not quite audio but is used for audio purposes...

[Tasmaniak]

Right...my turn to ask for some help. lol
I mounted some terminals on the front of the PC a 12V a 5V.

I've fused the 12V side at 2A and the 5V side at 5A. This ok? Higher possible? or is it too much on the PSU? The specs on the side of the PSU state

+5v 22A
+12v 9A
-5v .5A
-12v .8A

I don't understand the negatives being a lower current handling then the positives. Should I be earthing it out to the chassis instead of the negatives in the loom?

If it's any help the PSU is running...

Prehistoric P3 500Mhz
15" monitor (obvious I know)
Serial port printer
Webcam
mouse and keyboard (obvious I know)
40X cd-rom, not burner (crappy I know)
Dual harddrives
3.5" Floppy (never used, I think I learnt about them in history class)
Sound card
D/U modem (no jokes please < note medieval smiley in use)
8mb sounds card


I'm not sure which of these items use what power source and how much current they draw. I'm not too keen on disconnecting them to find out. If someone is able to tell me how much current I can expect from the PC as a whole so I can determine what fuse ratings I should be using.

Thanks guys.

[Lano]

Ok, I *think* I grasped what you are doing, so I'll try and answer you.

Out of curiousity, what are the terminals on the front of your case for anyway?

Look here ( http://www.jscustompcs.com/power_sup....php?cmd=INTEL ) to see how much power your computer components will need. It will give you a rough idea. By the look of it you only have a 250 or 300 watt supply?

I'm pretty sure that the negative ratings on the P/S are for stuff like PCI cards, etc, and that the black cables that run to everything are just ground wires. The chassis and the wires are the a common ground, so it doesn't matter which one you ground it out to.
So unless you're hacking together a circuit board to go into a PCI slot, I wouldn't worry about the -ve voltages.

Personally I'd be putting in a higher wattage P/S.

Hope this helps

[Phreddy]

In fact, the negative supplies are used for nothing but communication ports. (RS232, Parallel, and so on) Lano, yes the black wires are all commoned to ground. The negative supplies are fed to the PCI slots, but only so that add-on cards with those comms type interfaces will work. Video card, sound card, and pretty much everything else only depend on +5 and +12, with a little +3.3V there as well.

Trunk, if you're only planning on pulling that much current you'll be fine. I couldn't tell you exactly how much current your PC components will pull (only 'coz I couldn't be bothered finding out), but as long as your power supply is 200-250W or better it'll have HEAPS of grunt left.

Cheerz!

[Tasmaniak]

Thanks guys. I basically need the power outputs on the front for a quick and easily accessible power supply. The power supply is only 250W but it seems to be coping just fine.

As a side note, I was told by a IT Tech friend in Melbourne when I asked him a little earlier in the night, NOT to use the chassis for an earth as it isn't quite the same earth...what ever the hell that means. Phreddy?

[dephilile]

I think they are not quite the same earth because it has to do with having negative outputs on your power supply. The negative 12 volts would actually be the same potential as your case. I’m not sure but.

[michaelw]

Don't use the PC case for 0V for the following reasons.

1)You could cause earth loops (hums and the like)
2)The 0V (what I will call the ground on the DC side) has nothing to do with the safety earth on the case, it may be connected by some weird filter cap thing or most likely through the metal on the shield grounds of the printer port et al.

As for the -ve supplies, about a million years ago PCs would use the negaive supply to power the serial ports and the harddrives. These days those things are looked after by dc-dc converters on the board. the negaive supplies are mostly kept there as a legacy thing. As a side note you could probaly do without them all together, as in the case of people potting a PC in their car.

[dephilile]

you could always try and find an old power supply and just sit it on your bench and use it for powering what ever you want. people are always throwing away old computers. a power supply from one of them would b fine.

[VS Omega]

dephilile is on to something, it's dead easy (on the 20 pin connector, just make a switch from the green cable and the black cable.. this will turn the PSU on), could make a nice case for it and rice it up lol

[Phreddy]

Some good comments there.

