PSU - Max Drives on Single Cable?

[Lurick]

So I recently got a new server case and the backplane uses molex plugs, 1 for each drive, for a total of 16 molex plugs.

I've got a Seasonic Focus PX-850 and several sata power to 2x molex splitters. My question is how should I divide everything up?

 

Would it be safe to take one PSU cable with 4x sata power plugs and connect the splitters so 8x drives are powered off a single cable?

Or should I adjust things so only 6 drives are powered off the 4x sata plugs?

[mariushm]

Your limitation is the headers on the power supply (if it's modular psu), where each pin is rated for at least 9A ...  if it's not modular, it's the actual cables which can do around 10-14A without small enough voltage drop due to wire resistance

 

The headers have a single 12v and a single 5v wire. 

 

A classical hard drive will pull around 1A from 12v and maybe 0.6A .. 0.75A from 5v , but will pull maybe 2A for a short period (a few seconds) when the drive starts and spins up the motor.

 

A SSD uses no 12v, but uses 5v instead. When idle and reading files, it's mostly low power, typically under 1w (0.2-0.5A on 5v) , but when writing A LOT of data, the power consumption could go up to 8-10 watts (2A on 5v)

 

So it would best to not use more than 4 SATA or molex connectors on a single chain of connectors. It would be safe to use all four on a chain, but if you can, would probably be better to use only 3 per chain.

 

 

[mMontana]

Any HDD and SATA SSD provide datasheet with power consumption.

This is the side label of your PSU (sort of)

(source)

And 70A is an hefty power budget.

These are the cables for this PSU. The 1 at the left means that you have that provided with it.

As a rule of thumb, for drives for any cable I'd use only 1 splitter, to the closest connector possible to the PSU, if all the connectors are available.

On a 4 port cable, can increase up to 20% the amperage.

If a port is not used, using a splitter wil strain the power cable as much as having all ports connected. However... more resistance due to splitter. In long terms (more than 3 years) a 6 months checkup on oxidation might be a good idea. 

 

[Lurick]

@mariushm@mMontana

Thank you both for the help however it turns out this is a non issue -.-

The case in question:

http://www.istarusa.com/en/istarusa/products.php?model=M-4160-ATX

Was bought from Newegg where they do NOT mention that there are 4 molex per backplane for REDUNDANCY (it's only called out in the notes on the site) when using their redundant PSU setup. You only need TWO per backplane by default when running a normal PSU. They also didn't include a manual with the case which is dumb too.