LiPo batteries, parallel charged?

I have been searching without luck, in the thread about "Poly vs glow"
first posted on Dec. 6, for the statement on one site presented by a
poster, on "Understanding LiPos". It said in part that "LiPo cells can
be hooked up, charged and discharged in parallel with no detrimental
effect".
Does this mean, if I hooked up 2 packs of 3 cells in parallel, that is
3 series, 2 parallel, I could charge the 2 packs at the same time? Or
for that matter, could I charge 3 series, 3 parallel?
The packs I'm talking about are Thunder Power, 3 celled rated at 11.1
V and 2100 mAh.
Any input would be appreciated,
Wan
Reply to
Wan
Loading thread data ...
The answer is a cuatious yes. Cautious because any charger that relies on the final voltage of the pack to sense when to stop charging will be unable to get things perfectly right if the pack cells are not all in balance.
Parallel cells tend to self balance, but if one goes seriously flat to the point where - say - it loses capacity permamently, then you may get to a stage where it or its mate can over charge, which is violent instant death for the cell.
To be honset, that goes for serial packs as well. Unlike Nicads where the delta peak tends to help pack balancing, it doesn't happen that way on LIPOS. If one pack takes a lot longer to come up to voltage in a chain, others are getting overvoltaged...
I am not sure of teh best procdure for re-balancing packs, but possibly a 0.1c charge - 10 hour rate would do teh trick, or discharge all cells to a common voltage.
Those are the caveats: From what I can glean of E-zone if you don't flatten multi-cell packs too far then what you want to do is what everybody else is doing. Just occasionally tho there is a pop, some smoke, and a nasty fire. Mostly associated with packs that are fast charging after pretty heavy use.
Reply to
The Natural Philosopher
: I am not sure of teh best procdure for re-balancing packs, but possibly : a 0.1c charge - 10 hour rate would do teh trick, or discharge all cells : to a common voltage.
The safest way to balance a lithium pack is to charge each cell individually to full capacity. Thus it is a bood practice when assemling a pack make it possible to (electrically) reach cell for measurement and charging. Some guys in Finland flying big planes with big packs do this by having each cell their own connector, that can then be connected in series with other cells (or taken apart for individual charge).
Charging multiple cell individually takes of course some time, but when one pack is good for 40+ minutes airtime, that can be done at home. Besides, balancing may not be needed but for every 10th or 20th charge...
-Tapio-
Reply to
tapio.linkosalo
My batterie packs are sealed with shrink wrap so I have no access to an indidual cell. Actually the reason I want to charge in parallel is to save time, but not at the expense of safety. Perhaps I should charge the packs one at a time.
These are my first LiPo batteries. How long does it take to charge a pack such as mine?
Wan
Reply to
Wan
: My batterie packs are sealed with shrink wrap so I have no access to : an indidual cell. Actually the reason I want to charge in parallel is : to save time, but not at the expense of safety. Perhaps I should : charge the packs one at a time.
It might also be a good idea to locate the connecting tabs between cells, and regularly measure the voltage of each individual cell. These should be the same, if not, be prepared for trouble...
: These are my first LiPo batteries. How long does it take to charge a : pack such as mine?
With proper current (1C) the charge tome from empty is about 1,5 hours.
-Tapio-
Reply to
tapio.linkosalo
: I am not sure of teh best procdure for re-balancing packs, but possibly : a 0.1c charge - 10 hour rate would do teh trick, or discharge all cells : to a common voltage.
Having slept over this, I realize that indeed that slow charging does NOT work. There is no mechanism in Lipoly that would stop the increase of cell voltage when the cell is "full" as there is in Nickel based chemistry, thus charging even slowly will eventually take the fullest cell over the top... The only way to balance a pack is to charge (or discharge) each cell individually to same voltage.
Ready made packs are usually made of cells from same patch, and these should have the same capacity, thus risk of unbalancing is reduced. But still, t would be better at least to check a pack for balance every now and then (like every 3rd to 10th charge cycle).
-Tapio-
Reply to
tapio.linkosalo
Always charge at one hour rate or less. If you don't flatten em (the secret of happiness with LIPO) about 20-45 minutes realistically.
Reply to
The Natural Philosopher
If empty, then they are dead. Never ever run em to empty. Realistically you probably only can ever use about 90% of the rated capacity safely.
Reply to
The Natural Philosopher

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.