Li-po Battery 'C' rating?

[Ken Cz]

Hi,
I am new to parkflyers and just bought an entire outfit including a 2100 ma Thunder Power Li-po.
Can someone please explain the "C" rating to me and how it matters or what I use it for?
Many thanks for the great replies on previous threads.

Ken Cz - MI .....just trying to learn at the ripe old age of 59!

[Neon_Dave]

It's nicely explained on the CBP's website (http://www.cheapbatterypacks.com/main.asp?pgid=faq&sid=646304#39), the FAQ section:

"We use the designation 10C etc to mean how much a cell or pack can discharge in amps. C always equals the capacity of a cell or pack. For example. Let use a PQ31003S pack rated for 12C. In this case C=3100mah. the number before the "C" is the multiplier. so 12 x 3100 = 37200mah. to get amps we simply divide by 1000. 37200/1000 = 37.2 amps. 1000mah = 1amp.

So for the above pack (PQ31003S) rated @ 12c we now know the max discharge rating is 37.2 amps.

Another example: a 20C 1800mah 3S pack. What is its max rating? 20 x 1800 = 36000. 36000mah = 36000/1000 = 36amps. So the 1800 3s pack @ 20c has a max rating of 36amps.

so when ever you see a C rating take the number before the letter "C" and multiply the packs capacity by it. That is it. To get amps from your new number simply divide it by 1000mah."

Hope this helps :)

[Red Scholefield]

It's nicely explained on the CBP's website (http://www.cheapbatterypacks.com/main.asp?pgid=faq&sid=646304#39), the FAQ section:

"We use the designation 10C etc to mean how much a cell or pack can discharge in amps. C always equals the capacity of a cell or pack. For example. Let use a PQ31003S pack rated for 12C. In this case C=3100mah. the number before the "C" is the multiplier. so 12 x 3100 = 37200mah. to get amps we simply divide by 1000. 37200/1000 = 37.2 amps. 1000mah = 1amp.

So for the above pack (PQ31003S) rated @ 12c we now know the max discharge rating is 37.2 amps.

Another example: a 20C 1800mah 3S pack. What is its max rating? 20 x 1800 = 36000. 36000mah = 36000/1000 = 36amps. So the 1800 3s pack @ 20c has a max rating of 36amps.

so when ever you see a C rating take the number before the letter "C" and multiply the packs capacity by it. That is it. To get amps from your new number simply divide it by 1000mah."

Hope this helps :)

And if you consistently discharge at the C rating you can expect very poor service from the pack, probably under 50 cycles. :teacher: Most of the vendors of these packs don't know any more about their performance than the people they are trying to peddle them to.

Red S.
The Battery Clinic
www.rcbatteryclinic.com

[aeajr]

Ken Cz,

This entire outfit you purchased, was it matched up by you, by some vendor or was this part of an RTF plane package. If it was part of an RTF package, I would assume the pack is adequate to the needs of that plane. If Hobby Lobby recommended the package, you are probably OK. If you made up the package yourself, take a look at this and see if you feel you did a good job.

BTW, Red's post is one to pay attention to for future purchases. He is an authority on the subject and his advice is very very good.

Red, if I have strayed in the following article, please add your comments.

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 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

Sizing Electric Power Systems -
http://www.rctower.com/forum/viewtopic.php?t=622

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

Lithium Batteries
http://www.rchobbies.org/lithium_battery_breakthrough.htm

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/

The Great Electric Motor Test
http://www.flyingmodels.org/motortest/index_e.htm

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

[Ken Cz]

Ed, Red and the others-
Thanks again for the great feedback and info.
The package I bought was actually put together by GWS but I bought it from my local dealer and he just duplicated it but with 'better' gear such as an E-Flite moter and TP Li-po - I should be fine.
Ken

[hobbypartz]

Watch this video to see Antonio explains his understanding of C-Rating

http://www.youtube.com/watch?v=yWixnDjUyss

[jonhalice]

a good question, i didn't know it .:)but now i know what is it ? thanks.

[gatrgof]

I have a 7 amp esc and a 800 15c battery, is this okay?

[fhhuber]

800 mah = 0.8 amp-hr

.8 * 15 = 12

So the max current the pack is rated for is not quite double the rated demand the ESC can handle.

The batteries should be fine if they are not too heavy for the model.

[chopper52]

Thats a fantastic Job all you guys did on the ( C ) Rating,things I could not understand,until now..Thanks for the great posts!!!!!!!!!:D