I think you could pick up earth from the case, but only if the motherboard is securely screwed to the chassis on a metal standoff. (good point you make Michael, but if the motherboard IS indeed screwed down firmly, then power supply ground IS at the same potential as chassis ground) An earth loop wouldn't be created if you just pick up ground for your external outputs from the chassis and don't connect it to the black wires out of the supply.

(if you use a meter and measure it, the pins on the motherboard which are connected to the black wires are also connected to the pads around the mounting holes. When I'm building a machine I make certain that the motherboard screws down firmly against the chassis, which then forces the connection between power supply ground and frame ground. Helps prevent some of the EMR too)

HOWEVER....

To make it all a bit easier Trunk, just pick it all up from a spare disk drive power plug - you have it all there. 5V on the red wire, 12V on the yellow one, and use either of the blacks for ground.

Cheerz!

[Tasmaniak]

Thanks for all the help and replies guys...

To make it all a bit easier Trunk, just pick it all up from a spare disk drive power plug - you have it all there. 5V on the red wire, 12V on the yellow one, and use either of the blacks for ground.

Cheerz!

Thats exactly what I've done, just added some fuses inline with it all....I can handle a short here and there but not one that could easily destroy my dodgy old PC, it tries hard to do that itself as it is!

Thanks again. Ray

[Tasmaniak]

Well, after all the effort I went too of getting it all in. (read as 5 minutes) I was poking around in there trying to create some room for a bigger hard drive when a shower of sparks came out of MY wiring. Killed the PSU completly....(turns out there was the tiniest, minutest smallest piddliest little bit of solder that had peirced through the heat shrink and shorted out against the chassis, turns out it was enough to do damage before the 5Amp fuse kicked in.

So, a fit of rage ensued and I knocked a box of wiring off the top the PC. I quickly replaced the PSU and to my surprise, everything worked fine! Phew!

I bent down to pick some of the wiring that fell. As I was shoving it all into the box I found a small desklight that had a 55W 12V downlight in it as a globe (one of those ones that mounts the light on two telescopic masts.) I plugged it in and nada, so I grabbed the meter and checked it and there was definetly 12Volts at the light socket. Good enough for me! So I ripped out the telescopic masts and quickly soldered a couple of fly leads in place. hooked up a 12V load....NADA...WTF?!

Pulled the case of the transformer apart and found that there was no regulator in there. I'd smashed the one out of the globe housing because I didn't know it was in there. I quickly grabbed four diodes made up a regulator and hey presto! A !_CHEAP_! 12V power supply!!

AND THEN

To top it all off, I figured if it had a 55W globe in there then sucker would be good 4-5amps. More then the PSU without the headaches! So I loaded it up up to 3 (fine) then 4 (fine) then 5(fine) then I put a 6amp load on there (fine) I thought well these lamps are like $20 so if I do happen to kill it, no probs at least I know what it's capable of. So I took it up 10 Amps!!!! No heating at all!!!!!!!!!!!!!! I then cranked it up higher (purely out of amusement now, you know how it happens) at 12 amps it stopped. I don't mean stopped working, I mean it has a current limiting circuit that wasn't going to allow me to draw anymore then 12amps out of it. Now, I don't know about you, but I can do a shitload more with 12amps then I ever could with 2amps.

So, hows that? a 13.2V power supply @ 12Amps for around 20 Bucks.....I think I might invest in a couple more of these...If I could find something with the same current handling but with about 15-16 Volts, it would be a CHEAP car charger eh?

[michaelw]

Voltage regulation would be shithouse and the ripple you look like a rollercoaster. But if it works for what you need then why spend up?

Mike

[Tasmaniak]

If the regulation and ripple gets too much then I will drop a capacitor inline with it.

[Tasmaniak]

still a damn sight better then forking out a couple of hundred for something along those lines.

[Phreddy]

Hey Trunk.

Throw a 1000-2200uF cap across it (electro, 25 Volt or so). You might find the voltage climbs a bit though, as the cap will charge to the peak.

Cheerz!