Best Method for Power Cycles

M

maximus

Member
There are two ways I can power cycle a drive. The first method is to use a computer power supply to directly power the drive, and to use a relay to turn the power supply off and on the same way a computer would do. The second method is to wire two relays into the 5v and 12v wires to the drive, one relay for each wire.

The first method seems better to me for a few reasons. First it only uses one relay, leaving the other of a two relay board for IDE hard resets. Second, it uses the natural cycling of a computer power supply which in theory should be easy on the drive. And it is just much easier to wire.

The second method requires two relays which means I would have to use a 4 relay board that requires a 12v power source. That is not a big deal but it is more work and complicates things. It also leaves an extra possible point of failure of relay contacts in line with the power of the drive. This should not normally be an issue, but it is always a possibility and could make a good drive have issues and be hard to troubleshoot. With the first method a relay contact issue would be obvious in the fact that the power supply would not turn on consistently. Controlling the drive directly through relays can also be "dirty", meaning there is a small arc when the relays break and make contact. While I don't see this as an issue, it is still not as gentle as method one and has the potential to cause an issue.

So does the first method of controlling a computer power supply seem the best?
 
Jared

Jared

Administrator
Staff member
It wouldn't need to be two relays for a drive, just a double pole relay. And I don't think it'd really matter which way you did it, though I'm guessing the cost would be less switching low voltage rather than switching high voltage and you'd get a longer life out of the contacts. Just based on what other tools like PC-3000, DDI, & MRT do, I think switching the 5V & 12V is the way to go.
 
M

maximus

Member
At this time I only have the ability to control a limited number of relay boards, and the relays are all single pole double throw, so it takes two relays to do the 5v and 12v. And what I did not mention is that it will take extra modification of the power supply wiring to achieve this (cutting and soldering wires as the SATA and MOLEX connectors are on separate wires). Remember, I am not building my hardware from scratch for this. And as for contact life due to voltage, I am not planning on controlling the high voltage input of the power supply, but using the power-on wire to turn the supply on and off like a computer does (5v very low current).
 
M

maximus

Member
jol":2zuwgk5h said:
[post]4028[/post] you might use only 1 relay for the GRD
Click to expand...
That sounds great in theory. But what if the user has the drive touching a metal part of the computer or the power supply? That could easily create another ground path, and not a very good one either. I will not use a relay on the ground as too many things could go wrong.
 
M

maximus

Member
I have thought of a fatal flaw with my idea to use a separate actual computer power supply as the power source, which can be summed up in the phrase "potential ground loop". :(

So my next question is: Do any of the professional tools supply the 3.3v for SATA drives? I have read that almost all (if not all) regular SATA hard drives do not use the 3.3v, and that only some newer 1.8" SSD drives require it. This will make a difference in how I approach this. Not needing the 3.3v will make things much easier for me. I could use a simple Molex power adapter like what comes with USB drive adapters, as that would not cause a ground loop since it is not grounded. And actually there does exist a cable that goes from Molex to SATA with 5v to 3.3v converter made to power those drives, although it lacks the 12v.
 
Jared

Jared

Administrator
Staff member
I don't know that the 3.3 is necessary, not used that I'm aware of on most drives. Switching ground is definitely a bad idea, especially given that the entire aluminum housing is one big ground and some guys (myself included) work on an esd protected bench which is essentially one big ground path.

Perhaps something like this would be the solution you're looking for: http://www.amazon.com/SainSmart-Eight-C ... B0093Y89DE
 
M

maximus

Member
Jared":2jnvgx1w said:
Perhaps something like this would be the solution you're looking for: http://www.amazon.com/SainSmart-Eight-C ... B0093Y89DE
Click to expand...
There are 4 different versions of that: 1, 2, 4, and 8 relay board. The 1 and 2 relay boards are 5v and fully USB driven (I have two of the 2 relay boards). But the 4 and 8 relay boards require a 12v power supply to run them. What I need to do is figure out what I need to accomplish and how to do it with either version.
 
M

maximus

Member
I was thinking that those small power adapters that come with many of the USB to SATA/IDE adapters would be a good choice, but alas, they do not seem to have very stable voltages. So it looks like the power will come from the computer being used. That is the only safe way. So I will take both molex and sata power extension cables and run them through the relay board so there are both options on both ends. That still leaves the possibility of someone using an external power supply if they need, as long as they understand the risks.
 
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