I recently build a Li-Ion-Charger around the Maxim Max1811 Li-Ion Charger IC (datasheet: http://datasheets.maxim-ic.com/en/ds/MAX1811.pdf). The Eagle Files of my board can be found here:
The 3 Inputs to the Max1811 are determined by simple 3-header-jumpers with 5V and GND at the sides and a trace to the input in the middle, so I can jumper the inputs to VIN (5V) or GND.
The headers on the right side of the board connect to the battery terminals, the unconnected 15-pin-header on the left side has a bit of Styrofoam on it to press the terminals against the charging headers.
The 5V and GND rails are momentarily taken from an Arduino Board, which is powered by a 9V 800mA Wall Adapter.
The LED is an orange one (i think it has a min. voltage of 1.8V or something) and is hooked up to the CHG-pin via a 330Ohm-resistor to VIN.
The problem is with this LED hooked up to the CHG-pin. When the charger is in 100mA-Mode, it slowly charges the battery and the LED lights up (the battery hasn’t reached 4.1V yet). That seems right.
However when I jumper the charger to charge with 500mA, the LED only lights up for a short time (half a second max). Looks like some kind of emergency cutoff of the IC to me, but the IC is not really warm (not the 125°C mentioned in the datasheet), you can comfortably touch it with a finger. I only felt the warmth when touching with my lips (with the board off power). There also seems to be no charging happening in 500mA-mode.
Does anyone have an idea why the charger doesn’t charge with 500mA?
Check the answers here: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1252925145/11. The power regulator could have problems supplying 500mA over time. That may be the issue.
Thank you for the link. I had already read it before, though now I think I’m gonna try to just hook the Max1811 directly to a wallwart to bypass the voltage regulator problem or use an extra LM317, which I have lying around (who doesn’t ;)) and which, acoording to the datasheet, can handle a maximum output current of more than 1A (under my circumstances at least).
Nevertheless, from the Arduino’s Voltage regulator’s datasheet (http://pdf1.alldatasheet.com/datasheet-pdf/view/12048/ONSEMI/MC33269D-5.0.html) it seems like the regulator could possibly deliver 500mA (or more). Depends on the IC package…
and as I’m at work an don’t have access to eagle I can’t look into the reference files to see which of the ICs above the powerjack on my Duemilanove is the regulator
Well, I’m gonna try further when I’m back home and keep you updated.
Have a nice day, Otacon2k
I tried powering the Max1811 with a little LM317T-circuit. The voltage regulator has got a heatsink and drops 9V to 4.4V, so the Max1811 runs on minimal voltage (4.35V) to minimize heat, which results in a downregulated charging current. The 4.6V voltage drop @ 500mA in the voltage regulator are near the given maximal values when not using a heatsink (if i calculated correctly), so with a heatsink added it should be ok.
The problem remains. As soon as I power up the charging circuit the orange LED flashes for a very short moment and then stops shining. So I assume it has nothing to do with the voltage supply.
Any other ideas someone? Could it be the caps’ values? This flashing of the LED somehow reminds me of a discharging capacitor…