How to Calculate Power Bank Capacity?
The best tool to detect the true power bank capacity is to use our phones as the measure standard. I believe this is what we are most concerned about, which what you are most concerned about when buying power bank! First, we need to understand relationships between the power bank and the charger devices.
Capacity is the most important characteristic of the power bank,before buying a power bank it is better to know that the power bank can charge how many times for our device,I believe that it is one thing that we care about.Here we will teach you how to understand the relationships between the power bank and the charger devices.
1.First we should know two parameters,voltage and current.We must first know what measures the charging indicator of power bank corresponding to cell phone. There is a formula for the power bank: power = voltage * current.Cell phone batteries will be marked with it usually, the voltage of most phones is 3.7V,and the power will be marked on the phone battery!
2.Every power bank has a conversion rate.The batteries of power bank are 3.7V output, first boost to a maximum of 5V through the internal circuit control, and then charge for the phone output, so there is a certain conversion rate during the product buck-boost.Generally, the qualified power bank conversion required in this process is designed about 90%. Power bank conversion rate is also related to batteries used in the production. The polymer rechargeable batteries work output conversion rate is generally 85% -95%, and 18650 lithium battery output conversion rate is 75% - 85%. In summary, the overall conversion rate of power bank, the power bank conversion rate of better batteries produced by polymer batteries is 75% - 85%, and the conversion rate of power bank produced by 1865 batteries is 65% -70%.
3. Test conversion rate, the real capacity and charging times We can begin calculating the charging times of mobile phone,after we know the real capacity of power bank. The current of the smart phones required at charging is dynamic, normally above 500MA-1000MA, the voltage is at 5V or so. If the battery power is marked 4000 mAh, then the power of a 4000 mAh power bank should be 4 * 3.7 = 14.8W, calculate by our polymer batteries conversion rate of 80%, the real total power supply for charging can be 11.8W. Take a 1500mA smart phone for example, the demand power is 3.7*1.5 = 5.55W, then it can charge the phone two times. So if you want to charge your tablet,you need a larger capacity power bank,the power bank capacity should be more than 8000MA and can provide high current 2A output charging requirements.