Has anyone tried modifying a 110v atx PSU to 12v DC?

HappyPuppy · 11-07-2000, 11:50 AM

Hey guys, just wondering if anyone has looked into this. I mean, it has to be converted to dc power somewhere in the circuit. doesn't it?

Chris Snyder · 11-07-2000, 04:00 PM

It would probably be cheaper (time-wise) to just buy a DC-DC.

Catlas · 11-07-2000, 04:44 PM

This had bee discussed in previous posts...look thru the archives and maybe you'll find something. If I remember correctly it was determined that it would be an innefective solution.

Catlas

Dima · 11-08-2000, 01:19 AM

It can be done,but it would make the same noise like inverter,because of different grounds.I tried it,doesn't worth it.Save yourself a lot of problems and go to DC-DC, I recommend on Sproggy's one.

Aaron Cake · 11-08-2000, 10:11 AM

Quote:

Originally posted by Dima:
It can be done,but it would make the same noise like inverter,because of different grounds.I tried it,doesn't worth it.Save yourself a lot of problems and go to DC-DC, I recommend on Sproggy's one.

What do you mean it can be done? Doing so would require a complete redesign of the first stage of the supply (rectification, filtering, and the switching circuit). The only useable part of the circuit would be the final regulating stage. Even then I doubt that it would work. If it did, you would basically have a DC-DC converter (which is what a switching supply is anyway).

------------------
Aaron Cake
London, Ontario, Canada

Player: Cyrix 200, 32MB RAM, 10.2Gig Quantum HD, Onboard EtherNet/Sound/Video, Custom Lexan Case, Arise DC-DC, Win95 Kernal w/Custom Player
Car: '86 Mazda RX-7 w/Basic Performance Upgrades

HappyPuppy · 11-08-2000, 01:54 PM

I've checked out sproggy's MK2.5--it's a nice design, but it's power ratings don't come close to what i need. I'm setting up a PII 400, 256 MB RAM, NEC 4x4 CDROM Changer, Pioneer slot-load DVD, Zip Drive, 4 gig IDE, Voodoo 3 3000, SB Live Value, VHX TV/FM card, Diamond HomeFree wireless LAN, the DiscoLitez 32-light LPT circuit, and a serial port Rockwell GPS. I wish I could use that one, but I can't figure out how I'd meet my total power reqirements.

If I can't find plans for a high capacity one, I'm going to be forced to buy SunPower's 100 watt DC atx supply at $102 =(

BTW, I've scoured every reference to DC power supplies in this msg board--I found plenty of high-powered commercial PSUs, and a whole bunch of low power Maxim-based plans, but I never found any high powered kits.

Falcon62Travis · 11-09-2000, 12:07 AM

The one I bought at http://www.industrialpcs.com/p_suppl...7004_12_24.htm
is a 70 watt DC-DC psu for $60 and $4 shipping. It came about 4 days after I ordered it. The best part about this psu for your setup is it comes with two connector cables, one with connections for the motherboard HD, Floppy... The other one has just HD, Floppy connectors.
So it looks real easy to use more than one to get all the power you need.

Dima · 11-09-2000, 12:44 AM

Quote:

Originally posted by Aaron Cake:
What do you mean it can be done? Doing so would require a complete redesign of the first stage of the supply (rectification, filtering, and the switching circuit.

You don't need to redesine the circuit.What I did was making a 50hz sine wave generator (it's 220v here) producing 220v through transformer,and putting it to the input of AT PSU.This is very similar to inverter. There were a few problems:you have to use quite a big transformer because of large currents,and it makes some buzzing noise,probably because the generator didn't produce pure sine wave.
HappyPuppy:yes,it seems like you need a very powerful PSU.If you have some idea in electronics you can redesign the Sproggy's DC-DC to make it more powerful.The most current "hungry" voltages are 5v and 12v.If you know using Protel,you can add more 5v and 12v sections to the circuit.

