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Heltec-Aaron-Lee / WiFi_Kit_series

Arduino source codes and toolchain for WiFi_Kit_series made by HelTecAutomation.
GNU Lesser General Public License v2.1
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How to increase the battery charge current? #42

Open stroobandt opened 6 years ago

stroobandt commented 6 years ago

Quite a few people, including myself, are a bit disappointed with the low battery charge current of the Heltec Wifi Kit 32.

I am designing a high-volume project using the Heltec Wifi Kit 32 in combination with a 3400 mAh 3.7 V Panasonic 18650 LiPo battery.

The charge chip on the Heltec Wifi Kit 32 is a Microchip MCP73831. According to the datasheet, the charge current of this chip can be programmed with a resistor between pins 2 and 5.

On the Heltec Wifi Kit 32, a resistance of 10 kΩ is measured between these pins.

My question: What modification do I need to do in order to increase the charge current to its maximum 500 mA?

stroobandt commented 6 years ago

OK, I found the Heltec Wifi Kit 32 schematic diagram. This confirms the device comes with a 10 kΩ charger programming resistor, resulting in a charge current of only 100 mA.

I will place an extra 2.7 kΩ resistance in parallel between MCP73831 pin 5 and ground. This will result in a total programming resistance of about 2.1 kΩ and a charge current of 470 mA.

500 mA is the absolute maximum charge current allowed for the MCP73831 charger chip. The schematic is wrong in suggesting a resistance for a 1 A charge current.

stroobandt commented 6 years ago

I will place an extra 2.7 kΩ resistance in parallel between MCP73831 pin 5 and ground. This will result in a total programming resistance of about 2.1 kΩ and a charge current of 470 mA.

Doing so bricked the charging chip of my device! Apparently, the charging current came too close to the 500 mA limit. I will soon try again with a more conservative programming resistor value.