Hi, all. My first post and it's "unusual". But I'd rather embarrass myself asking obtuse questions than accidentally burn up the drive in question.

1. I have an older SATA drive with a 4-wire Molex power connector.
2. I want to mount it internally, as a second drive that will usually not be powered on.
3. My plan (unless you say otherwise) is to spice a Single pole, single throw switch (SPST) into one of the four Molex wires so I can interrupt electrical current to the drive.
4. Just flip the switch to ON for accessing the drive, and OFF most of the time.

QUESTION A
Assuming this can be done without damaging the drive, can you tell me with certainty which wire should receive the ON/OFF switch. The following is my understanding of the pin/wire assignments:

Pin 1 YELLOW +12 V
Pin 2 BLACK Ground
Pin 3 BLACK Ground
Pin 4 RED + 5 V

Would cut the YELLOW wire, or the RED, or...?

QUESTION B
18 gauge (AWG) seems to be the standard. I may find it necessary to add wire length. Must I use only 18 gauge wire, or would heavier (or lighter) gauge work?

QUESTION C
Will I be able to throw the switch while the system is powered ON? Or should I only throw the HDD power switch when the system is powered OFF/DOWN?

Thanks

If this SATA drive is not connected to a Hot Plug SATA port - you definitely
need to power off the pc before turning on your hdd.

Hot Plug is usually only available on special defined (6G) SATA ports of
modern mainboards.

On Vista, Windows 7 + 8 you need to start with AHCI enabled in the
BIOS and apropriate drivers have to be installed (usually done auto-
matically - or is allready included in a pre-installed Windows-System).

For XP: AHCI drivers + Hot Plug works only when either drivers are
installed together ( F6 ) with XP - or afterwards in a running
( IDE compatible ) XP-system ( complicated !!! )

***
If above is solved or Hot Plug is not necessary (PC is switched off/on
before the additional drive is turned on) you could use a 5 1/4" hdd
bay with a 3,5" frame for 3,5" SATA hdd. Most of them have a key
- and when the drive is locked with the key its power is turned on.

Should not cost you more than $ 20,- + 1 power cable + 1 SATA cable
and avoids any cabeling and pin confusion.

+++

or Ext. USB

_________________
Kuwait Data Recovery - UNIX GTC
The only reason for time is so that everything doesn't happen at once. By: Albert Einstein

falther ==

Thank you for the in-depth reply. As I understand your comments, you are suggesting an external SATA drive bay - one that has a keyed ON/OFF switch. Per your suggestion, I searched Amazon.com but did not find one. I did find some internal hot-swap racks but they were not suitable - either very expensive, or looked as if they would add to drive heat build-up. If you have a link to the type of enclosure you are suggesting, I would like to see it - if only as a starting point for further searching.

Apologies. I failed to mention that the OS is Windows XPpro SP3 (this is my old/backup system). I have been struggling with USB 2.0 difficulties for a year with no resolution (6 USB 2.0 ports, but when I connect certain USB 2.0 devices, XP advises "This device can work faster if attached to a USB 2.0 port"...very frustrating).

I mention the USB issues because einstein9 suggested External USB. Thanks e9, but it appears USB is no longer stabile on this system.

Honestly, I would very much prefer to leave the drive mounted internally. At present, I leave the case side cover off and simply unplug the molex connector (with system OFF) to disable the drive. When I plug the molex back in (with system OFF) and boot the system, the drive is present.

It would be much more convenient to interrupt electrical current to the drive by way of a switch (and I worry that connecting/disconnecting the molex many times will eventually damage pins/connectors). So, can anyone advise me with absolute certainty? I would like to know which of the four molex wires should receive the switch.

Pin 1 YELLOW +12 V
Pin 2 BLACK Ground
Pin 3 BLACK Ground
Pin 4 RED + 5 V

Thanks

I found this Molex 4-pin power switch 12V DC on Amazon.com
http://www.amazon.com/Molex-Pin-Off-Power-Switch/dp/tech-data/B001Q5Q1KQ/ref=de_a_smtd

I think it is intended for case cooling fans. I've sent an email inquiry to the seller, but am not sure if he really knows whether this product is safe for use with a hard drive?

