How many drives at PSU molex

[hawihoney]

I do use five drives in the following external case:

http://www.sansdigital.com/hddrack5.html

 

They are powered from this external PSU:

http://www.coolermaster.com/powersupply/b-series/b500/

 

The motherboard adapter of the PSU is connected to the external rack to power the single fan. Five drives are connected to the SATA cables.

 

Can I connect more drives to that PSU and the three free molex cables? I saw some split cable giving two additional SATA cables per molex.:

https://www.amazon.co.uk/Molex-Internal-Power-Splitter-Cable/dp/B0066DA9N8

 

How many drives can I put to one molex and how many drives in total for that PSU?

 

Thanks in advance.

 

[DieFalse]

Calculate at 20watts per drive and make sure the rail can handle it on the PSU.

[pwm]

The linked PSU has two 12V rails so if you want to use many drives, then you need to make sure the load is split over the two rails.

[Squid]

31 minutes ago, pwm said:

The linked PSU has two 12V rails so if you want to use many drives, then you need to make sure the load is split over the two rails.

The manual doesn't specify though what 12v1 and 12v2 handle though. 

 

Its pretty much a guarantee that any and all molex connectors / sata connectors are all going to be on the same rail.  The question becomes which rail the GPU and CPU is run from.

[pwm]

3 minutes ago, Squid said:

The manual doesn't specify though what 12v1 and 12v2 handle though. 

 

Its pretty much a guarantee that any and all molex connectors / sata connectors are all going to be on the same rail.  The question becomes which rail the GPU and CPU is run from.

They claim 24A and 21A for the two rails. But it's correct that they do not mention which of the two rails that is used for the different molex/sata cables - this makes it hard to know how to balance the load.

 

One note is that the ATX standard demanded multiple rails for larger supplies (to limit the maximum current and reduce the danger of fire), but lots of manufacturers decided to ignore this and internally designed a single rail anyway because that is cheaper. The only way to actually know is to look on the inside if there are multiple 12V sources or if all 12V comes from a single point.

[Squid]

Just now, pwm said:

But it's correct that they do not mention which of the two rails that is used for the different molex/sata cables - this makes it hard to know how to balance the load.

Old, old server I used to tap into the GPU feed (unused) for its 12v

[hawihoney]

Thanks for your answers. However I did not understand one single word 8-)

 

Just a guess? Five drives are on the SATA cable (~100W). The motherboard connector gives power to one single fan only (?W). Would four additional drives work with a molex cable (~80W)? Or eight additional drives with two molex cables (~160W). BTW, 20W sound alot for a modern drive (Toshiba 6TB X300, WD 6TB EZFR?).

 

These totals would stay way below the 500W of the PSU and are nearly the half of the 500W. Should I try - at least the four additional drives?

 

Thanks again.

 

 

Edited March 21, 2018 by hawihoney

[Squid]

19 minutes ago, hawihoney said:

WD 6TB EZFR?

Its all about spin up current.  This drive's rated spinup current is 1.79A which is 21.48 Watts.   Personally, I think it's pointless looking at wattage, because confusion results in the total wattage of a powersupply vs what the power supply can handle on any given rail, especially since the specs listed for any power supply are always in amps.

 

So, all else being equal and on a brand-new supply (as the capacitors age they cannot handle their max rated current anymore), your linked supply @ 21A can handle ballpark 10 drives on that rail.

[hawihoney]

Thank you very much. I think it's better to stay below 10. I try and start with 8. Good news.