Does a 1S4P 18650 battery need balancing? I read a lot about balancing around the internet. To me it seems like this only applies to the cells connected in series. An all parallel setup would not need balancing. Is this correct?
Electronic – Balancing of 18650 battery with parallel cells
balancingbatteries
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What colour is the magic smoke when it vents with flame ? :-)
Rushing immensely, more later, but ...
What you describe seems to run a severe risk of doing damage.
To be ure, first you need to specify the allowed MAX charge rate for each LiPo.
You have 1.0 + 1.2 = 2.2 Ah in parallel so 5A = 5/2.2 = 2.27C.
This MAY be OK if cells are specd as 2C or more and are balanced in draw.
If specd at say 10C then it all may survive.
If specd at 1C it is very very bad.
BUT when a cell pair plateaus at 8.4V it's current will start to drop and if the charger is able to make 5A the extra current WILL flow into the still in current more other battery pair.
If max charge rates are not >> 2C then what you describe is at best an extremely poor compromise and at worst a disaster either in magic smoking or in cell lifetimes.
If max charge rates are around 2C then what you describe is at best a beating of some of the cells regularly and at worst a journey towards magic smokedom.
In an arrangement like this with different capacity pairs wired in parallel you need to carefully monitor individual cell pair or even cell voltages to prevent discharge-damage. This is going to make balancing more important, although I have been impressed with how well cells from the same batch seem to track when I have checked it (not often).
Operating cells of different capacities in parallel is an immednsely bad idea usually unless you manage and turn off each pair individually.
Apart from one pair endpointing before the other and throwing more charge or discharge onto the other there is a lack of certainty re how cells load share.
eg Say you have a 1000 and 1200 mAh cell and load both with 1000 mA. The large cell will see this as less of a percentage load so it's natural terminal voltage will be larger and it will "happily" supply the extra current. but there is no guarantee that it will o this in the ratio of the tywo capacities. The large cell may prove very "sacrificial and provide most of the load for most of its capacity. BUT when it finally falters the small cell will then take up most of the load and may now be overloaded. And there is no certainty that the LARGE cells will not now expire and be driven into a damaging mode. Probably not, but. too many uncertainties.
Why run cells of different sizes and in this 2 x 2 pattern?
Key question: What are the max allowable charge current rates for the 1000 and 1200 mAh cells.
Without this information the question become svery hard to give a good answer to.
Cells in devices that you do not wish to be a flaming ruin MUST have protection.
Having protection circuits does not guarantee it will not happen.
Cells without protection are intended for use by either manufacturers or experts or enthusiasts who add their own or for suckers.
Whole device protection and cell protection are complementary and serve overlapping but different roles.
4,000 mAh 18650 LiIon batteries are ~~~= 99.9% +0.1% - 0.0% sure to be rubbish.
ie not just < 4000 mAh but << 4000 mAh and low quality.
The people who bogus label cells
almost never feel an obligation to use the best cells they can and
almost always decide to add injury to insult by using junk as well as lying.
Real world experience shows that the value of 'almost' is very high in both cases.
Higher capacity cells can usually be fitted OK.
MUCH higher capacity will lead to long CC tails and overcharge but not an issue here as mAh_new is < to << 4000 mAh.
ADDED:
Notice that in this ad and all their other ads they ALWAYS show non-brand-label views of the battery.
However, you may find that the racing stripes and general colour scheme a good match for the well known "Ultrafire" brand batteries. This may in fact be a real brand and these may be real examples of it BUT you can buy empty shrink wrappers to apply to the battery of your choice with this (or other) branding on it , so caveat emptor. Better nullius emptor I'd hazard.
These ones are a stunning 6800 mAh - a steal at the price. Available here
You'll find others similarly arrayed here and
here - 3000 mAh and 4000 mAh and
6800 mAh !!!!!!!!!!!!!!!! {again}
and unspecified but with GENUINE CREE 2000 lumen {so 20+ Watt} flashlight for $9.27 and
only 4000 mAh and
that's better - 4200 mAh
and .............
Flee!
Best Answer
No. In parallel they are electrically a single cell. You can't 'balance' a single cell.
However before connecting the cells together you should make sure that they all have close to the same voltage. If they are new then they should do, but if they are used then you may need to 'balance' them before making the pack.
Don't make a pack from cells of different capacity, type, age, or condition, as they will not share the load equally.