Solar Powerbank Teardown
I bought this for a friend and she said she only used it once and it stopped working. So I got it back to take apart and hopefully try to fix it.
It is a typical solar power bank that can be charged from solar (very low rate - it will take a long time!) or via USB. It also has dual USB outputs and a flashlight using a single 5mm LED.
The powerbank itself. The advertised capacity varies from 20,000mAh to 60,000++mAh depending on where you look.
Looking at the size, and understanding chinese ratings, this is obviously not true.
Under the rubber surround, there are hidden latch clips to open the case.
With the case opened, we are greeted with a simple assembly. One board has all the electronics, a LiPo cell (no built in protection PCB) and a solar panel with ten polycrystalline cells estimated to be 5V 100mA output.
The cell is measured to have a capacity of 2687mAh discharged at 1A to 3.0V.
Other side of PCB
The PCB uses an ASIC of sorts in a SOIC16 package. It does not have any markings whatsoever.
I figured out that the separate protection circuitry (DW01 based) is latched open. So I used my pair of tweezers to short out the protection mosfets and jumpstart the circuitry.
A small spark and a puff of magic smoke came out of the main ASIC.
Surprisingly, the circuit now works. Indicator lights work, flashlight works except for the 5V output which is only about battery voltage and the IC gets really hot.
Here is a thermograph of the IC.
In standby mode, the circuit draws 20mA (which should be less than 0.1mA) and it draws 160mA when the lights are on.
I unmounted the inductor to see if there is any change so that I can simply use an external boost PCB but it did not help so I also unmounted the IC to check out the pin configuration.
There is a AP5901A text under the IC so I googled it and found an ASIC specifically designed for power banks. There is also this basic application schematic for it.
Online pics of an alternate package shows the same IC in a TSSOP package with an exposed pad on the bottom for heatsinking. The IC used here does not have this exposed pad which I think is the cause of failure due to overheating. The PCB also uses a 0.03ohm current sense resistor rather than the suggested 0.05ohm shunt which means current limit trip point is higher than recommended.
I do not recommend using fast charging loads on it, devices that draw more than 500mA total from both USB output ports. You might get away with 1A total (max rating of the IC) but I can't guarantee its longevity.
A bigger shot of the LED indicator side.
There is a heat dissipation area without solder mask just above the SUN- solder pad but it is useless as the IC does not have the exposed pad under it.
The IC also has a built in 1A linear Li-ION charger circuit and a TP4056 equivalent charger (which has an exposed pad) gets really hot when charging, so this could also be another cause of failure. No way of dissipating a lot of excess heat when charging from USB.
It has basic over and under voltage protection for the LiPo cell but no thermal sensing whatsoever. Since it uses a very specific application IC, there is either little to go wrong or little chance of fixing it unless you have the exact part to replace it with.
Having a solar cell on it means you have to put it under the sun for it to charge which exposes the LiPo cell to extreme heat which is not good for it. I recommend to use the USB charging only most of the time using a long thin USB cable to help dissipate most of the voltage (and limit overheating of the IC) and use solar only to keep it topped up or in worst case situations where there is no available power and you really need to make that important call.
Page created and copyright R.Quan © 29 Nov 2015.