RCU Forums - Battery Question

Electric flyers have an advantage over glow and gas flyers. We don't have to
buy flammable liquids that have to be stored and handled. And there is no
issue around exhaust residue. The planes are quiet and generally neighbor
friendly.

However we do have to know more and invest more in battery chargers and
batteries. For the other guys, the charger that comes with the radio system
may be all they will ever need. For us, these are our fuel tanks and filling
stations.

Let's look at batteries and chargers. I am not going to go into battery
chemistry. Let's just say that you need to use the right charger for the
right battery. Don't mix and match or you could create a dangerous situation.
Used properly they are all safe to use. If you want to know more about NIMH,
NICD and Lithium batteries, these links contain useful information.

Battery Basics:
http://www.modelaircraft.org/mag/FTGU/Part8/index.html
Notes on Lithium Batteries
http://www.*********.org/lithium_bat...eakthrough.htm
safety warning on Lithium Batteries
http://www.modelaircraft.org/safetycom.asp

Transmitter and Receiver Batteries

Just a few words on transmitter and receiver packs. These are typically made
from NICD or NIMH cells that are designed for lighter loads than motor
batteries. As such, they need also to be charged at slower rates. The
general rule is 1/10 C charge rate where C is the rated capacity of the
battery. So, on a 600 mah transmitter or receiver pack would be charged at 60
mah. At this rate you would charge an empty pack for 10 hours to bring it
fully up to charge. This is handled nicely by the charger that comes with the
radio system. This is an example of such a charger. The key is to read the
instructions that came with your radio and follow them.
http://www2.towerhobbies.com/cgi-bin...&I=LXNK66&P=ML

Quick charging these packs is not recommended as a standard practice. However
some people will quick charge them if they run down at the field. Just be
aware that this can lead to a shorter life and can cause pack failure. If you
do quick charge, try to keep it below the 1/2 C level and don't do it too
often. They just don't like it.

If you quick charge them, they will likely get hot. Don't quick charge them
in the plane or the radio as the heat build up could damage some of the
surrounding electronics or might deform plastic or epoxy based components near
them. Fast charging at 1C will generate a lot of heat and can lead to early
pack failure which could happen during a flight.

There are after market chargers that are focused on transmitter and receiver
packs. Here is an example from AccuCycle
http://www2.towerhobbies.com/cgi-bin...&I=LXL357&P=ML

Charge 'em slow and treat them right and they should last for years. If you
tend to fly for long periods, pick up an extra transmitter and/or receiver
pack and charge them slowly, at home. Then, you can just swap packs at the
field. That is what I do. Most radio makers offer extra packs and there are
a
number of third parties that make them. Here are a couple of examples.
http://www2.towerhobbies.com/cgi-bin...ry&FVPROFIL=++
http://www.amondotech.com/index.asp?...S&Category=228

Nuff on transmitter and receiver packs

Motor Packs

The motor on the typical parkflyer needs to pull power at a much higher rate
than a receiver pack can provide. So the batteries that power the motors are
typically of a different design/grade so that they can supply electricity
at these rates. As a result when we charge them we can charge them much
faster too.

The general rule here is that NICD motor packs can be charged in the 1.5 - 3C
range with 2C typical. NIMH packs are best charged at 1- 2C with 1.5C
typical. Higher performance packs can take the higher rates. See what the
maker recommends. This way you can get in your flight, then put the battery
on a charger and be ready to fly that pack again in 15 minutes to an hour.
Have 3-4 packs and 2 field chargers and you may never have to stay on the
ground for more than a few minutes. That's the way I do it.

Lithium motor batteries are becoming popular. However their chemistry is very
different from NICD and NIMH cells. As a result they need a different type of
charging process. If you are using Lithium packs, you MUST use a charger that
is specifically designed to charge lithium or you could end up with an
explosion and/or a fire. This is not joke. Don't ever put a lithium pack on
a charger that is not designed for lithium cells. Follow the charge rate
recommendation of the battery maker carefully!
Video of a lithium battery being overcharged.
http://rc.andersh.com/video/lithiumbattery.wmv

S and P terms

When we talk about battery packs, a designation of XSYP is sometimes used.
This indicates how may cells are in serial and how many groups of these cells
are connected in parallel. While the terms are most common in the Lithium
world, they can just as easily be applied to NIMH or NICD packs.

So a 3S2P pack is made up of 6 cells. There are two groups of 3 cells. The
three cells are connected in series. This is the 3S designation. When
connected in series their voltages add. So 3.7V Lithium cells in a 3S
configuration would have a voltage of 11.1V and be designated as a 3S1P pack.
If these cells were rated at 2000 mah each then this would be a 3S1P 11.1V
2000 mah pack.

Now if we took two of these 3S1P packs and connected them in parallel, the
capacity adds, not the voltage. So this would now be a 3S2P pack rated at
11.1V and having a capacity of 4000 mah. Like connecting two gas tanks
together. The motor in you truck would not be stronger but you could drive
further because you are carrying more fuel.

You could do the same with NICD or NIMH packs. An 8 Cell NIMH pack of 1.2V
cells is rated at 9.6V and could be designated as a 8S1P pack. You are not
likely to see this, but it would still be accurate to designate it this way.
It is like Sr. and Jr. on my name. My Dad was not a Sr. until I became a Jr.
There were not 8S1P designations for NICD or NIMH until the lithium's came
along. You are still not likely to see it for the NIXX packs.

