I wanted to make a battery charger for my car, because I have this car that I rarely use, and one day when I want to start it, the battery might be flat.
Talking about the cheap side, the market has basically two types of models. One “Smart”, switch mode power supply with a bit of electronics, and another “Dumb” charger, just a transformer and a bridge rectifier.
The Smart charger is good and fairly underpowered. Sometimes it does too much analysis of the battery and refuses to charge it, for reasons unknown to men; or sometimes it starts charging and stops abruptly.
The Dumb charger, charges, no matter what, but the cheap ones are so bad, it’s an insult to the consumer. They are SO underpowered, so poorly made, if it wasn’t so tragic, it would be laughable.
I wanted put my charger to the battery, and connect it to a programmable power socket, to periodically come to life and charge my battery. The Smart ones cannot do that, because when they’re powered up, you always need to press some buttons.
It’s simple and reliable, but I also added some safety features.
So, I started from the simplest design,
and added a few more components for safety and convenience.
The charging curve looks like this
And the final product works perfectly.
You can see how it all came to be in this video: