How to Boost 11.8V to 12V at 1A for Old HDD Using Commodore 64 Power Supply?

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#1 21659847 06 Oct 2011 09:47

Stephen Shaffer Stephen Shaffer

Anonymous
Post #1
21659847 06 Oct 2011 09:47

Hey guys! I have an old Commodore 64 power block, and I am trying to use it to power some old recycled hard drives. The power block has +5v, -5v, +12v and -12v, the problem however is the +12v is measured at 11.8v, and the hard drive tries to spin up but then stops. On my lab PSU, the same thing happens at 11.8, but then as soon as I turn it up to 12v, it runs!
I really want to use this Commodore 64 power block for retro looks, I am willing to strip the guts and build my own PSU, however if there is a simple way to step up the voltage (and still have the 1 Amp pf start up current necessary to run the hard drive) I would be interested to know how.
This is all for a POV HDD clock, attached is it working so far. The +12v source for the HDD had to come from my lab PSU in order to test the programming.
Thanks for any suggestions!

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#2 21659848 06 Oct 2011 10:32

Ralph Pruitt Ralph Pruitt

Anonymous

Post #2
21659848 06 Oct 2011 10:32

On your 12V Power supply(Commodore 64 power block), what are the driving specs(Current) of the power supply? Also what are driving specs(Current) for the Hard Disk? Are you trying to drive a load that the power supply just by the nature of the underlying design and parts will not be able to meet that load.....ie...Need more info to help.....
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#3 21659849 06 Oct 2011 10:55

Per Zackrisson Per Zackrisson

Anonymous

Post #3
21659849 06 Oct 2011 10:55

The problem is in your HD.
It should work on 11.8 Volts.
Or somewhere else, even a new ATX2.2 standard specify 12V -+5%. So it may not work even if you buy a new PSU.
So you can not rely on your HD!
I would not put any data worth saving on that HD.
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#4 21659850 06 Oct 2011 11:13

Stephen Shaffer Stephen Shaffer

Anonymous

Post #4
21659850 06 Oct 2011 11:13

I suppose you are right, I just watched it die at 12v. Perhaps there was a lack of current capabilities which caused it to burn out. The C64 block was rated at 1amp at 12v, the hard drive however had no amp ratings on it, which I found odd, as almost all my other ones laying around do, but I chose this one for size requirements on spindle height for the stepper motor within.
#5 21659851 06 Oct 2011 13:17

Ralph Pruitt Ralph Pruitt

Anonymous

Post #5
21659851 06 Oct 2011 13:17

Ouch......Good luck on the repair of the module.....
#6 21659852 06 Oct 2011 23:26

David Deleonardo David Deleonardo

Anonymous

Post #6
21659852 06 Oct 2011 23:26

Here is a simple way to raise the output by the small amount you are asking for: find where the supply is sampling the output voltage and change it! The simplest way would be to change the resistor divider ratio by soldering an additional resistor on top of the "bottom" resistor in the divider chain. (It is the one that is connected from ground and the feedback input.)

Good luck on your hack.
#7 21659853 21 Oct 2011 05:55

Siraj A Siraj A

Anonymous

Post #7
21659853 21 Oct 2011 05:55

Exactly it should work on 11.8 volts.
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#8 21659854 23 Oct 2011 04:39

Frank Bushnell Frank Bushnell

Anonymous

Post #8
21659854 23 Oct 2011 04:39

What died ... the PSU or the HD ?

(If not the HD, check its current draw on startup and running with a more powerful 12V supply.)

(If not the PSU, check its current capability and voltage drop with increasing load to determine its useful power rating.)
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Topic summary

A user attempts to power an old hard drive using a Commodore 64 power supply, which outputs +12V measured at 11.8V. The hard drive fails to spin up properly at 11.8V but works at a true 12V from a lab power supply. The Commodore 64 PSU is rated for 1A at 12V, but the hard drive's current requirements are unknown. Discussion highlights that many hard drives and even modern ATX power supplies tolerate ±5% voltage variation, so 11.8V should generally be sufficient. The hard drive may have failed due to insufficient current or other issues. A suggested solution to increase the PSU output voltage slightly is to modify the feedback resistor divider in the PSU by adding a resistor to raise the output voltage above 11.8V. Further advice includes verifying the current draw of the hard drive at startup and under load, and testing the PSU's current capability and voltage stability under load to ensure it meets the hard drive's requirements.
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How to Boost 11.8V to 12V at 1A for Old HDD Using Commodore 64 Power Supply?

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