Results 1 to 6 of 6

Thread: Power output of A500 Power Supply

  1. #1
    snoopy77's Avatar
    Join Date
    Jul 2013
    Country
    Australia
    Region:
    Melbourne
    Posts
    146
    Feedback
    3 (100%)

    Default Power output of A500 Power Supply

    Have read comments before that A500 power supplies are either 25 watts or 35 watts.

    I have a "heavy" A500 power supply from about 1990,

    On the back it doesn't state a power output but the input as shown in the photo is stated as "60W",

    So I'm curious, is the power output actually 35watts, 60 watts or 25 watts, what do you think?

    Click image for larger version. 

Name:	IMG_9282.JPG.jpg 
Views:	9 
Size:	189.3 KB 
ID:	142858


    btw the part number is stated as 312503-05 (a higher part number than the two variants on Ian Stedman's site)
    Last edited by snoopy77; 7th January 2019 at 08:55.
    Only Amiga Makes it Possible!

    A1200, Indivision MKIICR, Blizzard 1230 IV 32mb
    A500 rev 6a, ACA500+ 42/8mb, Indivision ECS, 512k ram exp, broken Roctec Roclite Ext FDD

  2. #2
    8 Bit Dreams DjCook's Avatar
    Join Date
    Apr 2016
    Country
    Germany
    Region:
    Bavaria
    Age
    40
    Posts
    1,248
    Feedback
    105 (100%)

    Default

    It's 60W cause 5v and 12v rails are counted together.
    Most important is 5v rail, yours is 4.3A, just recap it, do a voltage measure DIRECTLY at CPU on running system 4.8v is bad do adjustment, should be 4.95v ideally
    Last edited by DjCook; 7th January 2019 at 09:08.
    repairs of retro computers & hardware in Germany

  3. #3
    Amibayer! Bryce's Avatar
    Join Date
    Aug 2012
    Country
    Germany
    Region:
    Nordrhein Westfalen
    Posts
    2,170
    Feedback
    78 (100%)

    Default

    Quote Originally Posted by DjCook View Post
    It's 60W cause 5v and 12v rails are counted together.
    Most important is 5v rail, yours is 4.3A, just recap it, do a voltage measure DIRECTLY at CPU on running system 4.8v is bad do adjustment, should be 4.95v ideally
    Not quite...
    The 60W refers to how much power it pulls from the socket. To this you need to add all the losses (heat etc) inside the PSU. The actual output power can be easily measured with simple maths: P(power in watts) = I (Amps) x V (Voltage). So in your case:

    5V Rail: P = 4.3 x 5 = 21.5 Watts
    12V Rail: P = 1 x 12 = 12 Watts
    -12V Rail: P = 0.1 x 12 = 1.2 Watts
    Total: 34.7 Watts.

    This means that the PSU is dissapating 25.3 Watts of wasted energy as heat/noise/eddy currents etc and the efficiency of the PSU is a rather poor 57.8%
    However, it's probably not that bad as the 60W spec is a max requirement, not what it actually needs in reality.

    Bryce.
    Last edited by Bryce; 7th January 2019 at 09:54.

  4. #4
    snoopy77's Avatar
    Join Date
    Jul 2013
    Country
    Australia
    Region:
    Melbourne
    Posts
    146
    Feedback
    3 (100%)

    Default

    Thanks guys!
    Only Amiga Makes it Possible!

    A1200, Indivision MKIICR, Blizzard 1230 IV 32mb
    A500 rev 6a, ACA500+ 42/8mb, Indivision ECS, 512k ram exp, broken Roctec Roclite Ext FDD

  5. #5
    slaz's Avatar
    Join Date
    May 2010
    Country
    UK
    Region:
    London
    Age
    63
    Posts
    362
    Feedback
    30 (100%)

    Default

    ... and just a FYI - I understand some of the later ones are SMPSU design (switch-mode) - the light weight ones.

    These should be a good deal more efficient - i.e. the power input would be much closer to the power output. So a PSU rated at 35W output would have power input more like 40W. Less heat also - but possibly more failure-prone if they use cheapish components.
    Last edited by slaz; 9th January 2019 at 04:08.

  6. #6
    Amibayer! Bryce's Avatar
    Join Date
    Aug 2012
    Country
    Germany
    Region:
    Nordrhein Westfalen
    Posts
    2,170
    Feedback
    78 (100%)

    Default

    A well designed SMPSU can be more than 90% efficient, but I don't know if the Amiga ones were that good. They didn't use very cheap components and they are generally well designed and have enough room to keep cool, so they should be pretty reliable too.

    Bryce.

Similar Threads

  1. Replies: 8
    Last Post: 23rd March 2018, 11:07
  2. Replies: 0
    Last Post: 28th October 2016, 05:45
  3. Replies: 43
    Last Post: 11th April 2016, 10:50
  4. Wanted A500 power supply
    By ST-Freakz in forum Amiga
    Replies: 1
    Last Post: 2nd July 2015, 19:53
  5. Replies: 15
    Last Post: 2nd March 2010, 03:04

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •