fristCase brief (Customer request)
6pcs USB ports are needed, and it could charge 6pcs mobile phones at the same time. Box should be as thinner as possible and with indicate lights and switch on/off. This power bank will be put into a backpack and will be fixed by a slot on the backpack, so when design the size, we need to tack the backpack size into consideration. People will carry this power bank to remote place all over the world to test the mobile phone signal, so we need to keep the calorific value small, thus to keep it work for 6 to 8 hours, and we need to add a charger for this power bank..
Solve the case (case analysis)
1.Difficulties:
①The box should be as thinner as possible and the customer doesn’t want to open new mould because it’s costy, so we need to try our best to find a suitable box.
②In order to charge 6pcs mobile phones at the same time, the output voltage should be 5V and stable and the PCM should be developed as customer’s request.
③We need to add indicator lights to show the capacity, a charge port, and a switch on a small place and make sure it looks beautiful and reasonable.
2.Key points:
① Optimizing the structure of PCM and battery pack.
②Parameters of the PCM should comply with customer’s request.
③Make sure no deviation when drilling holes on the box.
Set up the project (project design)
1.Ideas for desing:
①Choose suitable box and confirm the size with our customer.
②Think about the display way and space for PCM after confirming battery capacity.
③Temperature can’t be too high, capacity should be enough for keeping the power bank work for 6-8 hours after fully charged. The charge current can’t be too large and charging time can’t be too long, so we are going to make it to be a 2S battery pack on the premise that the power value of the battery won’t change, then we need to make the battery with reduction voltage function with 5V output.
④To make sure the drilling precise, we use CNC technology.⑤Confirm the printing on label and send it to printing factory for production.
2.Concrete plans:
①Case NO. is 3204-1;26.4Ah 7.4V power bank.
②Battery cell: BAK brand 18650 2200mAh 3.7V, 24pcs totally.
③Structure of battery pack: 2S12P,24pcs 18650 battery cells, capacity of each cell is 2200mAh. Final voltage:7.4V, final capacity:26.4Ah.
④PCM requests:
Charging: input voltage 12V/3A, 0.3A trickle, 3A constant current, 8.4V constant voltage.
Output: Six USB ports, output of each port is 5V/1A, no auto power-off function when it’s no load, should be operated by hand. With 20 hours timing shutdown function, static current no more than 100uA.
Switch on/off: only one, long press for about 3s to turn on/off.
Display: Red LED lights on when charging, turn off when it’s fully charged. Totally 4 LED lights, each light represents 25% capacity and will turn off according to the capacity one by one. It will flash when the capacity is low, frequency is 1HZ.
Protection: with over current, over charge, over discharge and short circuit protection function.Output discharging efficiency≥85%.
⑤Outer box is creamy white, size is about 55*150*220mm.
Implementation (process introduction)
1.Drill holes on outer box.
2.Match groups for battery cells.
3.Insulation and assemble battery holders.
4.Make the battery cell in series and parallel with nickel strips.
5.Add PCM and testing the performance.
6.Insulate and fix the battery into box, assemble box, indicator lights and switch on/off.
7.Test and add labels.Do CE-EMC,UN38.3,MSDS testing .
Validation (difficulty and keynote)
1.Whether it can charge 6pcs mobile phones in the same time and compatible for different mobile phone brands.
2.Whether it can be fully charged by a 12V adapter.
3.Capacity indicator lights works or not
.4.Switch on/off works or not.
5.Assemble batteries and testing pictures are as below:
