Charging Rate (C-Rate)
Charging speeD

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What is the C-Rate?

Charging Rate and Discharging Rate

They are the same: C-Rate, C-Coefficient and C-Factor

The charge and discharge rates of a battery are determined by C rates. The capacity of a battery is usually specified as 1C, which means that a fully charged battery with a capacity of 1Ah will deliver 1A for one hour.

The same battery discharged at 0.5C should deliver 0.5A for two hours, and at 2C it will deliver 2A for 30 minutes. 

Losses during rapid discharges reduce the discharge time, and these losses also affect the charging times.

The same battery discharged at 0.5C should deliver 0.5A for two hours, and at 2C it will deliver 2A for 30 minutes.

The C-rate (Charging rate/Speed) is the ratio between current and capacity [I/Ah]=[1/h] At “1 C” a battery with1.0 Ah capacity delivers 1.0 A electric current for 1 hour

The C-rate is derived from Coulomb’s law, which was developed by the French physicist Charles Augustin de Coulomb. The C-rate is the decisive measure for the current I with which a battery is charged or discharged.

 

The mAh number of a battery indicated in each case is, among other things, the 1C number. If a battery is listed as 2000 mAh, then its 1C rating is 2000 mAh.

For simplicity, the battery should provide 1C of current for one hour. In our example above, that would be 2000 mAh or 2 A of current for one hour. The same is true for a 0.5C rating. Again, the 2000 mAh battery would supply 1000 mAh or 1 A of current for two hours.

Battery Capacity and Energy

Battery capacity and the amount of energy a battery can store can be measured with a battery analyzer. The meter discharges the battery with a calibrated current, measuring the time until the final discharge voltage is reached. For Li-ion, the voltage is 3.0-4.2 V per cell.

If a 1Ah battery delivers 1A for one hour, the meter, which displays the results as a percentage of the rated output, will show 100 percent. If the discharge lasts 30 minutes before reaching the end-of-discharge voltage, the battery has a capacity of 50 percent. 

What is the C-Rate, the C-Coefficient, C-Factor, What is the C-rate, Charging Speed, Charging rate.

Overrated and underrated batteries

A new battery is sometimes overrated and can produce more than 100 percent capacity; others are underrated and never reach 100 percent, even after discharge.

When discharging a battery with a battery meter that can apply different C rates, a higher C rate will give a lower capacity reading and vice versa. If the 1 Ah battery is discharged at the faster 2C rate, i.e., 2A, the battery should ideally deliver full capacity in 30 minutes. 

The total should be the same because the same amount of energy is delivered in a shorter time. In reality, internal losses convert some energy to heat and reduce the resulting capacity to about 95 percent or less. Discharging the same battery at 0.5 C or 500 mA for 2 hours will likely increase the capacity to over 100%.

Internal capacity and energy losses

When discharging a battery with a battery meter that can apply different C rates, a higher C rate will give a lower capacity reading and vice versa. If the 1 Ah battery is discharged at the faster 2C rate, i.e., 2A, the battery should ideally deliver full capacity in 30 minutes. 

The total should be the same because the same amount of energy is delivered in a shorter time. In reality, internal losses convert some energy to heat and reduce the resulting capacity to about 95 percent or less. Discharging the same battery at 0.5 C or 500 mA for 2 hours will likely increase the capacity to over 100%.

To get a good capacity value, manufacturers usually rate alkaline and lead-acid batteries at a very low 0.05C or 20 hours of discharge. Even at this slow discharge rate, lead-acid batteries rarely reach 100 percent capacity because they are overrated.

Smaller batteries are given a discharge rate of 1C. Due to the inert behavior, lead-acid is rated at 0.2C (5h) and 0.05C (20h).

Charging speed / discharging speed

While lead-acid and nickel batteries can be discharged at a high discharge rate, the protection circuitry prevents the lithium-ion power cell from discharging at more than 1C. Nickel, manganese and/or phosphate active material can tolerate discharge rates up to 10C, and the current threshold is set higher accordingly. 

High C-Cate Batteries & Supercapacitors

There are also specialty batteries that accept higher
C- rates up to 30C ! Supercapacitors (supercaps) in particular can charge and discharge quickly.

Visit also wikipedia.org 

Table 1. Charging duration at various C-Rates (charging rates)

C-Rate (charging rates & discharging rates)

duration

(charging speed)

30 C

2 minutes

10 C

6 minutes

2 C

30 minutes

1 C

1 hour

0.5C oder C/2

2 hours

0.1C oder C/10

10 hours

0.05C oder C/20

20 hours

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