Now I'm working on my project which contains Arduino, LCD, electromagnetic lock, and 500V isolated converter. My project was designed to power by using a power bank. Now I use eloop E14 20000mAh power bank which can provide 5V 1A and 5V 2.1A so, I use 5V 1 A to powering the Arduino via USB and 5V 2.1A power the circuit. In the circuit part firstly the LCD consumes current about 200-300 mA and the voltage must maintain around 4.75 to 5.25 V. Next the electromagnetic lock consumes 12V 200mA so, I increase 5V to 12V by using a 5-12 converter that can withstand around 1-2 A. And the last one 500V converter that uses the input of 12 V then boost to 500V and this converter consumes 8mA. The question is when I started to supply my circuit the voltage will drop to less than 4.75V so that the LCD will shut down. Can anyone tell me why is this happen?. I have calculated the total current of 5V 2.1A port which is about 508mA ( less than 2.1A). According to my understanding, I reckon that the 5V will start to drop when we supply the circuit that exceeds 2.1A, so why is this happen. Lastly, I power my circuit via USB-micro USB. Any assistance will be appreciated. Thanks
Why not confirm your calculations with actual measurements? You may discover all is not as the specifications show.
Paul
Yes. All of the current mentioned above were measured by using a multimeter.
when I started to supply my circuit the voltage will drop to less than 4.75V
It all seems pretty normal. If I understand the term correctly, a powerbank's job is to charge a 3.7v battery, and it sounds like it will do that just fine.
You might need to be more forthcoming on what your intentions are, the components you are using, and how they are connected.
Probably voltage drop in your cable and micro usb connector. Have you measured the actual voltage st the battery?