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Adding a second power supply RRS feed

  • Question

  • I have added a second power supply to my home-built WHS and it appears not to be powering on, since the fan is not on.  I am wondering if the reason is because I have only connected the SATA hard drive power leads and not connected any of the mainboard leads.  They of course are not needed, since the other power supply is powering the mainboard.

    It is a Silverstone TJ07 tower case.  It has 13 drive bays and room for two power supplies.  Originally I had a single power supply powering the mainboard and six SATA drives.

    I have since added two 4-port SATA controller cards (total of 8 more SATA ports).  I didn't really know whether my existing power supply could handle much more drives, but I figured 8 more would be too many, so I decided to add the second power supply.  For now I only have four additional drives I need to power.

    Both power supplies are Silverstone ST75F. 
    http://www.silverstonetek.com/products/p_contents.php?pno=st75f

    It's modular and 750 watts.  With the second power supply I only connected the power lead for the SATA drivess.  Every other lead is disconnected.  And the power supply appears not to power up.  The fan does not come on.

    So are power supplies meant to be used in this way, i.e. do I need to connect the mainboard in order for the power supply to function?  If not, then it looks like maybe it is defective.  Thoughts?
    Thursday, March 18, 2010 12:14 AM

Answers

  • If you really want to use both supplies then I would recommend contacting Silverstone. They made the case to accept two supplies and they made both supplies, so ask them if they sell a jumper or interconnecting cable assembly that was designed specifically for this use.

    However, I agree with Al's advice about one power supply closer to full-load being more efficient that two power supplies operating well below full-load, so if it were me I'd use only one supply.
    • Marked as answer by fje000 Thursday, March 18, 2010 3:28 PM
    Thursday, March 18, 2010 12:09 PM
  • Cases that support more than one PSU are usually to support motherboards that can have more than one power supply attached at a time.  If that is the case then your motherboard will have 2 off 20/24 Pin ATX Power Supply Connectors.

    However, if you still feel the need for two PSUs I came across this cable that would do the job for you:
    http://www.frozencpu.com/products/5637/cpa-167/Lian_Li_Dual_Power_Supply_Adapter_Cable.html

    PSUes typically get more efficient the higher utilisation they have towards full load - though you have to be careful that the load is distributed correctly across all voltage rails and in rush current (typically when switching on motors - i.e. fans and HDDs doesn't exceed the peak levels).

    Also using Molex to SATA convertors may not work as the newer ATX specs detail 3.3v and molex only provides 12/5v rails.

    Also my estimate of HDD power requirements on the 12v rail was 1.0A which is incorrect for a 3.5 Drive (I was thinking 2.5") it's close to 2.0A - I would guess your PSU can support above 20 drives without a struggle, though an email to SilverTone might be in order to check.

    Good luck,
    Al


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    • Marked as answer by fje000 Thursday, March 18, 2010 3:28 PM
    Thursday, March 18, 2010 1:23 PM

All replies

  • There are a pair of pins on the large connector that normally connects to the motherboard that need to be shorted together in order to turn the power supply on. You can get details from the link you posted. Click on "Downloads" and download the detailed specification sheet for the power supply. In your case pin 16 needs to be connected to pin 17. See specification 2.6 and Table 9.3.
    Thursday, March 18, 2010 12:44 AM
  • Is there a proper way to connect the two pins?  Something like a jumper maybe?  Does the connection conduct much current?
    Thursday, March 18, 2010 3:51 AM
  • Hi,

    Power supplies are not meant to be used like this.  I would not advise hacking together power supplies - you should upgrade you main power supply to one that can handle the extra drives. 

    However you only need another 12A on the 12V rail or so than normal to support 13 drives - the ST75F supports 60A over four rails so you have more than plenty of power in one power supply for your needs.

