i have a 2.7v 270mAh 6 cell battery for my slow stick and the charger i have has different amp settings, the default is 3 amps, is this a good charging rate, or should i increase/decrease it?

thanks

I would definitely decrease it. What type of battery is it (Nicad, Nimh, Lipo...), and what other charge rates do you have on your charger?

-Clint H

You do mean a 720mah battery, right? 3 amp charges will not be good for the battery!

And hopefully he means 7.2volts!

OK, let's summarize.

we presume the battery is 7.2V which would be a 6 cell pack
Is 270 MAh the right number, or is it 720 mah?
Is it NICD or NIMH?

Assuming it is NIMH and 720 mah, you would charge it a 720 mah or the closest setting you have. You might be able to push it to 1 amp/1000 mah. Most current NIMH packs can be charged at 1.5C

If it is 270 MAH NIMH pack, then you would want to keep the charge rate down to around 300 mah as most chargers are graduated in 100 mah jumps. A high of about 350 mah would be the most I would push it.

========================

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, NIMH, 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

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. (16X.5 amps)

If you have a 1000 mah pack - any kind - and it is rated at 8C that means it
can deliver 8 amps. (8X1 amp)

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