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How to do math to figure out 1C?

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How to do math to figure out 1C?

Old 07-03-2013, 10:37 PM
  #1  
Higgins909
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Default How to do math to figure out 1C?

pretty much im looking at buying some lipos and want to figure out what 1c would be for them to see if my charger would work.

so how do you do the math?

I thought it was somthing like you take the mah

mah = 5000

then divide it by 1000

5ampH

multiply by max Crating say 20

100amps
and 1C is 5 amps
(100amps devided by 20C)


Is this correct?


looking at building a epp kit (still dont know what epp stands for XD) and it might need some light lipos that I dont have micro, looking at yak54 from hobbyking
so I can fly in my tiny back yard, mainly hovering, but also hopefully take it over to the park that is verry close (about 3 times my whole yard XD


some batteries I seen that were verry light

180mah
2cell
20C bust 45C

im lost on how to solve this 1 mainly bc im not sure if im doing the one above correctly.


Thanks,
Higgins909
Old 07-03-2013, 11:31 PM
  #2  
chuckk2
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Default RE: How to do math to figure out 1C?

A 180mah battery 1C rate is 0.18A
Lipo's generally like a 1C charge rate for longevity, even if they are spec'd for a faster charge rate.

Most chargers have a maximum charge rate that can be expressed in different ways.
Example
50W
5A

So, a 2 cell lipo, starting charge rate might be
(from storage) 3.8v x 2 = 7.6v
50 W/ 7.6V = ~6.58A, OR the maximum charge rate of the charger, in this case 5 Amps, or
the 1C rate of the battery, which ever is less.
As the battery charges, the voltage increases, and the current will fall as needed
to maintain the charger wattage rating or the maximum allowed battery voltage,
(Usually about 4.2V per cell for LiPo's.)

Near the end of the charge, cell balancing usually takes place, in order to obtain
the same charge and end voltage in all cells. This prevent overcharging or under charging individual cells.
An often left out spec is the maximum balance current capability of the charger.
A low balance current capability may not be enough to fully balance a battery with poorly matched cells in a reasonable amount of time.


Old 07-03-2013, 11:40 PM
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alan0899
 
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Default RE: How to do math to figure out 1C?

G'day Mate,
You are correct.
It's really simple, 1C is the Capacity of the battery pack, ie, 1C of an 1800Ma pack is 1800Ma, or 1.8 amps, & so on. That figure is used for CHARGING.
2C would be 2x1800 = 3600Ma, or 3.6 Amps & so on.
There are 1000Ma in an amp.
The figures you quoted 180Mah, 20C, the 20C is for DISCHARGING, so that means you can get, 20x180 = 3600Mah or 3.6 Amps out of that battery, until it's flat.

Cheers
Old 07-04-2013, 12:08 AM
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mehrshad
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Default RE: How to do math to figure out 1C?

you are correct.
5000mAh means it can source 5000mA or 5A for 1 hour. and 10A for half an hour or 20A for a quarter but the limit is the 20C or 100A for around 3minute(60/20)
So the C is the capacity of the battery and 20C or 30C or 45C is the maximum rate you can discharge it without damage.
Higher the C rating higher the efficiency of dischage(specially at high currents) and lower temp rise.
for a low current application like 5A or 10A, a 10C and 20C and 50C type are all the same....

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