# What does C rating mean for batteries? Speed of discharge?

Discussion in 'Power Electronics' started by NuLED, Jul 12, 2013.

1. ### NuLED

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Jan 7, 2012
I know 1 C means discharge in 1 hour but don't quite get 20 C, 40 C, etc. for the same mAh capacity.

Is that a rating for the amperage it can sustain? 40 C means more amps (and thus discharge faster)?

2. ### shrtrnd

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Jan 15, 2010
Where are you getting these numbers from?
Is it 40 degrees C, which would be 104 degrees F?
Is this is theory test, or a data sheet, or what?
(Like, are we talking coulombs or some other unit of measure?)

3. ### NuLED

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Jan 7, 2012
Sorry no, the C rating is not the temperature.

I think it is a rating for continuous current ability or something like that. I *think* the higher the number, the more current it can provide.

I don't know if it means more current it can provide OR more current it can WITHSTAND (i.e., if you draw beyond that, then it blows up or something).

And I don't know if it applies in reverse for recharging, whether higher C rating allows you to recharge at a faster rate with more amperage (?) without danger.

4. ### GreenGiant

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Feb 9, 2012
the C-rate is whats called the "Charge Rate"
So if you use a C-rate of 0.5 with a 10Ah battery it will be charged in 2 hours, and you would be charging it at 5A, on the other hand charging at 2C means it will be charged in 30 minutes and youll be charging it with 20A

The original thing you are referring to is probably discharge rate, so at a 40C discharge it will discharge in a little less than 2 minutes and probably get pretty hot.

5. ### NuLED

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Jan 7, 2012
Thanks.

Seems as if these batteries can be dangerous (lethal)? Some of them seem to provide 100 amps! (5000 mAh x 20 C) but I guess the voltage is low enough not to be too deadly?

6. ### BobK

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Jan 5, 2010
Fire can be deadly at any voltage.

Bob

7. ### eKretz

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Apr 8, 2013
I always understood it as Capacity, like in mAh or Ah. So if a 2200mAh batt is charged at .5C, you'd be charging it at 1.1A. If it's discharged at 2C, it's seeing a 4.4A load, etc.

8. ### Y2KEDDIE

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Sep 23, 2012
Low voltage can be deadly if high enough ampacity I work with a battery bank where each individual cell can supply 950 amperes. We insulate the terminals, you would not want to drop a open end wrench across them!

Also, they produce hydrogen when charging, creating a hazardous atmosphere.

9. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,418
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Jan 21, 2010
You should check out a conventional submarine one day...

10. ### sirch

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Dec 6, 2012
Now that's a battery! Might even run my laptop for a few hours

11. ### Y2KEDDIE

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Sep 23, 2012
My original lead acid (plante') were 1/2 the size of the ones in your photo I've since replaced them with Ni-cads. Same capacity but 1/2 the size again. Stil 950A/hr. System is 130V, 65 cells.