I'm using a wall adapter to power a Molex power supply, trying to connect it to an HDD via a Molex to SATA power adapter. The 12V rail seems fine, but the 5V rail is only reading 4.78V. None of my drives spin up when connected, and the PC doesn't recognize them at all. I've tested multiple Molex to SATA adapters and several different drives, but none of them respond. My question is: is 4.78V too low to power the controller board? Shouldn't the drives at least spin up with only the 12V rail, given that the motors are powered by it?
2 Answers
4.78V could be within a tolerable range, but it's best to measure it under load—meaning while something is connected. If these drives work fine in a standard setup, it’s very likely an issue with the USB adapter instead of the drives themselves. Double-checking that would be wise.
Some HDDs have different voltage requirements, and some might not use 12V at all for the motor. Check the power requirements on the drive’s label or online. It's important to see if your specific model needs additional voltage. If the 5V is low, it might not initialize the controller board properly. Keep in mind that not all drives behave the same way with these voltages.
From what I've researched, the motors indeed usually run on the 12V rail, while the controller circuit runs off the 5V. If your 12V is solid and the drives still don't spin, checking the Molex to SATA adapter is a good step.
Exactly what I'm thinking! I've just ordered a new SATA to USB adapter for testing. I remember reading that the motors should activate if they get the 12V, even if the controller isn't powered. Just trying to figure out what should ideally happen.