Do any of you know if this switch would be safe to use for powering a SATA hard drive ON and OFF only when the system is OFF?

This comment appears on the User Reviews page: "The item I got is different from what's pictured: it seems ground is switched rather than 12v so it might work with 5v equipment too. Your mileage may vary. "
http://www.amazon.com/Molex-Pin-Off-Power-Switch/product-reviews/B001Q5Q1KQ/ref=dp_top_cm_cr_acr_txt?ie=UTF8&showViewpoints=1 See comment #5, by Brandon Thomson on November 9, 2011

If you're going to be messing around with this stuff. I would connect/disconnect both the 5v and 12v lines when the power supply is switched off. That means a dual switch or two separate switches, used when the system is powered down completely. Not just soft-powered-down, but AC disconnect via hard power supply switch.

Don't go toggling the new HDD switches while the system is powered up either. As voltages transition it will stress the SATA lines. No good.

If you start switching off just the ground wires you're going to get all kinds -7v loops. That is not good either.

Any switch is "safe" as long as it is rated above the maximum current the load expected. That means looking at the HDD specs for spin-up surge current.

It is not likely the guy selling the switch will know the ratings, and he most certainly won't know the ratings of your HDD. Therefor he is not in a position to say whether it will work. If he does, then he is BS'ing you. You need to confirm the ratings yourself.

Good engineering practices and proper operation will make this a successful project that won't shorten the life of your major components.

_________________
On a clear disk you can seek forever.

Thanks, Keatah ==

I found specs for the hard drive (WD1600JS) at this URL:
http://wdc.custhelp.com/app/answers/detail/a_id/1340/~/specifications-for-the-160-gb-second-generation-serial-ata-drive-(model

There is a "Power Requirements" section, but no "spin-up surge current" information:
(Based on a 20% duty cycle) 12V Read/Write = 450 mA 9.5 W
(Based on a 20% duty cycle) 5V Read/Write = 800 mA 9.5 W

SWITCH terminology
Single pole, single throw (SPST): One physical switch thrown to connect/disconnect one pair of terminals. Transmits current to a single destination, such as a light bulb.
Double pole, single throw (DPST): One physical switch thrown to connect/disconnect two pairs of terminals in parallel. Transmits current to two destinations simultaneously, such as two light bulbs.

Per your advice, it appears I should install either two SPST switches (one for 12V wire and one for 5V wire) or a single DPST switch instead (which would avoid the possibility of accidentally switching 12V ON and 5V OFF )

I found this heavy-duty DPST switch on Amazon. It's rated for 20 amps @ 125V AC
http://www.amazon.com/Heavy-Duty-Toggle-Switch-DPST/dp/B006YXY9DG/ref=sr_1_2?ie=UTF8&qid=1357669013&sr=8-2&keywords=dpst+switch

Apparently AC ratings must be translated into DC terms according to comments on this web page:
http://forums.mikeholt.com/showthread.php?t=113222

I'm confused by this, but this excerpt from the page makes sense: b) "...switch contacts, relay contacts, contactor contacts and small circuit breaker contacts that are marked "AC only" can in fact be used on DC, but only at about 10% of the rated voltage."

The switch is rated for 120V AC. 10% of that would be 12V DC. I do not know how to interpret the drive's power specs, but IF the two wire loads must be summed (because a single switch is controlling both loads) the excerpt seems to suggest that the switch might not be sufficient...(I'm not sure if the two wire loads need to be added together...)

Watts / Amps = Volts

12V + 5V wattage / 12V + 5V amperage = total volts

9.5 + 9.5 W / 450 mA + 800mA = total volts

19W / 1.25A = 15.2 Volts (12.7% of rated AC voltage)

What do you guys think?