I’ve got a PC-based product that normally shows volt-amp draws, reported by the UPS, in the 65-130 range.
Someone is alleging that by adding 3 hard drives (500 GB Seagate/Maxtor 7200 RPM models) that the 400W power supply it ships with will be overtaxed, and hard drives may fail to properly spin up.
Is this vaguely feasible, at all?
Also, what’s the peak amperage I can expect from these drives?
It’s not remotely feasible. To overtax a 400W power supply you’d need a screaming dual-graphics card setup and then figure out a way to pin both gpu’s and the cpu simultaneously. IIRC hard drives pull 10-20W. Check the specifications for the specific model you’re getting.
Some specs from Seagate:
Their “Barracuda LP” (low power) drives draw 2 amps of 12 volt at startup, but operater at an average of around 6 watts and idle at 3 watts for the 1 TB model (the smallest in that line)
A 500 GB 7200.11 drive is rated for a 3 amp startup load. No further details are easily found, but you can probably be safe in estimating that it would draw around 5 watts at idle and 10 watts while active.
Three of those would pull 9 amps or 108 watts to spin up. Add that to the 130 watts for the rest of the device, and you’re under 250 watts, so I can’t envision a 400 watt power supply being unable to handle that.
And now for some power supply specs as it just hit me that computer power supplies may be labeled as “400 watts” but that’s an aggregate of 5 volts and 12 volts and some assorted others.
A 420 watt “Silencer” from PC Power & Cooling jams out a continuous capacity of 20 amps of +5 and 30 amps of +12. Your three drives will pull only a third of that available 12 volt power, and for only a quarter-second or so.
Vantec’s 400 watt “Ion” puts out 40 amps of +5 and 16 amps of +12 at a 60-second peak load.
I’d expect a 400 watt PSU from anyone else would put out similar amounts of juice.
Another vote for “not a problem”. Some motherboards support staged spin-up of the system HDs if you’re at all worried about it.
I don’t think you’d need quite that much of a rig to overtax a 400 W PSU, especially on the 12 V rail if the PSU isn’t designed right. On my “wishlist” to replace my four year old desktop (which probably isn’t going to happen any time soon, but I digress), I have mid-high range parts with a single-GPU single-graphics card setup, and I decided that 500 W was about right for that system. Hell, I think the PSU in my current desktop is a 500 W, and it isn’t going to win any awards.
Then again, I think that a quality PSU is the most important part if you’re concerned about stability and longevity, so I might have a tendency to be overly generous with the power rating. But I think overtaxing a 400 W is feasible for midrange gaming systems, depending on the specific components.
To answer the OP, first, hard drives are not, by themselves, a big power draw. Second, hard drives not spinning up isn’t generally a symptom of an overtaxed PSU; you’d be more likely to run into serious stability problems under heavy load rather than flaky hard drives at boot. Third, 400 W will be just fine for anything that isn’t a gaming/hobbyist system.
Just for kicks, specs:
CPU:
Intel Pentium 4 CPU 3.00GHz
RAM:
512 MB
Video:
Intel 82945G Express
HDD:
Quantity 1-4 of Seagate ST3500630NS
Optical:
Lite-On CD R LH52R1P
Video Input:
Quantity 2 of Sensoray 617 [ http://www.sensoray.com/products/617data.htm ]
Serial Input:
Moxa CP-114 [ http://www.moxa.com/product/CP-114.htm ]