# Battery "C" discharge and burst rates?



## emu26 (Jun 23, 2008)

Hi,
I was wondering if someone can explain to me in non technical terms what the "C" dishcrage and burst rates are on Li-Po batteries?

I understand how to calculate run times and if the battery will be big enough to power a certain driver / led combo but have never really understood the above?

I'm asking both in general terms, ie how its calculated, what impact on run times same capacity but different discharge rates batteries have, but also specifically so I can work out if a battery is suitable for a light I'm building for a friend. 11.1v Li-Po, 15 C discharge rate powering maxflex driven 6s XPE light.

Thanks in advance


----------



## HEY HEY ITS HENDO (Feb 23, 2008)

this is a handy guide ...

http://www.batteryuniversity.com/partthree-5.htm

.. http://www.batteryuniversity.com/index.htm


----------



## diabolicaldan (Feb 8, 2010)

in the most simple terms there should be two "C" ratings on any LiPo battery.
Max Constant C and Burst C. Burst is usually for durations of 15-30 seconds. Running a battery at Max Constant C will result in the battery getting very warm.

Here's the math.

Take the capacity of the battery (measured in mAh or milliampere hours) X (multiply) the number of C in the "C Rating" and you will have the maximum constant/burst milliampere discharge rate.

Here's an example:

11.1V = 3 cell LiPo : 2000 milliampere hour pack with a 15 C (max constant discharge )rating.

2000 (mAh) X 15C = 30000 milliampere = 30A maximum constant discharge.

Cheers,
Dan


----------



## OldMTBfreak (Apr 8, 2006)

"C" is the batteries capacity in ampere-hours. So fer instance, maybe a 2.6AH li-ion is rated 2C discharge and .5C charge. This would equal a 5.2A discharge and a 1.3A charge. As to burst rates, that's like the peak power that Sears vacuums are rated. Straight out of somebodys a$$. Always think about your battery as a piece of ice. If you need a little ice, and chop off small pieces, your ice will last for a while. If you whack off big pieces it'd gone quicker. lol The more current you draw from the battery, the more O2 ions form on the positive plate. This limits the battery's abilitity to supply current. With 6s XPG's, about 20Vf @ 1A = about 20W + a couple watts for the regulator. You'll pull about 22W from battery. A 18650 Li-ion has about 9.5WH per cell. 3s would give a 27.5WH battery. You will be drawing 22W from battery, run time a little over an hour. 3s2p will double the run time. With an 11.1 volts on hand, and (P=E X I), you will have to supply about 2 amps. This will rise to over 2.5A as the battery discharges. You will need a 3s2p battery arrangement. Oh yes, last but not least, this is for batteries at room temp; about 25°C. At cold temps the batteries wimp out. James


----------



## OldMTBfreak (Apr 8, 2006)

Thanks Hendo, I couldn't remember where the Battery U stuff was.


----------

