I want to switch a hard disc drive on and off from it's power point with some transistors or mosfets. I know that it will depend from model to model but I was wondering about how much power I should expect it to draw from the 5v and 12v lines specifically. I know I can find power ratings but they don't say anything about what the division of power is between the two.

Alternatively even though there are two grounds, can I simply connect them together and just switch the ground? Or is there a reason they use two grounds?

Thanks.

 

This does not sound like a good idea as switching the power off of a HDD may lead to loss of data or damage to the drive. HDD power switching is controlled by software.

Timescope

 

I also had the similar idea that I want to assembly many HDDs, and then put them into the case of PC, and use the key from outside to control the HDDs which I want to use, but this should be make choice before press the start button of the PC.

You were care about the current of 12V and 5V, the two grounds must be used, because 12V and 5V had heavy load, you have to provide two current loop for them, otherwise the current may not enough.

I checked the current rating of HDD label, as 12V...50A, 5V...50A, but we still can't make sure how much current that we really needed, so we have to measure the current by our own.

Some multimeters provided 10A only, some provided to 20A, if you want to measure them more safely, then you have to make a power interface plug between the PC and HDD.

Normally plug:
4 pins female PC power plug → 4 pins male HDD power plug

Interface plug:
A PCB including : 4 pins male power plug, 4 pins terminals of Current meter(range 10A,20A), 4 pins female power plug

Adding Interface plug:
4 pins female PC power plug → PCB(4 pins male power plug, 4 pins terminals of Current meter (range 10A,20A), 4 pins female power plug) → 4 pins male HDD power plug


1. 4 pins female PC power plug.
2. PCB : 4 pins male power plug, 2 pins terminal of Current meter(range 10A,20A), 4 pins female power plug
3. 4 pins male HDD power plug.

You can measure anyone of 12V or 5V, and then measure the other one.

When you use the current meter, whatever then normal current meter or multimeter, you have to make sure the testing point is fixed and safety.