even 2). Let' s start with one, for the discussion

Of course I want to balance the cells while charging.

When I google for a 3s charger, I find balanced chargers that have 2 connectors, one for the charge wires and one for balance wires, I guess. Am I correct that the designated 3s pack will have balance wires in it, but no BMS ? As the BMS is in the charger ? (On my e-bike, the BMS is in the pack itself, not in the charger)

This brings me to question 1: Is balancing a ' charge' thing, or also a ' de-charge' thing ?

If not, I will build 6 packs and charge them, balanced, individually. (May be with 6 parallel balanced 3s chargers in a diy power station)

Than, I will wire/connect all charged packs in parallel to a power hub I want to build in the copter.
This will render the set virtually as a 3s6p.
From the power hub I will power the hexacopter.

Is this a viable concept ? Or do I miss some essential Li-Ion technology demand ?

Please surprise me

Rgrds Thomas

Best to parallel first, then serial connect.

Each parallel Group is treated as a single cell, cells within will self balance.

When match-testing capacity, end up with each group as even as possible.

Serial connections between Groups should have +/- same length / gauge / resistance.

Balancing can be via charger or BMS at the top, or if bottom balancing, dedicated balancer device ("non-protective BMS") and obviously not while charging but using a discharge circuit.

However you do it, all at once, not separate packs.

A protective BMS is separate from the charger, many do without.

If desired, a LVC cutoff will suffice, best tied to lowest Group voltage.

Parallel first is not an option.
It will be 6 separate packs of 3 cells in series.

so they will only be parallel when connecting them to the power hub.
I hope they will balance themselves at that point. The individual packs will have all 3 cells balanced by the 3s charger.

Once you connect the batteries to the hub, they will stay in balance as long as all the balance connectors are connected together. When that happens the voltage equalizes.

Is this parallel balance board something you will be using as a hub. All the batteries will equalize in this manner while charging or discharging.

Balancing only happen while charging, the charger will balance the packs when nearly full, it will bleed the high cells and let the other cells catch up.

I have never seen that balance hub. May be it is something I need.
But it shows only power leads. How can it balance the cells in the individual packs ? Or is that not necessary ? I can imagine it balances the packs. this hub would be a great add-on for my design, if the individual packs benefit from it too...

Can you share a link to it ?
tanks Thomas

ThomasEekels said:

Parallel first is not an option

Click to expand...

Why not?

You will definitely see imbalance issues between the modules going that way, even with active balancing gear at that level,

resulting in reduced performance and shorter lifespan.

jonyjoe303 said:

Balancing only happen while charging, the charger will balance the packs when nearly full, it will bleed the high cells and let the other cells catch up.

Click to expand...

That is only true for a particular style of balancing circuits.

Yes the most common style, but there are many devices that do it differently, and in many use cases much more effectively.

And then there's bottom balancing, middle balancing, manual-only balancing. . .

ThomasEekels said:

I have never seen that balance hub.

Click to expand...

The idea is each #1 cell in every pack is paralleled, also #2 and #3. So each of those triplets self-balance within the set.

That has nothing to do with balancing between those sets connected in series, usually done with the charger, or BMS, but can also be a separate dedicated balancing device.

https://www.rcgroups.com/forums/showthread.php?1139916-Charge-Multiple-Lipolys-At-The-Same-Time-On-A-Single-Charger

Years ago, LiPo from the RC world was the easiest option for a high-amp pack. Plenty of ebikes were built with no BMS on the bike.

All the lipo packs were balanced by the RC charger. Many of the packs were bulk-charged by seriesed Meanwells several times before the owner would do a balance charge. (*ride and bulk-charge every day, balance-charge once a week?)

For charging all the sub-packs in parallel from one charger. Ideally individually fused, otherwise need to ensure only doing this with healthy packs.

Reliable supplier, many styles.

https://www.progressiverc.com/charging/charge-boards

https://www.google.com/search?q=site%3Aprogressiverc.com+Self-resetting+polyfuses