BC250-Power Adapter

BC-250 J2000/J2001 Power Adapter

A simple PCB that adapts the BC-250's J2000 and J2001 power ports to standard PSU cables. One side has two Micro-Fit connectors that plug into the board, the other side has a PCIe 8-pin (GPU cable) and an EPS 8-pin (CPU cable) header for your PSU cables. No components, just copper connecting one side to the other.

KiCad project files are in this repo.

⚠️ Warnings

• Use a single-rail PSU (or one with bridged rails) if you power the board from more than one connector. That means both headers on this adapter, or this adapter plus the board's own GPU connector (J1000). Two independent rails tied together will trip over-current protection at best, damage the PSU at worst. Multi-rail server and mining PSUs are the usual culprits.

Parts

Pick one option. Both include the two Micro-Fit connectors for the BC-250 side.

Option 1: Keyed (preferred)

Parts: $13.48 + shipping from both DigiKey ($4.99) and ModDIY ($9.99) = ~$28.50 total

Keyed connectors physically block the wrong cable type. Molex doesn't sell these to individuals, so buy them from a trusted reseller like ModDIY.

Option 2: Single DigiKey order (cheaper, some caveats)

Parts: $11.20 + DigiKey shipping ($4.99) = ~$16.20 total

Heads up: the 0039301080 only accepts a CPU (EPS) cable as-is. Its keying matches EPS housings, but GPU cables have a different key pattern (a plastic bridge between the pin rows) and won't seat. Tested and confirmed. For the GPU header you have three choices:

1. Buy the ModDIY PCIe header from Option 1 for that position (adds ModDIY shipping, so most of the savings disappear)
2. Trim the keying off a 0039301080 with a hobby knife. The shroud is nylon and cuts easily; take off less than you think, test-fit as you go, and don't nick the pins or the latch wall. A trimmed header accepts both cable types, so the warning below applies in full. Do this at your own risk.
3. AliExpress GPU headers like these exist and can work, but aren't recommended (unknown terminal quality on a high-current part). If you go this route anyway, get the GPU-8Pin-RA variant, NOT the GPU-8Pin-RA-Reversed one.

⚠️ Never plug a CPU cable into the GPU header or the other way around. PCIe and EPS pinouts are mirrored, so the wrong cable puts 12V where ground should be. This can kill the board and the PSU. The keyed connectors in Option 1 physically block the wrong cable. A trimmed header blocks nothing, so label your headers and double check before powering on.

Pinout (BC-250 side)

From mothenjoyer69/bc250-documentation:

        J2000                    J2001
     v                        v
[ LED1  12V   12V   12V ]  [ 12V   12V   12V   GND ]
[ LED2  GND   GND   GND ]  [ GND   GND   GND   PGD ]

LED1 and LED2 are broken out as labeled headers on this adapter. They're logic outputs, not a power source. To add a status LED, wire it from the pin to 12V through a resistor, cathode toward the pin. Drive strength isn't documented, so size the resistor conservatively.

Power

BC-250 side: Micro-Fit contacts are rated 5A each. Three 12V pins per connector gives 6 x 5A x 12V = 360W across both.

PSU side:

Plan around the safe numbers. The max figures are raw pin ratings with zero margin.

Check your cable gauge. The ratings above assume decent wire. 16 AWG handles the full connector rating, 18 AWG has melted on this board under sustained load, and 20 AWG (common on cheap or SFF cables) is only good for roughly half the rated current per wire. This adapter exists partly for that reason: splitting the load across both a GPU and a CPU cable keeps the current per wire low enough that even thin cables stay safe.

What the BC-250 actually draws:

One EPS header alone is tight even at stock, since gaming can peak past its 235W rating. Use both headers for anything overclocked or under sustained load. Together they're good for ~385W, which covers everything the board can realistically pull.

PSU sizing from the community: 250W+ on the 12V rail before overclocking, 300W+ for heavy overclocks, 400-500W+ for sustained full-CU compute.

Disclaimer

Based on community reverse engineering, not official schematics. Verify pinouts against your own board before applying power. Use at your own risk.