Power problems: LiPo Battery charger and Duracell Powermat

Hi, All -

I'm running into a mysterious problem with a LiPo battery and Adafruit DC/USB charger (USB/DC Lithium Polymer battery charger 5-12V [3.7/4.2v cells] : ID 280 : $17.95 : Adafruit Industries, Unique & fun DIY electronics and kits).

Here's the back story: I'm working on a project that is entirely enclosed in a glass jar, and is powered by a single LiPo battery. In order to charge the battery, I'm using a hacked Duracell powerMat inductive charging system (the jar sits on the mat to charge the battery, and the "receiver" coil of the powermat (taken from an old iPhone case) is glued to the bottom of the jar, with a wire running to the Adafruit USB/DC LiPo charger through a hole drilled in the glass.

To get a sense of what I'm trying to do, you can see video documentation of the project here:

Here's the problem: this system works beautifully to maintain the charge of the battery—but if the device is picked up from its cradle and used long enough, the LiPo will drain to the point where its onboard undercharge protection circuit kicks in, and once that happens, I can no longer recharge the battery using the powermat. The Adafruit charger won't start delivering power to the battery again until I take the device out of the jar and plug it into a wall wart.

I think what might be happening is that the power mat can't supply enough current to override the protection circuit, but I'm not entirely sure. (FWIW, the battery is a 1000 MaH Lipo bought from SparkFun: Lithium Ion Battery - 1Ah - PRT-13813 - SparkFun Electronics)

Does anyone on the forum have experience with something like this? I'm beating my head against a wall here trying to figure it out.


Draw a schematic with pen and paper and post a photo of it.
If the problem is a hardware issue we need a schematic to see how you wired everything up.
If you're using a Lipo battery you should have a comparator voltage monitor circuit to alert you when the voltage drops too low.
You could have it turn on a LED and piezo beeper if the voltage drops too low.


The adafruit website lists that any wallwart adapter from 5v to 12v will do and also the USB socket can be used to charge ,so both of these 2 different options makes us looking at a minimum voltage threshold of 4.5 to 5.5vdc (depends on pc to pc hardware on usb output voltage) meaning that the board works with at least a minimum of 5vdc input to charge the single cell lipos.