Inside a combined power bank and jump starter

I got this unit to explore it as an option for providing a high current 12V power supply for short term use. It's a car jump starter and USB power bank. The 12V output is direct from the lithium battery pack with no protection, so care would need to be taken not to over discharge the pack when using it as a 12V supply.

The connector is a standard EC5 high current battery connector, which is handy. The USB connector has floating data pins, so it may not be recognised by some devices.

It's a very modular design. A microcontroller that displays charge level and controls the buck regulator for the 5V output that is also used for the LED, and a current regulator for charging the lithium pack that has a three cell protection chip and matching charge/discharge control MOSFETs. One oddity is the use of the microcontroller to directly drive the charging buck regulator's MOSFET.

The Battery pack has a four pin connector for charging and monitoring individual cell voltage. There's no balancing, just a shut-off when one of the cells reaches about 4.25V. It also has the high current connector tapped directly across the pack that then feeds a plug-in jump start module that contains the anti-reverse charging diodes and the MOSFETs used to switch the output to the beefy alligator clips when a separate microcontroller detects that suitable conditions have been met.

The lithium cells used in these are usually the high current type that have a different internal construction from normal cells. Instead of the electrode foils being long spiral-wound strips, the high current cells often have a stack of alternate layers of electrode foils and dielectric separators with a cluster of parallel tabs brought out the end of the cell. This allows discharge at very high currents, in brief bursts of hundreds of amps.

It looks a fairly sensible design, but as with most of these jump starters it's only really suited to an occasional quick jump start as opposed to endless cranking of an engine with issues that caused the car's battery to go flat in the first place.

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