Fix power switch cable connector size and placement

[dkonigsberg]

The power board (Rev C) currently uses a Molex 768290002 Mega-Fit 5.7mm pitch connector, combined with a Molex 451360201 cable assembly (cut in half, with QC connectors crimped on) as a way of attaching the power switch.

In the current revision of the board, this arrangement has the following problems:

• With the plug and wire hardness connected, the whole thing is rather tall
• This height slightly invades the area where the main board overlaps inside the enclosure, causing fit issues
• The wires on the cable assembly are quite stiff, and also too thick (12AWG) to actually fit the current choice of QC connectors (which only hold up to 14AWG).

This absolutely needs to be fixed, sooner rather than later, The current proposed approach towards fixing the issue is as follows:

• Draw a reference line on the power PCB layout that's offset >25mm from the interior edge of the board, marking the location where the main board will overlap it inside the enclosure
• Adjust the position of the power switch connector so that it does not cross this line
• Review available connector choices to see if there's anything smaller and/or shorter, which offers better fitting and more flexible wires. (stiff wires can cause undesired side force on the QC connectors)

The main challenge with smaller and/or more reasonable connectors is simply that the pins are closer together than we'd like for trace clearance. As such, extra layout/routing care may be necessary.

[dkonigsberg]

One simple solution would be to not use the noted cable assembly, which uses 12AWG wires, and instead simply buy the components to make a 16AWG assembly:

• Pre-crimped lead: 797582037
• Crimp socket (plug): 1700010102

A bit challenge with selecting any options is wanting sufficient clearance between the pins, and being able to find pre-crimped leads that match the system.

[dkonigsberg]

The other solution, now likely for the next revision, is to change to a smaller connector. The Molex Mega-Fit stack puts the top of the plug 28.8mm above the PCB, plus whatever space the cable bend takes.

The alternative now being considered is the Molex Mini-Fit Jr series. With this connector, the stack puts the top of the plug only 23.5mm above the PCB (plus cable bend). While only a ~5mm difference, when combined with the ease of repositioning a smaller connector, this should be more than enough. The only downside is that the lowest common rating of the Mini-Fit components is only 9A per contact. However, we're fusing at 5-6A, so that should be fine. Will still stick to 16 AWG wires, for better flexibility.