So, You either are currently using LiPo
(Lithium Polymer) or are planning to use them with your RC aircraft/car?
there are some important things that you need to know about using and
charging these types of batteries. Lets go over the basics of safety
you REALLY NEED TO KNOW!
ONLY use a balance charger designed for LiPo batteries. Charging a LiPo
with another type of charger WILL CAUSE A FIRE.
discharging (charging to 5% or less capacity) will damage the LiPo and
likely make it PUFF and/or not perform well for subsequent flights/uses.
3) A properly fully charged LiPo will be 4.20V per cell.
Operating a LiPo to 3.0V or less under load (no
matter what the capacity) can damage the battery.
Puncturing the outer foil casing around the battery cell renders the
battery into an unusable and often dangerous condition that can cause
smoke, heat and/or fire.
Operating a LiPo above 160F will damage the battery. If it's too hot to
touch and hold onto, that's about 140F and likely, your over taxing the
6) Lipos don't perform as well when too cold or too hot.
Room temperature is a about a good average temperature where Lipos
Lipos will last longer if you store then at storage voltage (about
3.85V per cell) and at a cool temperature (NOT in the hot car or
garage). The longer you plan to let them sit, the more you should be
putting them in storage voltage and putting them some place cool like
8) LiPos deliver more power when warm but not hot.
Cold weather will Increase Batter Internal resistance and make
them not deliver as much power. Keep them in the car when flying in the
are a number of procedures people follow. If the manufacturer has a
procedure that is recommended, you should do that. But here
what I do (Assuming a 6-8 minute calculated run time):
Start with a complete Balance Charge (Lipos are typically shipped half
charged [storage voltage])
Flight #1) 2 minute at 1/2 throttle (for a helicopter, simple hover),
Then Balance Charge.
Flight #2-4) 2 minute at 1/2 throttle, Stop for 2 minutes, 2 minute at
half throttle, Then Balance Charge
Flight #5-#8) I take it easy, not hard flying and target discharging
Setting the Timer for
your timer so you do not exceed 80% discharge. No better way to degrade
a battery than to overdischarge. If you set your timer for
discharge, then you know you have enough time to deal with special
circumstances after the timer goes off. Start slowly and keep
increasing your timer until your flying and you know how long say 75%
discharged is. If you hit the timer and you've been taking it
easy, maybe fly longer, if not, land when the timer goes off.
a Helicopter, I set the timer about 1.5 minutes less than how long I
can hover and get an 80% discharge. How long your battery lasts depends
on how hard your working the throttle. (same goes for Helicopters, more
3D and hard flying, the less the battery lasts). A timer will work if
your flying is consistant and you are monitoring how much mAh your
putting back into your battery. A hard flight? End it early.
Taking it easy? Maybe consider adding a minute to your flight?
you can connect batteries in Series and run them. Many people do this.
You want to buy or make a series harness so you can keep and
charge the batteries individually. I recommend (and many
people do) that when you run 2 batteries in series, that they be the
same brand, C rating and Capacity and age/use. They don't need to be
the same size though. For example, I often run 2 3S 2200mAh 20C packs
in series in a combat plane to make a 20C 6S 2200mAh pack.
can also run say a 2S 2200mAh 20C in series with a 3S 2200mAh 20C pack
to make a 5S 2200 20C pack. Some people do this because 2 and
Cell packs are easier to acquire. Or they do it because for
case, I have LOTS of 3S pairs hanging around from Helicopters and I
sized an Airplane motor to work on 6S 2200. If you DON"T make
sure the capacity and C ratings match, what can happen is one battery
pack may drop more voltage under load (See Internal resistance below).
This may not be seen by your ESC battery monitor, but that pack may end
up puffing or discharge more than the other pack. If you have
access to a charger that can measure Internal resistance, it would be a
good idea to matcht he batteries to similar IR values (withn 30% of
each other). The shorter the runtime of the aircraft and the harder you
are going to push the battery, the more critical this becomes.
(Read section on Parallel charging).
can connect batteries of the same Cell count in parallel and run them.
