J421

I'll be purchasing my first park flyer soon, and will need some extra equipment (I've had experience with 'regular sized' scale airplanes). I'm looking at batteries. (I'm either going to go with the BLT or the SLOW STICK). Which size battery is recommended?

Also, which battery type do you recommended. I've been reading about NiMH, NiCd, and Li-Po. I'm a little intimidated by what I've read about Li-Po's exploding.

Thanks

ultramag1234

nimh 8 cell 9.6volt 700mah thats wut im using. It should give you enough power for a 10-12 min flight
Mike

aeajr

My Feedback: (2)

BATTERY BASICS
by Ed Anderson
aeajr on the forums

All RC planes use battery packs to operate their electronics. On planes that
don't have electric motors we call these receiver packs as they power the
receiver and the receiver then distributes the power to the servos and other
electronics in the plane. However for electric planes, we also use the
batteries to power the motor. They are the chemical fuel tanks that store the
energy we use to fly. Each has advantages and disadvantages.


Battery Types

At the time of this writing, April 2005, there are three commonly used
rechargeable types of cells. They vary by the chemical mix that is used to
hold and deliver the electricity to the motor of the plane.

Nickel Cadmium, NICD, have been in around the longest.

Nickel Metal Hydride, came in to use later and are very popular today.

Lithium cells are typically lithium polymer, LiPoly or LiPo, and the less
commonly used Lithium Ion. These are the newest breed of chemical cells.

NICD packs have the lowest power to weight ratio. That is to say that, for a
given capacity they will weigh the most of the three types. However they have
the ability to be charged faster than the other two and will give up their
power fastest. While still in common use, the are dropping in popularity as
the other two types are improving and gaining on NICD's advantage of quick
charge and quick discharge. Each NICD cell is rated at 1.2 volts.

Nickel Metal Hydride, NIMH, packs hold about 40-70% more capacity per ounce
than NICDs. So, for example, a 900 mah NICD pack might weigh 6 ounces while
an equivalent capacity NIMH pack might be 3.5-4 ounces. However NIMH packs
can't quite match NICDs for how fast they can deliver their electricity or how
fast we can charge them, but they are catching up. There used to be a big
gap, but the gap is closing fast. NIMH are far more popular today then they
were just a few years ago, and probably have passed NICD in usage. Each NIMH
cell is rated at 1.2 volts, the same as NICD cells.

Lithium packs are the lightest for their capacity. They typically hold 4 or
more times as much electricity per ounce as compared to NICD packs. So that
same 900 mAH NICD pack at 6 ounces would compare to a 900 mAH LiPoly pack at
1.5 ounces. However these packs have been slower to charge and slower to
deliver their power, but over time they are improving. They are growing in
popularity as the discharge rates improve and the prices come down. Each
Lithium cell is rated at 3.7 volts.


Pack Configuration

Unless stated otherwise, we join the cells into packs by joining them in
series. In series we add the voltage of each cell so that a 6 cell NICD or
NIMH pack will be rated at 6 X 1.2 volts or 7.2 volts. With lithium packs,
which are rated at 3.7 volts per cell, it would take two cells to create a
comparable 7.4 volt pack. When you hear people talk about 4 cell, 6 cell,
however many cells today, they are usually talking about NICD or NIMH cells.
However, with the rise of Lithiums, you should ask to be certain that they are
not talking about lithium cells.

Clearly if your instructions say that your motor can use a 7 cell pack, it
would be important to know if that is 7 NIMH or NICD cells or 7 Lithium cells
as the voltages would be very different. A 7 cell NIMH or NICD pack would be
8.4 volts. A 7 cell Lithium pack would be 24.9 volts.

While it is unusual to combine NICD or NIMH packs in parallel to increase
capacity, it is quite common with Lithium packs. This has spawned the xS xP
designation, were the first x is how many cells connected in series and the
second is how many groups of these cells are connected in parallel. So a 3S2P
pack would have two groups of 3 cells. This allows us to deliver higher
amperages at the same voltage, or to provide more capacity for longer flights
at the same voltage. The xSxP designation is most commonly used with Lithium
packs.

Battery Chargers

When charging your battery packs you MUST use the right kind of charger or you
will damage the cells. Using the wrong charger, especially with lithium
cells, can actually lead to a fire or an explosion. So be sure that you have
the right charger for the kind of cells you are charging. Some chargers are
made for one kind of cell, some can charge two kinds of cells and some can
charge all three. Make CERTAIN you know before you charge or you could put
your model, your care, your home or your personal safety at risk.

I hope this has been helpful. Below are some additional resources for
further reading.

Excellent overview and safety information on Lithium Batteries
http://www.*********.org/lithium_bat...eakthrough.htm

More on Batteries
http://www.modelaircraft.org/mag/FTGU/Part8/index.html

New Electric Flyer FAQs
http://www.ezonemag.com/pages/faq/a105.shtml

aeajr

My Feedback: (2)

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=LXN66&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 makes 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. NIMH packs are best charged at 1- 2C. 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


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 charters for your consideration. I have the
Triton, the Hitec and the HobbyZone chargers.

