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22nd Oct 2005, 3:17 pm | #1 |
Retired Dormant Member
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Ready made power supply unit
Having come into possession of an AT power unit from a scrap
computer, it occurred to me that it would form the basis of a low-voltage power unit for the bench. Outputs of +12 volt at 8 amp, +5 volt at 20 amp and –5 volt at 0.5 amp are available. These voltages are regulated and the unit has a built-in cooling fan. It must be an AT power unit and not an ATX unit as the latter do not have an on/off mains switch, being started by a circuit through the mother board. Has anyone ever tried this? As a test I connected a 12 volt 21w auto bulb across the 12 volt supply and it lit up with full brilliance with no sign of distress from the power unit. Royboy |
22nd Oct 2005, 4:03 pm | #2 |
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Re: Ready made power supply unit
Hi Roy. What you suggest is perfectly feasible. A while ago I sent an old AT PSU to a forum member who wanted to use it to power an LCD monitor (can't remember who it was now). The only thing to be cautious about is the current ratings, which often aren't for continuous operation, but if you derate by 50% everything should be OK.
You can also use them to power old car stereos to build a compact workshop or kitchen stereo. You can actually use ATX supplies too, but it's less straightforward. Best regards, Paul Last edited by paulsherwin; 22nd Oct 2005 at 4:13 pm. |
22nd Oct 2005, 7:05 pm | #3 |
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Re: Ready made power supply unit
It is important to have a load across at least one output at all times, otherwise the regulator circuits are a bit touchy....
Cheers Sean
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22nd Oct 2005, 10:55 pm | #4 | |
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Re: Ready made power supply unit
Quote:
The pinouts are on this page of the useful Hardware Book website. |
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23rd Oct 2005, 12:30 am | #5 | |
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Re: Ready made power supply unit
Quote:
Putting a few K across each output won't do any harm though Best regards, Paul |
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23rd Oct 2005, 10:00 am | #6 | |
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Re: Ready made power supply unit
Quote:
I used an AT power supply to power my ADSL router for a few months when the internal supply died. It needed something like 5V@2A, 12V@1A and -12V@0.5A which is a light load for a 300W supply, but it worked fine. The PSU was bigger than the router! I have now obtained a PSU that would fit inside during a clear-out at my old job. The only point I would make using a PC supply as a bench supply is that being switch-mode and cheaply made you'll probably find it's fairly noisy. So it may not be a good choice for analalogue electronics. Also they often don't have much/any short circuit or over-current protection (due to being made down to a price again), so if you short the 3.3V, 5V or 12V rails it may blow its internal fuse or fail more dramatically. |
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23rd Oct 2005, 12:17 pm | #7 | |
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Re: Ready made power supply unit
Quote:
Paul |
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23rd Oct 2005, 1:40 pm | #8 | |
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Re: Ready made power supply unit
Quote:
brunel Last edited by Paul Stenning; 23rd Oct 2005 at 9:01 pm. Reason: fixed quote |
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24th Oct 2005, 11:09 am | #9 |
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Re: Ready made power supply unit
Oops. I seemed to have started something. Many thanks to all who replied and gave valuable advice. I'm glad my idea has at least some merit.
I intended using the power supply to test car radios so I will give it a whirl as they say. Once again, many thanks to you all. Roy |
24th Oct 2005, 12:24 pm | #10 |
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Re: Ready made power supply unit
Always check the voltages with your expected loading as the 12V supplies are not always stabilised and can vary widely. Also note that with light load or a load balance that it doesn't like it can shut down - basically because of over-voltage protection which crow-bars the supply. Some supplies must then be left several minutes before recovering.
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24th Oct 2005, 1:00 pm | #11 | |
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Re: Ready made power supply unit
Quote:
I'm pretty sure the 12V supply is always stabilised, since the load presented by the disk drive motors will vary greatly during normal operation. Best regards, Paul |
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24th Oct 2005, 2:31 pm | #12 | |
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Re: Ready made power supply unit
Quote:
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24th Oct 2005, 3:31 pm | #13 |
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Re: Ready made power supply unit
If you take the cover off, no doubt you will see some very hefty stabiliser
I.C.'s. They look like large power transistors, all usually bolted to same heat sink. |