Batteries

[monkeyjay]

Hi Guys n Girls

I am a bit confused about the numbers on batteries, I get the amphour rating and the cell number but what does the 20c or 40c etc meen and how do you work out what speed controller goes with it or vice versa? I ask because I think ive finally decided to get the axn floater so i can follow along with Bruces Bargin Bin FPV Builds as that interests me and the i will need to add a battery and tx/rx to the PNF kit and I am unsure as what to choose from the vast lists available.

All help is appreciated

Jay

[ergocentric]

Hi Guys n Girls

I am a bit confused about the numbers on batteries, I get the amphour rating and the cell number but what does the 20c or 40c etc meen and how do you work out what speed controller goes with it or vice versa? I ask because I think ive finally decided to get the axn floater so i can follow along with Bruces Bargin Bin FPV Builds as that interests me and the i will need to add a battery and tx/rx to the PNF kit and I am unsure as what to choose from the vast lists available.

All help is appreciated

Jay

The Ampere-hour rating is capacity like the surface area of the bucket
The Voltage is the height of the bucket
The c rating is a multiplier of the Ah rating telling you how fast you can safely discharge the battery, or how fast you can drain the bucket.

assuming a 3000mAh (3Ah) battery, 20c could discharge safely at up to 60A, 40c up to 120A
keep in mind the corollary, 10c gives you 6mins full power, 20c gives you 3mins full power, 40c gives you 1.5mins full power

[monkeyjay]

Hi thanks for the quick reply, I think ive got it so if i plan to add a 2200 lipo to the axn floater then for longer flight time i need the lowest "c" rating i can find, so what relation do these figures have to the ampage of a speed controller or is the relation btween that and the amps of the batt

Jay

[John_Edward]

That is wrong.

Now, there are 3 things in a battery.
Voltage is told as the number of cells, one cell being 3.7 volts.
Capacity is told as milliampere hours, 1000mAh meaning at a draw of 1000mAh, or 1A, it lasts one (1) hour.
And 'speed' or 'endurance' is told as a C rating, 10C meaning you can draw ten times its own capacity, 22000mAh, or 22Amps

So, get a battery that has:
The proper amount of cells, voltage for your electronics, 1S = 3,7V, 2S = 7,4V, 3S = 11.1v etc etc
That has the biggest mAh rating you can possibly fit in your plane, more mAh directly means longer flight-time, but increased weight and price.
And a C rating big enough for your needs, more is better, but not necessary.



And here are the details:

Your motor draws a certain amount of current, measured in Amperes, A.
The C rating tells you how fast you can draw that power.

If you have a 2200mAh, milliAmperehour battery, it means if you draw 1000mA in an hour, it should last you 2.2 hours.

So lets say you have a motor like this right here.
Its max load is 30A, meaning that at full power, it might draw power from the battery at a rate of 30000mAh, meaning it uses the 2200mAh your battery pack can give in just around 4 minutes.

Now, your battery will have to be able to give it that 30Amps it wants, and this is where the C rating come into play.
A C rating tells you how fast the battery can be drawn empty, C being the mAh capacity.
A 2200mAh battery with a C rating of 15 could give 15 times its own capacity at once.1
15 x 2200mAh is 33000mAh, or 33Amps.

[RCModelReviews]

This is one of the things I'll be covering in the first part of my "electric power demystified" series.

[jeffie8696]

The way I put it to people
Miliamphours = how big the gas tank is
Voltage = how much horsepower it has
C rating = how much horsepower it can deliver before it melts.

[francoishaha]

hi, i found a great article on WattFlyers forums, here the part that tell about Battery, realy intresting and well explaine:

AMPS vs. VOLTS vs. C
By Ed Anderson
aeajr on the forums

This brief discussion 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 amps)

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 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 delivery 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.

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/receiver job, but a
transmitter/receiver pack should not generally be used as a motor pack.

It is best to size your battery packs so they run somewhat below their
maximum C rating. You will stress them less and they will last longer. For
example, if your motor needs a pack that can deliver 10 amps, getting a 1000
mah pack that is rated for 10C ( 10 amps ) will meet the spec, but it is
running at its limit. A 15 C rated 1000 mah pack would be better, or
perhaps a 1300 mah 10 C pack. In either of these cases, the pack will be
less stressed and should handle the load much better over the long term.


Other Resources

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

Lithium Batteries
http://www.rchobbies.org/lithium_batter ... hrough.htm

Lithium Balancers and Balancing Chargers
http://www.rcgroups.com/forums/showthread.php?t=599287

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

A series of posts on electric power system basics
http://www.wattflyer.com/forums/showthread.php?t=1933
http://www.rcgroups.com/forums/showthread.php?t=417868

MotoCalc
MotoCalc will tell you everything you need to know: Amps, Volts, Watts, RPM,
Thrust, Rate of Climb, and much more! It is a popular tool for predicting
the proper motor, prop, battery pack for electric planes.
http://www.motocalc.com/


Electric Motors Described
http://adamone.rchomepage.com/guide5.htm

[Sid Sideslip]

Hi Guys n Girls

I am a bit confused about the numbers on batteries, I get the amphour rating and the cell number but what does the 20c or 40c etc meen and how do you work out what speed controller goes with it or vice versa? I ask because I think ive finally decided to get the axn floater so i can follow along with Bruces Bargin Bin FPV Builds as that interests me and the i will need to add a battery and tx/rx to the PNF kit and I am unsure as what to choose from the vast lists available.

All help is appreciated

Jay

Just to answer one question simply. For the AXN you will need a 2200mAh 3S battery with a 20C rating.

This one in fact: http://www.hobbyking.com/hobbyking/store/__16753__ZIPPY_Flightmax_2200mAh_3S1P_20C_AUS_Warehouse_.html