There's a free license version of Eagle Cad for viewing/printing/exporting gerbers etc.

Otherwise in the gallery you'll see a schematic and a layout guide.

The FETs and the Snubber Schottky are laid out along the edge of the PCB for direct mounting to the 3/8" x 3" x 6" plate heat sink. The other schottky requires a bolt on heat sink, nothing excessive.

A 120VAC , 120mm fan delivers around 80CFM blown across the FET heat sink (and the capacitors which are bottom mounted) . The PCB is then edge mounted vertically on the Alum. plate, aligned along the middle of the fan for double sided PCB cooling.

Use 6-32 mounting hardware for the FETs and a 4-40/ insulating kit for the TO220 snubber rectifier. The 2200uF cap associated with the snubber gets quite hot so ensure proper airflow. All electrolytic caps are Low ESR 105°C types. Use quality caps like Nichicon, Rubycon, United Chemicon etc. Caps under 30 milliohms ESR should be ok.

If you look at the layout image you'll see crosshatching along the red top copper layer...this is the solder mask stop to allow heavy solder thickening of the traces to carry heavy currents. Similarly, the bottom solder mask stop applies to the bottom traces so it's best to use the EagleCad layout which has all this done for you. I use 'used' 2.5mm solder braid to augment these traces, it works well.

The snubber employs a T-20 21W/5W dual filament Brake lamp which provides for reverse battery connection while permitting up to 26W of continuous snubbing. The lamp also glows according to the kick back energy. Brighter = more energy that the battery is absorbing and the more energy created by the collapsing magnetic field of the battery and cabling. This means the battery's impedance is improving- a visual cue..

This snubber is important to keep the FETs from avalanching outside their SOA and eventually failing.

The leads on this lamp must be properly cleaned and tinned, it is bottom mounted like the capacitors.

There is a SMD relay with an 18V zener monitoring the well being of the lamp via the associated capacitor's voltage. Once the capacitor exceeds 18V + 4.5V the 4.5V relay will pull and crowbar the main fuse. This protects the circuit from lamp failure.

The layout uses a custom SMT pad for the FETs rather than thru hole. Bend the FET Leads @ 90° from the wider part of their leads and trim this created L shaped lead to 1/8". Tack solder the FET gates to the PCB before aligning to the Aluminum plate and marking the center spots to drill the 6-32 mounting hardware. Also, solder one pin of the Schottky snubber onto the PCB and mark its 4-40 center hole. onto the alum plate.

Remove the AL Plate drill and tap it, then realign the PCB with the FETs and schottky, reflow the soldered joint to allow for flush strain relief mounting with the machine screws installed. Remove the screws and the plate and finish solder the semiconductors.

When building the two quad #12 AWG, OFC cables, crimp the 1/4" spade receptacles and solder them to the cables as well. Solder the other ends of the cables right up into the jaws of the crocodile (200A) clamps to minimize clamp losses. Keep these cables as short as is feasible, perhaps 2' each.

more details and pics to come...