Battery Chargers

There are timed chargers and peak chargers. Timed chargers, often bundled
with RTF airplanes, work well if you always run your pack all the way down.
Otherwise they can have a tendency to over charge the packs. If you have one,
run your battery down and go ahead and use it, but I don't recommend you go
out and buy one. Peak chargers, are the way to go. They read the pack and
know when it is fully charged.

An AC powered charger is convenient to use at home, but won't help you
recharge at the field. A DC peak charger that can run off your car battery or
a flight box battery will allow you to charge at the field. There are AC/DC
chargers as well. All of mine are DC peak chargers except for my radio
chargers. I have a car booster pack that runs my DC equipment in my shop.
And, by the way, I have used it to jump start cars. Works great! This is
similar to the one I have.
http://www.sears.com/sr/javasr/produ...id=02871472000

While many peak chargers are focused on charging motor packs, most also have
low charge rate settings that can be used to charge receiver packs so you can
use them at home, or in the field to refresh you radio or receiver pack at the
field during a break.

Here are a few examples of peak chargers for your consideration. I have the
first three shown here.

HobbyZone Peak Charger - $19
Simple and inexpensive - I have 2 of these from my Aerobirds I added
different types of connectors so I can use them for all kinds of battery
packs. They work just fine. 4-7 cells NIMH and NICD
http://www.horizonhobby.com/Shop/ByC...ProdID=HBZ1026

Hitec CG-340 - $39 I have had this one for 18 months.
Does not come with charge leads - You need to make or buy leads
Easy to use for NIMH and NICD - up to 16 cells - More flexible than the
HobbyZone charger and it handles larger packs. I feel it gives a better peak
charge. It can also charge at higher currents, especially for NICD batteries.
http://www.horizonhobby.com/Shop/ByC...rodID=HRC43340

Triton Charger - $130 - This one showed up under the Christmas Tree - :-)
Better than the CG-340. It handles up to 24 cells NICD/NIMH cells or 4 cell
Lithium cell packs as well as Lead/acid field box batteries.
It will also cycle battery packs which my others will not do. So far I am
very happy with it.
http://www2.towerhobbies.com/cgi-bin...&I=LXCJG7&P=ML
Reviews
http://www.rcbatteryclinic.com/triton.htm
http://forums.radiocontrolzone.com/p...d.php?t=135705
http://www.rcuniverse.com/product_gu...product_id=19\

I don't have these but have heard good things about them.

GWS MC 2002 Peak Charger - $49
Seems to be a good value for a first charger for NIMH and NICD packs of 4-12
cells. It has charge meter, but not the digital display or memories of the
Triton or others. Includes a variety of connectors. It can not slow charge
receiver/transmitter packs due to 90 minute charge time cutoff.
http://www2.towerhobbies.com/cgi-bin...?&I=LXHHV3&P=7
http://www.horizonhobby.com/Shop/ByC...ProdID=GWS3000
http://www.gws.com.tw/english/produc...it/charger.htm

AC/DC MRC Super Brain 969 - $95
http://www2.towerhobbies.com/cgi-bin...?&I=LXEVC7&P=7
Peak charger, Dual independent outputs to charge 2 packs of 1-8 cells, at
once.
Discharge function allows you to get the most out of your batteries
LCD screen shows: battery voltage, charge rate, peak threshold, capacity,
number of cells in pack, & elapsed time For 1-8 cells any capacity NiCd, NiMH
batteries only
Selectable charge rate with 0.1 amp increments Selectable delta peak voltage
thresholds in 5mV increments

Great Planes PolyCharge4 DC Only 4 Output LiPo Charger - $100
http://www2.towerhobbies.com/cgi-bin...?&I=LXKAU0&P=7
If you are seriously into LiPoly ( not Li-ION) This may be the charger of your
dreams. Charges 4 Lipoly packs at one time. Each charge port is limited to
30 watts, so it can charge 1S or 2S packs at up to a 3 amp rate. 3S packs can
be charged at up to about 2.5 amps and 4S packs can be charged at about 2 amp
rate. Therefore, this charger seems a very good choice for 1S or 2S packs up
to 3000 mah capacity, 3S packs up to about 2500 mah and 4S packs of up to
about 2000 mah. You can charge packs of higher capacity but it will take more
than 1 hour to charge based on the typical 1C charge rate for LiPoly packs.

If you have packs with a 2, 3 or 4P designation, this charger might also be
good for you. 3S4P packs up to about 10,000 mah would work well if each 3S
component can be charged separately. 4S4P packs up to about 8000 mah would
also work, if you can charge them as four 4S1P packs of 2000 mah each.
Discussion thread on this charger
http://www.rcgroups.com/forums/showt...4&page=3&pp=15

A review of a group of Lithium battery chargers
http://www.rcgroups.com/links/index.php?id=4676

Cheapest way I have seen to run your 12 V charger indoors is to get one of
these Field box batteries
http://www2.towerhobbies.com/cgi-bin...&I=LXL370&P=ML $18
And one of these chargers - $10
http://www2.towerhobbies.com/cgi-bin...?&I=LXL353&P=V

There are many other good chargers out there. The first three are the ones I
use every day. I have accumulated these over time as my fleet and my budget
has allowed. Each has given me good service within its capabilities.
Sometimes I have 3 chargers running at the field at one time charging motor
batteries for my parkflyers or receiver batteries for my sailplanes. I hate
being grounded. So they are put to good use.

I invite others to provide insights on the subject or to recommend chargers
that have served you well.