What is it?

This is a new version of LiPo charger add-on board for the Teensy 3.X based on ST Microelectronics' STBC08 linear battery charger. The charger provides the option of 300, 500 (default), or 800 mA charge current.

Aaron Ryan has created some very nice CAD models of this battry charger, see here.

For 300 mA, close the solder jumper marked 300 mA and cut the trace between the solder jumper pads marked 500 mA. For 500 mA, do nothing! For 800 mA, simply close the solder jumper marked 300 mA. If you cut the trace and wish to return to 500 mA, then you have to close the left solder jumper and open the right one. Consult the data sheet and the schematic; it's really quite simple once you have a look.

This LiPo battery charger add-on has the same convenient form factor as the popular original LiPo battery charger add-on based on the MAX1555. It mounts onto the Teensy in the same way and is functionally identical except it has no DC input and provides a greater range of charge currents. The new charger, like the old, has a red led to indicate charging, a green led to indicate power is supplied to VIN (chosen by using the slide switch), but also has a yellow led indicator for USB power good. This latter is useful to alert you to noise on the USB line, a frayed or damaged USB cord, or just the wrong USB input voltage.

The slide switch which controls power to the Teensy is improved with lugs to make the switch more robust and less prone to tearing off with rough handling.

Overall, this is a significantly improved version of a popular product that makes all of your Teensy projects easier and more convenient!

Why did you make it?

I received several requests for a LiPo battery charger with higher current since the MAX1555 is limited to 100 mA when the charge source is the USB cable. For the 40 or 150 mAH batteries I usually use for my portable projects this is no problem. But for larger projects that run from 500 mAH or even 1800 mAH batteries, the charge times would be impossibly long. This new LiPo battery charger preserves the appallingly small form factor of the original LiPo charger but provides up to 8 times the charge current. In my own experiments, a drained 350 mAH LiPo battery was charged in 75 minutes at 500 mA charge current, and in 48 minutes with 800 mA charge current. Compare this to the 400 minutes it took for the MAX1555-based charger at 100 mA and you can see the advantage of this new charger!

What makes it special?

This LiPo battery charger is just as small and convenient to mount on the Teensy as its predecessor but now can be configured by the user to provide the charge current right for most applications. Order the pc board from OSH Park and assemble your own or order the fully assembled and tested STBC08 LiPo charger from me and see what fast LiPo battery charging can do for your application!