HobbyZone Peak Charger - $18
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 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
Pirana or others. Includes a variety of connectors. It can not slow charge
receiver/transmitter packs do 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

Dymond 1-12 Cell DC/DC Booster Charger $55
DC Charger - Fast and trickle charge of 1-12 cell
NiCad and NiMh batteries Adjustable 0.3-4.2 amp
http://radicalrc.secure-mall.com/sho...=1&cart=280242

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.

aeajr

My Feedback: (2)

This note is intended to clear up a few terms and concepts around electricity
as it applies to electric airplanes.


Think of electricity like water. Volts = pressure Amps = flow

Volts is like pounds per square inch, psi. Says nothing about how much water
is flowing, just how hard it is being pushed. You can have 100 psi with zero
water flow.

Amps is flow, like gallons per hour. You can have flow at low pressure and
you can have flow at high pressure.

Amp hours is how much flow can be sustained for how long. It is used as a
way of measuring how much electricity is in the battery. Like how many gallons
of gas in your tank. It is a capacity number. Says nothing about flow or
pressure, it is about capacity.

Amps and mili amps? We are just moving the decimal point around.

1 amp (short for ampere) - 1000 miliamps (mili means 1/1000)

Examples

So a 7 cell NIMH or NICD pack provides 8.4V (pressure).

The motor will draw electricity from the pack at a certain flow rate, or amps.

If you have a have a 650 mili amp hour pack, it can deliver a flow of
.650 amps (650 miliamps) for one hour. If you draw it out faster, it doesn't
last as long. So your motor might pull 6.5 amps for 1/10 of an hour, or about
6 minutes.

A 1100 mah pack has double the capacity of the 650 mah pack, so it should
last "about" twice as long.


What is C in relation to batteries?

C ratings are simply a way of talking about charge and discharge rates for
batteries.

1C, = 1 time the rated mah capacity of the battery. So if you charge your 650
mah pack at 1C, you charge it a 650 miliamps, or .650 amps.

1C on a 1100 pack would be 1.1 amps.

2 C on your 1100 pack would be 2.2 amps

Motor batteries are often rated in Discharge C and charge C.

So a 1100 mah pack (1.1 amp hour) might be rated for 10C discharge, so you can
pull 11 amps ( flow ) without damaging the battery.

Then it might be rated at 2C charge rate (flow), so you charge it at 2.2 amps
(2200 mah)

How did I do? Things clearing up?

If you have a 500 mah pack - any kind - and it is rated at 16C that means it
can deliver 8 amps.

If you have a 1000 mah pack - any kind - and it is rated at 8C that means it
can deliver 8 amps.

If you have a 1000 mah pack - any kind - and it is rated at 12C that means it
can deliver 12 amps

If you have a 1500 mah pack - any kind - and it is rate at 8C that means it
can deliver 12 amps

If you have a 1500 mah pack - any kind - and it is rated at 20 C that means it
can deliver 30 amps.

If you have a 3000 mah pack - any kind - and it is rated at 10 C that means it
can deliver 30 amps.

So, if you need 12 amps you can use a pack with a higher C rating or a pack
with a higher mah rating to get to needed amp deliver level.


One last point. Motor batteries vs receiver batteries

Some batteries can sustain high discharge rates. Others can not.

Those used as transmitter/receiver packs typically are made for low flow/amp
rates while those made for motor packs can sustain higher rates.

So, having a 600 mah pack does not tell you if it is a motor pack that can put
out 6 amps, or if it is a transmitter/receiver pack that would be damaged if
you tried to pull power at 6 amps. It is enough to say that they are
different.

Clearly a motor pack could be used for a transmitter/reciever job, but a
transmitter/reciever pack should not generally be used as a motor pack.

Basics:
http://www.modelaircraft.org/mag/FTGU/Part8/index.html

Lithium Batteries
http://www.*********.org/lithium_bat...eakthrough.htm

New Electric Flyer FAQs
http://www.ezonemag.com/pages/faq/a105.shtml

J421

wow, thanks for all the info! After reading it, I'm wondering about my radio system. I purchased the Futaba 7CAP a few weeks ago, to use on my P-51 I'm building. The futaba setup came with two batteries - one for the transmitter and one for the receiver. It also came with a basic charger that has 2 leads on it, so it can simultaneously charge the two batteries at once. Is it possible for this charger to do damage to the batteris?

Thanks again

J421

I think I'll stick with a nimh or a nicd. NiMH and NiCd batteries do not have the risks that Lithium batteries have, right? I've been reading that lithium batteries can cause a possible fire. Can NiMH and NiCd batteries also cause a fire? Are the odds the same?

INeedHelp

My Feedback: (1)

Alot of the problems with li-poly batteries are operator error. Charging a 2-cell as a 3-cell or something like that. I have been using lipo's since I started flying over a year ago and in well over 100 crashes i have yet to have any issues with them. That being said the manufactures have to give all the possiblities of using their products so they are not liable for any misuse by the consumer. Actually in the last year I have heard of more nicads exploding than lipo's.

blueberry

Ed,

Thank you very much for your post. I am just getting into electrics, and I was not sure how the C - rating related to amps on the li-poly batteries. Your very informative post has cleared that up!

Thanks again,

Pete