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Controlling 12V via a 5V signal

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New Member
Here's a simple project I've been brainstorming on...

I have a 3.5" external hard drive. The problem with it is that it doesn't spin down when the device it is attached to (via USB) is turned off.

I want to make the drive shut off when it no longer detects 5V on the USB's line.

The external drive enclosure has a manual rocker switch that cuts the 12V, 2A (from a wall-wart) to the HDD and some other power supplies (5V, 3.3V, 1.8V).

Can anyone recommend an SSR or other device I could use to switch the 12V line with the 5V from the USB?

The only limitation I have is space (only have about 1"x1").


New Member
Stupid question, is there not a setup utility that allows a "sleep" mode, rather than interfering with its power supply as this may cause damage the drive?


New Member
Unfortunately, no. From what I've been told, you can't find external enclosures for 3.5" drives that have auto-sleep features.

The device that the external drive is attached to won't spin down the hard drive. (It's not very smart.) The hard drive will keep whirring away, even when the device is powered off. The only way you can turn the drive off is by killing power to it.

I have the ability to inhibit the 5V line that supplies voltage to the USB-to-SATA controller chip as well as to the HDD itself. I don't know what would happen if I killed 5V and left 12V on the drive. I thought it would be safer to kill the 12V entirely, just like the power switch did.


New Member
Forum Supporter
Why not just use a simple 5V relay? Don't forget the diode across the coil.


Well i think its a good idea. I had a similar problem. I have 10 external HDDs for video backup and when powering down one day 1 of them didnt turn off. Came back the next day and it was red hot.
This idea would have saved me instead of nearly burning out the HDD.
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