C-rates are useful in determining which battery is best for your operation, e.g. Table of battery comparison, especially in conjunction with the battery capacity.
Battery capacity is the Amp-hr (Ah) rating of a battery and describes how long a battery can provide a certain current (A). For example, a 100Ah battery can provide 100 Amps to a system for 1 hour (100A x 1hr = 100Ah), or 50 A for 2 hours (50A * 2hr = 100 Ah), or 10A for 10 hours (10A * 10hr = 100 Ah).
C-Rate is a measure of that battery capacity rating. A battery that is rated to discharge its total capacity (Ah) in 1 hour would be rated at 1C, or in 2 hours would be rated at .5C, or in 4 hours would be rated at .25C, or, in the faster direction, in 30 minutes would be rated at 2C. See Table 1 for some examples.
Because of internal resistance loss and battery chemistry, a battery rarely delivers nameplate rated capacity in only one hour (1C) and typically maximum capacity is found at a lower C-rates. Plus, faster charging and/or discharging (aka at a higher C-rate) typically reduces the total capacity and lifespan of a battery.[1][2]
| C-Rate | Rated Capacity (Ah) | Average Current (A) | Charge (or discharge) Time |
|---|---|---|---|
| 5C | 50 Ah | 250 A | 12 min |
| 2C | 50 Ah | 100 A | 30 min |
| 1C | 50 Ah | 50 A | 1 hour |
| .5C (aka C/2) | 50 Ah | 25 A | 2 hours |
| .25C (aka C/4) | 50 Ah | 12.5 A | 4 hours |
| .1C (aka C/10) | 50 Ah | 5 A | 10 hours |
Battery manufacturers often publish datasheets with graphs showing capacity versus C-rate curves. The C-rate is also used as a rating on batteries to indicate the maximum current that a battery can safely deliver in a circuit. So a battery rated at 1C on the battery, indicates that it can safely discharge its full storage in 1 hour. Some batteries, e.g. Lead Acid Absorbent Glass Mat (AGM), typically have a low C-rate of about 0.25C (safe and efficient charging or discharging of the rated storage over a 4 hour span), where as other batteries, e.g. Lithium Iron Phosphate (LiFePO4), can have a high C-rate of over 3C (safe and efficient charging or discharging of the rated storage in just 20 minutes!).
See more[edit | edit source]
- Table of battery comparison
- Battery temperature to capacity tables
- https://www.engineeringforchange.org/webinar/battery-fundamentals-off-grid-electrification/
References[edit | edit source]
- ↑ https://en.wikipedia.org/wiki/Electric_battery#C_rate
- ↑ Battery University - What is a C-Rate