When connecting in parallel, you can get away with different
capacities and C ratings. You don't want to get too carried
with the difference but what will happen is that most of the power will
come from the higher C rated pack (or the higher capacity pack) and
less from the lower C rated (or lower capacity pack). Some cross
charging will occur when the motor is not running but in general will
be fine. Connecting in parallel is less common but some
it when they don't have a large enough capacity pack. 2 3S
2200mAh 20C packs in parallel make a 3S 4400mAh 20C pack. In general,
it's best if the larger capacity pack has the higher C rating. Before
parallel connecting packs, you should seek advice from a forum to see
if what your doing is ok. Paralleling a 3S 2200mAh 20C pack
a 3S 500mAh 30C pack may not be the best idea.
can charge batteries in Parallel. You should always do this with a
parallel Charge harness and a Parallel balance harness. DO NOT charge
without all batteries connected with the balance leads in parallel. Example
of a 3S JST-XSH balance port parallel harness.
It will be best if the batteries are in a similar discharge
but not an abolute requirement. Once again, read up on this
subject before commensing (RCGROUP thread is a good resource).
often will run 2 batteries in a plane in series, but then charge in
parallel. One down side is it's much harder to see a degraded
pack after/during a parallel charge. It's advisable to individually
balance charge them once and a while to see the health of the pack or
to keep track of the pack's Internal resistance value if your charger
can measure it.
Charging in Series
you can do this, I don't recommend it. If you have 2 discharged packs
that are not identically discharged, the overall time it takes to
charge will be much longer. Especially the balancing phase.
pack will achieve CV (constant voltage) mode before the other, the
charger will reduce current and the 2nd pack will take much longer to
finish charging. 2 3S 2200mAh packs for example that might
an hour to charge in parallel could end up taking HOURS to charge in
series if you did not discharge them the same. For this
most people will parallel charge packs.
of the most underdiscussed and actually very importan aspect of a
battery is Internal Resistance. All battery cells have an
internal resistance that has an important effect on performance.
Following Ohms law (V=IxR), there is a voltage drop in
output where the voltage drop is proportional to the Current the
Battery is putting out (I) and the Resistance internal to the
(We abbreviate that as IR
a battery's Internal Resistance). How you see this realized
when you put a load on a battery (battery delivers current) and the
more current it delivers, the lower the voltage output of a battery.
Yes, Not only does a battery voltage drop as the battery
is used up, but the more current you pull from a battery, the more it
drops the voltage. The lower the IR, the better the pack
(typically measured in milliohms for LiPos). Where does that
in voltage go? Heat is the answer. The pack gets hot. The
the IR, the hotter the pack gets. That means at higher current draw,
energy is wasted and turned into heat. Quite often, when a
bogs under load, it is likely the battery performance than the motor
(if the motor was properly sized). Most of the time, a
from the same manufacturer will have a lower IR per cell the higher the
C rating. Not all manufacturers are rating their packs the
so you can't compare a brand X 25C pack to a Brand Y 25C pack and
expect the IR to be the same. More often then not, they aren't.
You also can not coorelate C rating to an exact measurement
IR. Larger capacity packs of the same C rating typically have
lower IR per cell than smaller capacity packs.
One way to quantify the affect of IR on motor performance is with this
motor calc tool:
Simply change the
resistance per cell value around and see how the motor RPM and Wattage
RC Airplanes, a Lower (Better) IR per cell value will give you MORE
peak thrust/RPM. It will slightly increase your flight time as well as
the needed Throttle you give the plane will be less because more power
is transfered to the motor than given off as heat in the battery.
RC Helicopters, the lower IR battery pack will yeild a higher RPM
(non-governed) during hover and flight. Flight time will
increase but more if you lower your throttle curve to compensate back
to your original RPM when using the weaker pack. You will
notice the total power in the helicopter increase as you give suddend
pitch increases and the "POP" in the helicopter improves (less bogging
at full positive or negative collective).
Many of the newer
chargers (Like the iCharger series) measure Internal Resistance per
cell. You can measure the IR and track the IR during the life
the battery. A faulty cell(s) will often be marked by an increase in
IR. Puff a pack due to drawing too much current, overheating
(poor ventilation) or running the pack down too low and you could see
an increase in IR for one or more cells. This damage in increase of IR
is not recoverable.
is affected by temperature. So the warmer the pack the lower the IR. So
flying in the cold will increase IR (but the pack will warm up in
flight so mostly your initial power is what suffers). If you want to
measure and catalog the IR of your packs, do so at room temperature
70-75F and let the batter stand about an hour after getting a full
charg for consistancy. Measuring the cells of the pack may not
always add up to the value you get when measuring JUST the power plug.
Power plugs and the internal circuit board of the battery add to the
Useful Links to read:
RCGROUPS Battery Guide Thread