I’d started building this a couple years ago and hadn’t finished the project until recently. It’s basically a high amperage battery charger with a small foot print, lot’s easier to move around than your run of the mill big box chargers. The primary side of the transformer is tapped for 5 charging rates from around 6v thru 15v + @ up to 30+ amps. I also added a carbon pile that can be used to load test the battery you’re working on if need be. The primary windings are relay switched and can only be energized with load from the carbon pile out of the circuit. In addition reverse polarity diodes are used on the output to prevent damage if the leads are reversed. The output is shunted for a panel mounted ammeter to be added later and it’s all mounted in a 16″x16″x6″ Wiegmann inclosure with 2 side mounted cooling fans.