Recently, we’ve described a very sophisticated lead-acid battery charger in SILICON CHIP – in fact, perhaps one of the most sophisticated DIY designs in the world. But hey, it might be good but it also costs a lot more than a few dollars.

This design? Well, it’s right at the other end of the scale – the $2 trickle battery charger! Sure, it takes a bit of fiddling to initially set up but after that you’re laughing.

The components

This battery charger comprises just a plugpack, a resistor and a fuse.

For charging a 12V battery, a plugpack with a nominal rating of around 13-14V and a current cresiapacity of about one amp (1A) is fine. Low-cost plugpacks matching these specs can be found wherever consumer goods are being thrown away or being sold cheaply secondhand. Those with the required ratings were often used to power printers and older scanners.

Make sure when selecting the plugpack it has a DC (direct current) output. Some higher-powered plugpacks have an AC (alternating current) output as they’re designed for garden lights and so don’t need to rectify the AC to DC. The plugpack shown here was sourced from a shop at the local tip – half a dozen of them for $5.

A high-power resistor limits the charging current flow, especially when the battery is well down in voltage. Always be on the lookout for high power resistors - they're amongst the few individual electronic components always worth salvaging.

A 1A 13.5V plugpack makes an ideal foundation for a trickle battery charger. Plugpacks like this can be picked up for nearly nothing at the tip and where secondhand electrical goods are sold.

The resistor needs to be a high power design (eg, 5W) with a resistance around 5Ω. Lots of junked goods use high power resistors so always keep an eye out for these components – they’re amongst the few individual electronic components always worth collecting.

Chassis-mount fuseholders can be found in amplifiers and in-line fuseholders in the supply wiring to car radios and amplifiers. The fuses themselves? Well, they’re in nearly all goods – and like high power resistors, fuses are always worth salvaging, sorting and storing.