Cell Break In and
for NiMH and NiCad packs
in a nutshell.
What exactly is the balance charge you are talking
about and how do I do it? Is it the charge/10
rate for 16 hours that the digipulse will do? By
the way, thanks very much for going out of your way and finding that
information, I really appreciate it. Thanks
again for the help and take
cells have a daily self discharge rate. Each individual
cell will have a slightly different rate. Generally for
NiCads this is .5% per day, for NiMH cells its 1% per day. Note,
as the cells age this rate tends to increase so it changes over time.
This is one of the big reasons it becomes too risky to use TX
and RX packs beyond the 3rd year. Be aware
also that these rates are only approximate; they will be slightly
different for each individual cell in your pack. The
cells in a new pack will be some weeks or a few months out from the
manufacturer. (With some suppliers they can be over a
year old! Yikes!) So, they've in a sense, been in storage
and had time to change levels from each other. Also, a
pack you own that has been in storage (model last flew last season or
few months ago for example) will have a different level of charge in
When you charge it,
fill up before others. When charging at 1/10th
Capacity, (C/10) (100mah in the case of a 1000mah pack/cell) the cells
that fill up first won't be damaged while the remaining cells are
filled. Also bear in mind you need to put in
about 140% of an empty
cell’s capacity to fill it up. There is some
losses during slow charging. So it takes
total (100mah charge rate x 14 hours) output to fill up a 1000mah hole
a battery pack.
un-balance condition, lets use our example 4 cell pack, think of 4 tall
drinking glasses all side by side in a row. The
first glass is 1/2 full, the second one is 1/3 full, the 3rd one is 1/8
full, the 4th one is 3/4 full. We start to drip
water into the glasses at an equal rate of one drop every 5 seconds
into each glass. The 4th one fills up first,
then a little later the 1st one fills, then the 2nd one, then the 3rd
cell fills. The pack of glasses are now all full. However, the 4th cell was 3/4 full at the start of
the charge (water dripping in the glass) so it was overflowing for a
long time while the charger one by one topped off the other 3 cells. If our rate of charge (speed of the dripping water)
is faster than 10% of the capacity of the cell then damage will occur
on the first cell to fill. It will be
overfilling faster than it can accept, this causes it to overheat
internally and contributes to gassing. So, in
effect, we’ve done damage to our “best” cell.
cell can take
overcharge rate of 100mah without a problem. It
warm up when full but the heat being generated is at a rate the cell
dissipate into the atmosphere. However, if the
charge rate is greater than 100mah (higher than 10% of our 1000mah
a problem is caused. One good way to damage a
is to fast charge an old pack that's been in storage for a long time,
a new pack. It's always best to slow charge
kinds of NiMH and NiCad packs at 10% for 14-16 hours to avoid this
and equalize (or balance) all the cells.
pack that is in regular use gets some overcharge all the time. You can’t know exactly the moment it will become
slow charging. For example: You fly a day,
night, probably some time during the night the pack has refilled it’s
“hole”. It probably Isn’t empty when you put it
in charge unless
you crashed and the battery was dead ;-) . We’ll presume you brought the model home in-tact. When our partially discharged battery fills, the
(wall wart you got with system is presumed or Digipulse or DDVC or
kind of slow charger) doesn’t shut off, it just keeps on charging. A cell that is behind a few Mili-Amps is caught up
during this time.
when fast charging a pack that’s in regular use, there is a little bit
of an overcharge at the end of the charge cycle. (Excepting
Sirius and Ace fast chargers which are peak predictors an go into
trickle to accomplish same effect.) A peak detect charger
is looking for a drop off in voltage to find the “Full Point” of the
pack. It’s voltage is dropping because it’s heating up,
it’s heating up (where you paying attention earlier?) because
it’s full and still under charge.
With all the above
in mind, here is what you do:
Find the capacity of
your battery pack. Lets say it’s 1650mah.
Capacity X .10 to arrive at 10% of this number. The
answer here is 165mah.
charger to charge at 165mah.
back 14 to 16 hours later and the battery is ready to use.
if I can’t set a charge rate of 165mah?
to skin the same cat is to multiply your capacity (1650) by 1.4
This gives us
the 140% we need to put in to fill up a pack. The answer
answer (2310mah) and divide by the output of your charger, answer is
“Hours” to full charge.
If your using
a Digipulse (max setting is 150mah) the answer is 2310/150= 15.4 hours.
your using a 100mah wall wart the answer is 2310/100=23.1 hours.
If your using a 50mah wall wart the answer is 2310/50=46.2 hours.
Warning! If your
answer is less than 14 hours then your charging higher than 10% of
capacity, the pack will be damaged!
That is balance
charging for NiMH and NiCad battery packs in a nutshell.