NiCd/NiMH Battery Charger

NiCd/NiMH Battery Charger

Commercial NiCd/NiMH Battery Charger, As you may have noticed, are not that Efficient when it comes to charging time. There might be some expensive models but we are not referring to that. One of the solution is using Intelligent NiCd/NiMH Battery Charger created by Peter Hayles. This Efficient NiCd/NiMH Battery Charger build using microcontroller PIC 16C711. Because it will reduce the complexity of the circuit. He says that with the DIY charger he managed to cut the charging time from 4 hours to 1.5 hours max. This sound good to me.

"This cheap and easy to build NiCd/NiMH Battery Charger is suitable for automatically charging a wide range of batteries for many applications. Proper chargers are usually expensive and cheap chargers supplied with the original equipment often incorrectly charge the cells and dramatically shorten their life. This 'intelligent' charger was designed for high current and rapid charge applications such as cordless power tools and model racing cars."

USB Coin/Button Cell Battery Charger

I have designed many small footprint PIC projects (such as, pocket watches and wristwatches) but I cannot make them really portable. To make them portable, I need small power sources. Of course, Coin Cell battery would be the smallest DC source that I can buy. The problem is that a Lithium button cell provides 3 V. which is not enough to drive my projects. I thought about using DC-DC step-up converter to boost 3 V. to 5 V. However, it's a little bit complex to add DC-DC converter to the projects. Moreover, my projects consume a lot of power as they consist of many LEDs, a button battery will not last for a day. So, I stopped my think at that point.

Just recently, I have found a rechargeable coin cell battery at Sparkfun.com. It provides 3.7 V. at 200mAh. I don't know that my projects will work at 3.7 V. or not. But, I want to give it a try. For portability, I want to charge the battery from my computer's USB port. So, I designed a USB coin cell battery + charger breakout board. Like many simple battery charger, I use MAX 1555 as the controller of the charger.

The schematic:




The single sided PCB (40mm x 30mm):


The LED goes off when the battery is fully charged (but the charger is still charging).
Please note that the schematic/PCB are just the design and I haven't made it yet. The parts are ordered and I will update when I complete the hardware.