Ryobi Adapter

They sell these, but they're underpowered. I'm going to build mine at 20V, that's what the 18V battery measures when it's charged.

I'll start with a 24V transformer. I found a MC33167 that might get it down to 20V (rate 5A). LT1270ACT is rated at 10A

this guy used 20 amps. I found this on Amazon, which seems like it would work pretty well.

Deep Cycle

The other option I'm considering is a deep cycle battery. The catch is that I can't get one near 20v, so I need a boost converter. But I can just double the voltage. The deep cycle battery would probably be around $25.

http://www.electroschematics.com/648/555-voltage-doubler/

http://www.circuitsgallery.com/2013/04/automatic-battery-charger-controller.html

Transistors need to be TO-3 packages.

• Battery $25
• NPN power transistor $2.50
• PNP power transistor $2.50
• Heatsink $3
• Caps $3.75

I'm also going to get the etching supplies, makes more sense to buy in moderate bulk

• Boards: $12.50
• Ferric Chloride: $11