    I would advise you buy some SATA power splitters - didn't you post that you were using these:
    UK:
    http://www.google.co.uk/products?hl=en&q=SATA+Power+splitters&rlz=1I7GGLD_en&um=1&ie=UTF-8&ei=v_2hS9XzEJa8jAfkuoyHCg&sa=X&oi=product_result_group&ct=title&resnum=3&ved=0CCEQrQQwAg

    USA:
    http://www.google.com/products?hl=en&q=SATA+Power+splitters&rlz=1I7GGLD_en&um=1&ie=UTF-8&ei=v_2hS9XzEJa8jAfkuoyHCg&sa=X&oi=product_result_group&ct=title&resnum=3&ved=0CCEQrQQwAg

    By the way even if you did connect the two power supplies you would be powering two units with less efficency the using one power supply - so using the splitters will save you a bit of money over time (plus it will be a little quieter).

    Good luck,
    Al
    --
    Thursday, March 18, 2010 10:19 AM
  • If you really want to use both supplies then I would recommend contacting Silverstone. They made the case to accept two supplies and they made both supplies, so ask them if they sell a jumper or interconnecting cable assembly that was designed specifically for this use.

    However, I agree with Al's advice about one power supply closer to full-load being more efficient that two power supplies operating well below full-load, so if it were me I'd use only one supply.
    • Marked as answer by fje000 Thursday, March 18, 2010 3:28 PM
    Thursday, March 18, 2010 12:09 PM
  • Cases that support more than one PSU are usually to support motherboards that can have more than one power supply attached at a time.  If that is the case then your motherboard will have 2 off 20/24 Pin ATX Power Supply Connectors.

    However, if you still feel the need for two PSUs I came across this cable that would do the job for you:
    http://www.frozencpu.com/products/5637/cpa-167/Lian_Li_Dual_Power_Supply_Adapter_Cable.html

    PSUes typically get more efficient the higher utilisation they have towards full load - though you have to be careful that the load is distributed correctly across all voltage rails and in rush current (typically when switching on motors - i.e. fans and HDDs doesn't exceed the peak levels).

    Also using Molex to SATA convertors may not work as the newer ATX specs detail 3.3v and molex only provides 12/5v rails.

    Also my estimate of HDD power requirements on the 12v rail was 1.0A which is incorrect for a 3.5 Drive (I was thinking 2.5") it's close to 2.0A - I would guess your PSU can support above 20 drives without a struggle, though an email to SilverTone might be in order to check.

    Good luck,
    Al


    --
    • Marked as answer by fje000 Thursday, March 18, 2010 3:28 PM
    Thursday, March 18, 2010 1:23 PM
  • Mark and Al, great answers.  Thanks.

    I didn't really know what the single PSU would support, so rather than research it I just took the plunge and bought another.  With the money that I have been spending on this project, what was another 150 bucks!  I didn't really care that it was probably way over kill.

    I guess I'll give Silverstone a shot and see what they have to say.  In the mean time I don't have to have the extra drives mounted just yet.  Still have plenty of storage space without them for now.

    With the following

    >>Also using Molex to SATA convertors may not work as the newer ATX specs detail 3.3v
    >>and molex only provides 12/5v rails.

    it sounds like you are saying they would getting the wrong voltage on the SATA drives connected through Molex power lead with adapter.
    Thursday, March 18, 2010 3:53 PM
  • >>Also using Molex to SATA convertors may not work as the newer ATX specs detail 3.3v
    >>and molex only provides 12/5v rails.

    it sounds like you are saying they would getting the wrong voltage on the SATA drives connected through Molex power lead with adapter.

    I hope not - there just wouldn't be any 3.3v which perhaps a newer drive might need and perhaps why it won't spin up - I've not confirmed this myself just what I've read before.
    --
    Thursday, March 18, 2010 5:27 PM
  • However, if you still feel the need for two PSUs I came across this cable that would do the job for you:
    http://www.frozencpu.com/products/5637/cpa-167/Lian_Li_Dual_Power_Supply_Adapter_Cable.html


    --
    Apparently the TJ07 tower case came with such a cable.  It's been a while, so I had to dig through the pile of stuff collecting dust, but sure enough I found it.  Got everything hooked up and it is working fine.
    Thursday, March 18, 2010 8:43 PM