A failed mobile power pack begs for a thorough perusal of its batteries and other internals.
Back in December 2015, I picked up two iWorld MPT-1200 12,000 mAh portable battery packs, intended for recharging other devices via the power banks’ three USB outputs in combination with not-included charging cables, from Meh for $25 total. The MPT-1200 intended for my wife hasn’t yet made it out of the box; mine unfortunately no longer reliably holds a charge after only limited use these past four years, so it’s time to take it apart!
I’ll begin with some packaging shots of my wife’s unopened MPT-1200:
And here are some photos of our patient (with dimensions of 5.625×2.5×1 inches, and weight of 13.6 ounces) prior to surgery. Alongside the battery pack is a penny (0.75 inches/19.05 mm in diameter and 0.0598 inches/1.52 mm in thickness, for those of you outside the U.S.) for size comparison. Not shown is the short USB-to-micro USB cable also included in the box for recharging the battery pack itself.
At the top is the power button (also used to illuminate and extinguish the “flashlight” function) along with four blue LEDs, three of them used to report stored charge level and the fourth indicating active charging:
iWorld claimed that each of the three USB outputs, when used standalone, was capable of outputting 2A of charge current, with 1A maximum output current when multiple USB ports were simultaneously in use. As you’ll see from the Meh forum discussion on the MPT-1200, that particular manufacturer spec was disputed by many of the product’s customers.
On the right side is the white LED that implements the “flashlight,” along with the micro-USB input for MPT-1200 charging purposes:
Time to dive inside. From past experience with inadvertently punctured Li-ion batteries, I was a bit skittish about cracking open the enclosure, but my worry was unwarranted. Inserting a thin flat-head screwdriver in one of the seams that circumnavigated the device, then gently twisting, initiated a sequential tab-unlatch process resulting in the complete removal of the top of the MPT-1200 in short order:
Here’s a closeup of the flexible plastic assembly that connects the power button to a switch on the PCB, as well as the openings for the PCB’s four LEDs to shine through:
And speaking of which, here’s an overview of the PCB-plus-five-battery assembly that comes into view once the top is removed:
Let’s focus first on the batteries:
As the markings suggest, they’re 18650 cells, each of which normally has a charge capacity of ~3000 mAh. Presumably, therefore, they’re connected in parallel to meet the battery pack’s 12,000 mAh aggregate rating. 18650 cells also have a 3.7V specification, therefore (obviously) requiring voltage boost circuitry elsewhere in the system design to meet the USB outputs’ 5V requirement.
Now for the PCB:
See those two Philips screws? Remove them, and the PCB lifts right out of the case bottom below it:
Here’s a closeup of the PCB topside:
IC U1 at right is a Hotchip HT4906 power management IC. To its left is U2, a Sino IC Technology SE9926 N-Channel 20V MOSFET. In the middle of the PCB is the power switch. To its left are the four charge active-and-level LEDs. And above them are two 2TY discrete transistors.
Flip the PCB over and, among other things, the micro-USB input (charging) connector, three USB output connectors, and the “flashlight” LED come into clear view. Also notable are the two ON Semiconductor SS34 3A Schottky barrier rectifiers below the middle USB connector and the ON Semiconductor SS24 Schottky rectifier diode on the right.
More generally, once the aforementioned two screws have been detached, the entire PCB-plus-batteries assembly lifts right out revealing, among other things, the battery-to-battery interconnect scheme:
To quote Porky Pig, “That’s all, folks!” As always, I welcome your thoughts in the comments!
—Brian Dipert is Editor-in-Chief of the Embedded Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.
- Introduction to lithium-ion rechargeable battery design
- Keeping it safe: The lithium-ion battery
- Do lithium-ion batteries follow Moore’s Law?
- Portable power: New lithium-ion battery chemistries allow designers to trade off energy capacity and power
- Runaway Lithium-Ion batteries
- Lithium-ion battery fires: 7 solutions for improved safety