I’d like to build a circuit to charge 18650 batteries. Oddly my last project as a full time engineer was doing this for an aircraft. I COMPLETELY forgot the specifics. It was back in 2012. There were no charge IC’s then so we had to do it from scratch essentially. Long story short…
I see a few chips; MAX8900A, MCP73831, TP4056, AND HX3589 chips available. However, I only see a breakout board for the MAX8900A…
I’d LOVE to do it from scratch again, I need the charge specs for Lithium Ion cells though. I forgot them (3.7V max, forgot base voltage, etc). If I could I’d like to just write a routine in a microcontroller with some voltage regulator circuit (we used a buck boost regulator) to charge them.
Anybody know of some good projects on the internet?
You can Use a buck converter (or buck-boost if needed) controlled via PWM to regulate voltage and current.
You can sense voltage with an ADC and adjust duty cycle accordingly.
For Current sensing, use a current sensor like INA219.
Add an NTC thermistor to prevent charging in unsafe conditions.
There should be MOSFET-based switching to stop charging when complete.
Kudos for doing it from scratch but don’t feel like you have to. Maybe in 1992 but lithium batts and charging ICs were very mature by 2012. The first Ipod was introduced in 2001 and put lithium in everyone’s pockets. The Tesla Factory opened in 2010 and, by 2013, shoddy hoverboards were exploding in people’s living rooms.
I’ve bought some stuff from these guys, they’re fun and have some literature put together to help your research:
AWESOME thanks! It’s bringing back my old project. I think we charged at 4.2V. All our cells were in parallels and we used one voltage source to charge them. Before charging though I had to write a routine to balance the cells. We’d dump excess voltage across a resistor bank. Always thought it would be fun to do some more battery work like that.
Thanks for the tips! I’m currently fiddling around designing a boom box and I want it to run on 18650 batteries.
From what I recall implementing the charge process was somewhat straight forward when I built the charge controller back in 2012. I think it may use a bit too much IO on a microcontroller for my current project though.
I ordered a few TP5000 breakout boards. I chose the TP5000 cause it says it can charge at 2 amps per chip. Was really interested in one of the microchip chips. It’s SUPER small but could only do 500mA.