Modifying an ATX power supply to output 25 on oen of the connector pins.

[Xandros]

So, to explain myself here, I want to take an ATX power supply and among some other modifications, mod it so that one of the pins on the 24 pin connector outputs +25v while on standby and powered up. Is this going to be an uphill struggle or would it be fairly straightforward?

The reason for me wanting to do this is because I have a PowerMac G4 (or to be more specific, a 2003 Mirror Drive Door) with an Cinema HD Display plugged into it's ADC port - these monitors don't have a separate PSU, they are instead powered through the ADC connector by the Mac. Thing is, these Macs are notorious for having PSU issues and failures and it seems mine has developed such an issue with its PSU. It does still work, but recently it just doesn't like driving the Apple Cinema HD Display I have plugged into it and won't turn on when it's plugged in. I have to fiddle around to get it to work with the monitor plugged in.

I figure if the PSU is on the way out it's only a matter of time before it dies completely anyway (it is afterall around 13 years old) so I'd like to replace the PSU. However replacement PSU's for these Macs are usually ridiculously expensive and it's cheaper by a long way to do an ATX conversion, and it's actually fairly straight forward to do an ATX conversion so it works in one of these Macs. The only problem with that is of course doing so means I'll lose the 25v power to the ADC connector rendering my monitor useless, hence my question here. It doesn't look like anyone else that's done an ATX conversion for their Mac has ventured down this avenue, or at least I can't find anything when Googling it.

I'm hopeful that isn't because it's not possible to do.

[Per Hansson]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

Use a DC>DC converter to go from 12v > 24v

[Xandros]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

That doesn't seem too complicated when you put that simply, but upon googling for potential parts I'm wondering if perhaps I'm a little out of my depth with that. Maybe I'd be better off for starters seeing if the old PSU has a bad cap or two and replacing them first (I did look, none appear to be bulged or leaking but I suppose that isn't concrete evidence they're OK).

[stj]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

how much current?

just go to DX or banggood and search "boost convertor"

[Xandros]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

I've got a feeling it's 4 amps. Those boost converters look more promising.

[stj]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

that will have to come from the 12v line.
and dont trust the sellers power ratings.
if you need 4A - buy one that claims 8A
you may get them cheaper on ebay btw.

[ozzy214]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

I got a couple old power supplies that run 24dc from printers. It has a barrel connector and you can find the suitable female for it to plug into. This way the monitor runs off that and the atx runs the puter. Then no need to modify a atx psu. I highly doubt 1 volt off will make a difference. And these have high amperage. Just cover postage 6.50 to throw it in a bubble mailer and its yours.

I dont want nothing other than that. Just pay it forward to the next man on the forum is all.

You want to go uber crazy I also just found a 40v dc power supply fir a old antenna rotator. The kind that rotates the good ole rabbit years on the pole. It boasts 80 watss of power and has screw terminals. I tried to power some hdtv leds last night and burn baby burnn.

So maybe that will help ya, let me know.

Just noticed you in england, the flat rate usps priority mailer is 16.00 i think overseas..not sure. I know its 6.50 in the states.

[stj]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

he would need 240v input

[TechGeek]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

yup, 240 to anything 120 would burn hotter than the sun...

[ozzy214]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

My bad, I keep forgetting we use 110v here and 220v there. Why is that anyway? I know they stop using dc, because voltage dropped over distance. But why the change with that?

[stj]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

higher voltage = lower current = thinner cables.
(but better insulation)

[joshnz]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

My bad, I keep forgetting we use 110v here and 220v there. Why is that anyway? I know they stop using dc, because voltage dropped over distance. But why the change with that?

it's cheaper to transport higher voltage / smaller cables less metal = less cost.

I always am wow when I watch a usa electrician say that they are changing there 100 amp panel (11.5KW) to a 200 amp panel(22KW).



Here 200 amps @ 230v is 46kw

most house services here are 60amp @ 230v so 13.8Kw

[TechGeek]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

Bridge 2 of the 12V lines together and put a 1V 4.7mfd capacitor in series with the 2 bridged 12V lines.

[stj]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

that's not likely to work, most psu's only have one 12v output internally.
(regardless of the rubbish printed on the label)

[jiroy]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

That's true . All the yellow wires (the 12v ) , are soldered together in one pack , and so is the red (the 5v +) ..

[budm]

Re: Modifying an ATX power supply to output 25 on oen of the connector pins.

Bridge 2 of the 12V lines together and put a 1V 4.7mfd capacitor in series with the 2 bridged 12V lines.

Even if it has actual two seperated 12V PS, What is the purpose of putting 4.7uF 1V in SERIES with the two 12VDC PS?