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Another computer fan question

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grrr_arrghh

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Hi again.

I am going to add some various fans to my computer (you may have seen my post about my unexpectedly powerful case fan...), but I'm not sure about the power that I can get from the +12v leads.

My power supply is a 400W switchmode ATX PSU. It has the usuall connections. However, I have 2 CD drives and 2 hard disks, so all four of the large drive connectors are used, and one of the small ones (for my floppy drive). Connectors in themselves aren't an issue, I can make adapters, however, the power I can get over one lead is an issue. I have posted the table that is on the side of my PSU. My PSU has five sets of leads coming out of it - standard ATX, auxilarly ATX, 2 HD/floppy (remembering that each HD/Floppy thing has two large and one small drive connector on) and one extra connector (with some orange leads and things...)

in total, therefore, there is 5 yellow (+12v) leads coming out of the PSU. Would these all be connected together inside the PSU? If so, can I load them up until I reach the max current for the 12v supply? Or can each lead take only their 'share' of the total (i.e. total current on 12v divided by 5)?

On one of the HD/Floppy sets of leads, I have 2 cd drives and one floppy drive. If I also connected a couple of fans to this set of leads, so you think this would cause any problems to the drives? (as long as I was not going above the max current). Which brings me onto my next question. How do I know how much current my various drives draw?

Thanks, all info and suggestions appreciated

Tim

P.S. If this doesn't make much sense, please tell me, and i will re-write it!! (its getting late...)
 

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The +12v @ 12a can come from just one or a combination of all of the available yellow connections as long as you don't exceed a total of 12a from all +12v loads combined. I have yet to see a computer supply (all of which have been switchers since IBMs original PC) that does not have all the +12v yellow wires soldered to the same foil on the supply board. Same goes for the other supply voltages and their respective color wires. All those yellow wires are taken back to that same point rather than "daisy chaining" through the connectors to reduce problems cause by current surges that could affect the voltage drop on a single wire and the subsequent effect on any loads connected to that same line.

Dean
 
oh, ok. Some of the leads are daisy chained, but not all.

And i suppose it would take a lot of HDs/CD drives to reach 12A!?!

Just out of interest...
If I did exceed 12A, what damage do you think this would do? (which components would it damage?)

Thanks a lot

Tim
 
On a vaguely related subject, does the speed of a fan depend on the voltage going to it, or the current?

also, one of my fans has a small thermistor, which presumably senses the temperature and controls the speed of the fan based on that. If I wanted to control the speed of the fan, so that the speed was a fraction of what it should be, I could use a current limiter/voltage divider (depending on the answer to the first question), but if I wanted to control the speed independent of the thermistor, I would have take out the onboard speed controlling circuit. Correct?

Thanks

Tim
 
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