Aaron Cake · 11-10-2000, 10:33 AM

Quote:

You don't need to redesine the circuit.What I did was making a 50hz sine wave generator (it's 220v here) producing 220v through transformer,and putting it to the input of AT PSU.This is very similar to inverter. There were a few problems:you have to use quite a big transformer because of large currents,and it makes some buzzing noise,probably because the generator didn't produce pure sine wave.

So all you did was build an inverter? This has exactly the same problem as running a commercial inverter. Namely, innefficiency and noise.

For all that trouble, a $79 DC-DC converter sounds better and better...

------------------
Aaron Cake
London, Ontario, Canada

Player: Cyrix 200, 32MB RAM, 10.2Gig Quantum HD, Onboard EtherNet/Sound/Video, Custom Lexan Case, Arise DC-DC, Win95 Kernal w/Custom Player
Car: '86 Mazda RX-7 w/Basic Performance Upgrades

HappyPuppy · 11-10-2000, 12:52 PM

Well, the Industrial PCs idea would be good for an at PSU, but the only two DC ATX PSUs they sell are for 24 and 48 volt systems, and I don't feel like trying to wire THAT up.

If some one could let me "examine" a copy of this Protel, I might try my hand at designing a real bad boy PSU, something that can really handle some major wattage. After all, who here JUST wants a MP3 Player?

xa0s · 11-10-2000, 07:29 PM

Why not just build a 3.3volt stepdown with a MAX788 and run it off of an AT DC/DC power supply or from the cars 12volt source? This way you can get the 3.3volt source for an atx board, and then just wire it into a standard ATX connector? Just a thought!

HappyPuppy · 11-10-2000, 08:01 PM

It sounds like a wonderful idea, but I have a couple of worries. My main concern is the whole "power good" circuit. What is it and does an ATX PC need it? I think its like -5v or something like that. So far, the cheapest price I have heard for a DC-DC ATX PSU is $102.

Aaron Cake · 11-11-2000, 10:42 AM

Power Good is 5V, activated about 100mS after the supply voltages stabilize. You can mimick the signal with a simple RC network.

------------------
Aaron Cake
London, Ontario, Canada

Player: Cyrix 200, 32MB RAM, 10.2Gig Quantum HD, Onboard EtherNet/Sound/Video, Custom Lexan Case, Arise DC-DC, Win95 Kernal w/Custom Player
Car: '86 Mazda RX-7 w/Basic Performance Upgrades

HappyPuppy · 11-11-2000, 12:27 PM

RC? As in Resistor Crossover maybe? I'm a pretty dedicated cheapskate, so if I can glean enough info to design a big PSU, I'll do it and post the design. So far, I'm thinking about modifying Sproggy PSU, daisy chaining the MAX ICs to gain more power handling (if that's possible). That would take care of the power issue, but as for the power good signal, i don't know

Rob Withey · 11-12-2000, 10:03 AM

RC as in Resistor-Capacitor I would guess. Use an inline resistor from the 5V line to charge a capacitor. The voltage on the capacitor rises more slowly than the voltage before the resistor. This still gives you a slowish edge - a schmitt trigger would sharpen this up if this still causes grief.

The delay can be altered by the values of R and C. Bigger R means smaller charge current and a longer delay. Bigger C means more charge needed to raise the voltage on the capacitor, and a longer delay.

Rob

Quote:

Originally posted by HappyPuppy:
RC? As in Resistor Crossover maybe? I'm a pretty dedicated cheapskate, so if I can glean enough info to design a big PSU, I'll do it and post the design. So far, I'm thinking about modifying Sproggy PSU, daisy chaining the MAX ICs to gain more power handling (if that's possible). That would take care of the power issue, but as for the power good signal, i don't know

------------------
-- <A HREF="http://www.nav.to/robwithey" TARGET=_blank>http://www.nav.to/robwithey
</A>