This is my attempt to solve the problem of USB "vampire power". This occurs when joining two USB devices who both have their +5v rails present on the USB connector. The result is that if only one of the two devices is powered on, it will try to power the other device via the USB.

The most common example is when connecting an OctoPi server to your 3D printer. If the Octopi remains on and you power off the printer, its display and fans will remain running, as they are being powered by the Pi's USB. This is an unhealthy situation, as the Pi does not have enough current capacity on the USB to power your printer, nor does it have the additional 12v or 24v required by the steppers and heaters. The eventual end result, even if the printer remains idle, is a baked Pi.

My project applies a bit of garlic (to chase away the vampire, of course!) by interrupting the USB 5V pin and only allowing the ground and signal pins to pass through. My original thought was to modify the USB cable, but this separate coupler provides a more flexible and less destructive solution.

The only parts needed are two right-angle PCB mount USB A female connectors, three short pieces of wire, and a bit of solder, plus the printed case.

I started by carefully bending the G, D+ and D- pins of each connector so that the stick out flat, away from the body of the connector, taking care that the bend does not cause the pins to short against the connector's metal shell. I then cut off the 5V pins on both connectors, and wired the correstponding pins of each connector together. The printed case separates the two connectors by 10mm, so choose the wire lengths to allow this spacing in the assembled adapter.

Once wired up, the completed assembly should slide easily into the body. Notice that there are holes in the body to accommodate the two mounting tabs on each connector, which also help to keep each connector positioned correctly in the case when plugging and unplugging.

The lid is attached to the case body by four M2 x 6 self-tapping screws.

PLA is more than adequate for this project, and it was printed with a 0.4mm nozzle at 0.2mm layer height, using a profile that's optimized for speed rather than beauty. No supports are required.

I am currently using this adapter to run my Ender 3 V2 Neo with Octopi running on a Pi Zero 2 W. Two 0.25m right angle Micro USB to USB A cables complete the connection between this adapter and the Pi and Printer, and no longer have any problems with vampire power!

Creality

Ender-3 v2

No

No

0.2mm

10%

Refer to pictures for assembly.

Designed using OpenSCAD, sliced using Cura 5.4