My son handed me a 10 year old external drive enclosure, "Dad this isn't working". A quick look makes me think that the original power supply has been lost. It came back to me with a USB Type A to barrel connector power cable plugged in. Which supplied enough power (when connected to an Apple 5V 1A DC wall wart) to light the front indicator LED but not spin the exhaust fan or power the drive system.

My question is regarding a good protocol to follow to determine the characteristics of a replacement power supply. Obviously I want to avoid releasing smoke if I can.

The unit is labelled as an OWC Mercury Elite-AL Pro, there does not seem to be any reference material for it any more, however it is similar to a current model

The rear panel has no power specs printed on it. Nor does any other internal or external surface of the unit (the only sticker is an internal RAID jumper switch configuration guide).Rear Panel

The RAID controller board seemed in good condition on inspection, again no power information visible. No luck googling the identifying numbers.PCB front PCB back

I noticed two power regulators on the PCB, one on the front and one on the back. They are labelled L353 G117 (front) which I think could be one of these. On the back is 1117-18 09234D1 which I think could be one of these.

The drives are dual Seagate barracuda 7200.10 (ST3500630AS) which need 12V 0.52A and 5V 0.72A, which matches what I know about the molex power connector. Drives

My best guess is that the power supply needs DC 12V 1.5A. I was thinking I'd use a bench power supply to slowly crank up the voltage from 5V to 12V (with the current limited at 1A) and then slowly up the available current to 1.5A. Is this a reasonable plan?

  • 1
    \$\begingroup\$ The 3.5" drives, memory serving, require 12 V (motor) and also 5 V (logic) and I think the SATA ones (many) also require a separate 3.3 V (logic, again.) The 12 V for the motor might be fine coming directly from the external supply. I don't think it has to be a precision value. But you do need 12 V. So if there isn't a regulator for it, then you may be right about the voltage for the external supply. And yes, you seem to be doing a yeoman's job working out the likely current, too. You brought me along with you and I think you have a good shot at this. +1 for the question, of course. \$\endgroup\$
    – jonk
    Sep 9, 2021 at 3:32
  • \$\begingroup\$ Hard drives need 12V. What about the fan, does it say 12V on it? \$\endgroup\$
    – Justme
    Sep 9, 2021 at 4:11
  • \$\begingroup\$ @Justme, yes I took the cover of the fan just now to check 12V 0.12A (Evercool EC4010TH12E). Looks like 12V is the go. \$\endgroup\$
    – RowanP
    Sep 9, 2021 at 4:39
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    \$\begingroup\$ After all the detective work, and assuring me this morning that no such thing existed on the planet, my teenage son came and handed me a 12V 4A supply and said, "Found it". Kids. \$\endgroup\$
    – RowanP
    Sep 9, 2021 at 4:56
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    \$\begingroup\$ @RowanP Cool!! So now you know. I had been thinking that 1.5 A was a bit low. But just the same I enjoyed your thinking process. It was good. The 4 A spec is more in the territory I was thinking more likely. But still, that's higher than I imagined. Glad to see that you have it solved!! And you have a good head for things. Best wishes! \$\endgroup\$
    – jonk
    Sep 9, 2021 at 10:08

1 Answer 1


It's sort of reasonable. But I wouldn't do it, and I wouldn't do it with drives connected, and I wouldn't do it without the drives connected.

Depending on how it's built, the input stage can overheat and burn out if the input power is too low. To get the required secondary voltage, it runs at 100%, which it's not designed to do. And the drives don't work properly at low voltage / low current either.

A typical single supply is 12V 2Amp, and that the replacement model double supply is 4A. That's what you should be looking for. What you can check before you plug it in, is that the open circuit supply voltage isn't too high. If it's above 12.5, you should check the supply connnected to a dummy 500mA load, to see that it comes down to a reasonable value, and with a 4A load, to see that it doesn't sag too badly.


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