LifeBox Battery Charger
d, bodnar 6-17-15
I recently purchased a LifeBox cell phone / tablet charger from Amazon. The charger is similar to many others on the market with a real twist: it is designed to be able to start a car that has a dead battery!
I was curious about how it pulled that off so I opened it up. That can be accomplished by gently prying the top off with a thin screwdriver.
The box contains a large blue battery (probably Lithium Ion), a circuit board and an LED with a lens..
The two USB sockets are at the top (left and center) and the LED is to the far left. You can see its current limiting resistor (25 ohms?)
The two inductors (labeled 4R7 and 220) are part of the power supply to provide 5 volts for the USB (4R7) and the circuit to charge the battery.
The car battery cables are a bit over 12" long. At first I thought that the large red box was a fuse...
...but after opening it I found four (there are two more on the other side) low dropout diodes that are used to interrupt current flow should the battery cables be connected to the car battery backwards. Here is the data sheet on the parts that are inside: http://www.irf.com/product-info/datasheets/data/42ctq030.pdf
Here is the side of the LifeBox with its two USB outlets, charging port and (to the far right) the car starting port.
Here is a close-up of the car starting port - the red "+" marks the positive terminal
I was curious about how the unit was dealing with the high current it can deliver. I expected some sort of semiconductor between the plugs (above) and the battery. On closer inspection I saw that there is nothing between them! The terminals go right to the battery. This close-up shows the large wires.
Since there is no auto-cutoff to the car battery port you must take care not to drain this unit below 1 LED light on the indicator or it is likely to be ruined.