are you sure each one powers 4 drives and not just a big backplane with multiple sources for input?(Like the dual 8 pins not needed for power on boards that have them) have you tried powering it up as is for a test to see if the drives get power
Drives shouldnt be that much
“The Hdd: +5V 0.72A, +12V 0.52A, Barracuda 1TB, 7200.12”
What drives do you have? I know SAS high rpm drives use more power then that example above.
" How many HDD’s off 1 Molex? PICOPSU
Four drives should be fine.
The maximum current rating for the standard " Molex " drive power connector is 11 amps per pin. So you can get, as far as the connector is concerned, 11A at 5 volts and 11A at 12 volts. These are “returned” through the ground pins, so you don’t get 11 more A through each ground pin! The current you return through the ground pins is the same current you got from the + pins.
The +5 usage of a hard drive will be well under half an amp, so we can ignore that.
Most hard drives pull from 2 to 2.5 amps on the 12 volt line for a few seconds when they spinup, so four drives could get you to 10 amps. If this was a continuous draw I would say this was too much, because that “11 amps per pin” is for a 30 degrees C rise above ambient at the connector. 30C is almost 54F. That’s a lot! If ambient is 70F that means the +12 pins would be heated to 124F. Not good.
That would make me very uncomfortable if it was a continuous draw, but it isn’t – it only lasts as long as spinup takes. What’s the continuous draw? For some reason both Seagate and WD have gone to rating continuous operation in watts, not amps. The typical consumer drives are 8 watts or less, which at 12 volts is less than an amp (again, we’re ignoring the draw on the 5 volt line, as it is negligible). With four drives you’d still be under four amps, less than half the connector’s ampacity.
So four drives should be fine. I wouldn’t try for more, though.
If your motherboard or controller can be set to sequence the startup of your drives, so much the better.
Seagate desktop drive specs: http://www.seagate.com/www-content/product-content/desktop-hdd-fam/en-us/docs/desktop-hdd-ds1770-5-1409us.pdf
WD specs for their “Green” drives: http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-800026.pdf