Really Cheap Powerbanks
I got these really cheap powerbanks (less than $2 wholesale!) knowing what to expect inside but I needed them for the case and PCB for a project, and I wanted to show you guys what you get for $2!
These are the cheapest that I know of and the build quality and feel of the product shows it. It does work though (but not sure for how long) so it has that going for it.
I got several of them and there are two versions.
One is a slim version with a lipo/prismatic li ion cell. The other uses four 18650 cells.
128Ah and 2amp charge/discharge? For $2 each! What a bargain!
Made in Korea? Yeah.. okay.
Let's pop open the slim one first.
Popping the bottom cover off to get the guts out.
Pulling the guts out of the extruded aluminum case.
With the guts all out, we get a good view of what we get for the price.
The battery is a cellphone type pack with wires soldered to the contacts.
The back side has a stainless steel plate to add weight and thickness to the thin undersized cell.
With the plate peeled off, we see more specs of the chinese battery.
It is rated 2200mAh but I have measured it to be 1632mAh actual.
The PCB uses a single chip solution. It is numbered TPOWER TP4371B but I could not find info in google.
I have several of these prismatic cells. These are rated 3.85V 4040mAh 15Wh from an ASUS battery pack.
It fit perfectly!
Time to charge and use it.
I like the form factor.
It is slim and tucks behind my phone while holding them together to charge.
Now the fun part, the big one!
This one needs the front plate to come off then push it down to get the guts out.
Four 18650 cells. Hmm, why are two a different color?
Only the two blue cells are connected. Why are the other two cells left unconnected? I'll show you in a minute.
Removed the crappy cells out.
The two parallel cells measured 1626mAh total! For two 18650 cells!
Even the two crappy cells are different.
Top side too.
This one used a SOIC8 chip but still managed to cram all the same functionality in it.
The chip is marked SY3511D. Google doesn't show data too.
Replaced the cells with LG cells from laptop packs.
Grinder fixed the misleading capacity label.
Now, what is the deal with these two, you ask?
Removing the plastic sleeving, what do you see?
Top cap is not even crimped! Why?!?!
These cells are dummy cells for the sole purpose of adding weight.
The sand might even be from what they took from the western territories of my country. Ooooooh!
They do what they are supposed to and for the price you couldn't (shouldn't) complain. Both versions charge at about 950mA and then drops to about 750mA when the chip gets hot. Output current are also both limited to 1A. Greater than that, they shut off. With 5V input, TP4371B chip drops the output to about 2.4-2.8V, while the SY3511D chip, output is totally shut off. Output is resumed when charging plug is removed.
They work ok but being a one chip solution with all the hot devices in one small chip, one part fails, the whole thing is paperweight.
Now, what to do with the fake 18650 cells? I've got an idea.
Threw away the sand. Drilled a hole on the side and the plastic cap.
Attach wires and alligator clips.
Heatshrink and you're done.
A couple of handy 18650 adapters so I can charge/test pouch and prismatic cells on my LiitoKala charger!
I opened the other two powerbanks bought at the same time from the same store and there were surprises.
This one had a tiny cellphone pack with a couple steel plates for weight!
Battery and plate sandwich.
This is the cell they used. A tiny 1800mAh pack.
The PCB was also different from the other big bank. This used the same chip as in the slim bank.
USB jack tabs were not soldered. this will break the connection joints down the road.
Some used Sanyo cells to replace the tiny cell.
Third thick bank. This looks like they used real cells?
They are all interconnected. But...
The welds were not too good.
The two cells are the same dummy sand filled ones as underneath the positive contact, there is no CID, just a plastic disc.
The cells did measure better than my used Sanyo cells so I reused them.
05 Jan 2017:
Bought some more of the slim powerbanks as I like the form factor.
Opened them all up to find they all had different cellphone batteries in them.
Only thing they had in common was they all had the metal plates added for weight.
The cellphone batteries ranged from 1450mAh to 2200mAh rated. But they all appear to be used cells from old phones as one had a 2013 date.
I decided to check chip temperature and the IC measured 91degC on output mode with a smartphone charging at 1A.
When the powerbank is charging, chip temperature reaches 103degC.
Notice that the hotspot moves to a slightly different part of the IC.
This was to test one is charging, the other is discharging.
Figuring out why the chip gets really hot.
The IC does not have a heat slug underneath unlike some other high power SOIC devices.
The PCB does have a ground plane both on the top and bottom side with via stitching so it could be a ggood way to dispose of heat.
Added a small blob of heatsink grease under the IC then resoldered it.
IC still gets really hot but there is a slight reduction in chip temp.
Another trick I tried in one unit was to use those rubbery silicone blocks to thermally connect the top of the IC to the metal case. It seems to work as the case gets warm during operation. I was not able to test chip temperature though.
Made a little production line going and changed all old cells to the prismatic cells that I have. I also remounted all the ICs with heatsink goop underneath.
Page created and copyright R.Quan ©24 Dec 2016.