FAQ
TL;DR: A 3.5-inch SATA HDD can work over a USB–SATA cable, but it needs external power; “+12 only on the three right pins.” Include +12 V and GND, not 3.3 V. [Elektroda, icosie, post #16970375]
Why it matters: This prevents non‑spinning drives and protects your USB port from wiring mistakes for quick data recovery.
This FAQ is for DIY users asking how to connect 3.5-inch SATA 2/3 HDDs using USB adapters and separate power supplies.
Quick Facts
- 3.5-inch SATA HDDs require external +12 V power; USB 5 V alone won’t spin them. [Elektroda, Freddy, post #16970653]
- Many 3.5-inch HDDs do not use 3.3 V at all. [Elektroda, Freddy, post #16970631]
- +12 V appears on three rightmost SATA power pins; the next pin is GND/delayed start. [Elektroda, icosie, post #16970375]
- SATA is backward compatible (newer drives work at older host speeds), but not upward. [Elektroda, Freddy, post #15874238]
- “7+15 pin” means 7 data pins + 15 power pins on standard SATA connectors. [Elektroda, bicik4096, post #15874150]
Will a 3.5-inch SATA 2/3 drive work with a simple USB–SATA cable?
Yes, if you add external power. Use the USB–SATA cable for data and supply +12 V and GND to the drive’s SATA power connector. Without +12 V, a 3.5-inch HDD will not spin up. “I have been using this connection for over a year,” notes one user. [Elektroda, Freddy, post #16970653]
Does a 2.5-inch “7+15 pin” USB–SATA adapter physically fit a 3.5-inch HDD?
Yes. The wide SATA plug is the same style and fits both 2.5-inch and 3.5-inch SATA drives. Just remember that 3.5-inch models still need separate power. “This wide plug has to fit into the slots on the drive.” [Elektroda, ryszard1955, post #15873345]
Do I need a separate power supply for a 3.5-inch SATA drive over USB?
Yes. Provide +12 V and GND to the SATA power connector. USB’s 5 V is not enough to spin 3.5-inch drives. Users report reliable operation when powering only the +12 V rail externally while the USB cable handles data. [Elektroda, Freddy, post #16970653]
Is 3.3 V required for 3.5-inch SATA HDDs?
No. “3.3 V voltage is not used in 3.5" drives.” You only need +12 V (and GND) for spindle and electronics. This simplifies wiring when using a bench PSU or a PC power supply. [Elektroda, Freddy, post #16970631]
Which SATA power pins carry +12 V and ground?
+12 V is on the three rightmost pins of the SATA power block when viewed from the plug end. The next pin is GND/delayed start support. Quote: “+12 only on the three right pins.” Triple‑check orientation before applying power. [Elektroda, icosie, post #16970375]
What happens if I wire −12 V or skip ground by mistake?
The drive won’t spin and you risk damage. One user saw no spin after incorrect wiring. The correction was simple: connect GND and +12 V only. “You are to connect the ground (GND) and +12 V.” [Elektroda, Freddy, post #16970725]
Are SATA I, II, and III devices compatible with each other?
Yes, with downward compatibility. A SATA III drive negotiates down to SATA II or I speeds on older hosts, but not up. Quote: “Yes, but only down.” Plan for reduced throughput when mixing generations. [Elektroda, Freddy, post #15874238]
Is it safe to feed 5 V from a PSU while also plugging the USB cable into a laptop?
Use caution. One user powered +5 V from Molex and hesitated to connect USB, worrying about backfeeding the laptop port. The thread does not confirm safety. Avoid connecting until you isolate the USB 5 V line or use a data‑only cable. [Elektroda, dell44, post #16978649]
How do I power a 3.5-inch HDD with a USB–SATA adapter (3 steps)?
- Connect the USB–SATA cable to the drive’s data+power shell for data.
- From a PSU, wire +12 V to the three rightmost SATA power pins and connect GND to ground pins.
- Verify polarity and pin alignment; then apply power and plug in USB.
[Elektroda, icosie, post #16970375]
Will this setup work with a phone via OTG?
It can enumerate if the drive has proper external power. A user reported the phone detected the drive once +12 V/5 V power was provided externally. File access then depends on the phone’s OTG and filesystem support. [Elektroda, dell44, post #16978649]
Can I use the same USB–SATA cable for 2.5-inch drives?
Yes. The 7+15 SATA connector fits both sizes. The forum user confirms the wide plug fits and works across drives. For 2.5-inch HDD/SSD, power needs differ by model, but the connector is identical. [Elektroda, ryszard1955, post #15873345]
What does “7+15 pin” mean on the adapter listing?
It describes standard SATA connectors: 7 pins for data plus 15 pins for power in one shell. The thread starter referenced a “USB HDD 7 + 15 pin 2.5" SATA” cable while asking about 3.5-inch use. [Elektroda, bicik4096, post #15874150]
Can I power the drive from a PC PSU’s Molex connector?
Yes, many users do. One participant proposed feeding the missing voltages from a computer PSU Molex while using a SATA–USB bridge for data. Ensure you deliver +12 V and GND on the correct SATA power pins. [Elektroda, dell44, post #16970309]
Why didn’t my drive spin after I connected power?
Check for wiring errors. A user initially used the wrong voltage and saw no spin. The fix: connect only +12 V and GND to the SATA power pins, then try again. This resolved the issue. [Elektroda, Freddy, post #16970725]
Can you connect a 3.5-inch drive to such an adapter, will it start correctly? I want to buy more of them in one go, so I want to be sure.
The plug fits but the 3.5 "drive will not move, it needs additional 12v and 3.3v
