Bootleg Battery Charger Heart Transplant

Following on from my previous post where I looked inside a cheapo battery charger from eBay – I have since gutted the charger. All that I kept was the case and the battery contacts.

Gutting the unit eliminates a potential fire hazard. I replaced the circuitry with a dedicated lithium ion battery charger IC instead.

I’m using a MAX1555 and it is a single chip solution which requires a minimal number of external components. It is a single cell charger and has a maximum charge current of 280mA.

The chip has dual inputs, allowing you charge a battery from either a USB port or a DC plug pack. When charging from a USB port, the charge current is limited to 100mA. Whereas, the DC plug pack input allows for a charging current of 280mA. Also, this version of chip has a charge status indicator which can be used to drive an LED.

I’m not going to use the 240VAC socket anymore, and I’ve replaced it with a micro USB socket. This change lets me use a USB wall socket adapter which can deliver 1500mA at 5VDC. However, my new circuit will only require 280mA. (I’m already thinking about a 2nd iteration of this project which will use an IC with a higher charger current to charge faster.)

Schematic for the new battery charger using a MAX1555 IC.

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