Post by thread:[EE]: ATX power suply

Hello, I'm needing a 10V/24A power supply and noticed most modern ATX (PC computer) power supply have a 5V/25A and a 12V/10A outputs. It would be easy to change an ATX power supply for 10V output? What about using two suplies with it's 5V outputs in series? Thank you very much, Brusque ----------------------------------------------------------------- Edson Brusque C.I.Tronics Lighting Designers Ltda Research and Development Blumenau - SC - Brazil Say NO to HTML mail http://www.citronics.com.br ----------------------------------------------------------------- -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Edson Brusque (Listas) wrote: > I'm needing a 10V/24A power supply and noticed most modern ATX (PC > computer) power supply have a 5V/25A and a 12V/10A outputs. > It would be easy to change an ATX power supply for 10V > output? What about using two suplies with it's 5V outputs in series? AT power supply is cheaper, I think. You may rewind 5v coil with thinner wire and 12v with thicker. Then change 12v/10A diodes with 12v/25v. Then adjust 5v by some resistor to lower value (~4v). This drops 12v to 10v. For more accuracy you may switch regulator loop from 5v to 12v output. Mike. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

You shouldn't try to put them in series, at minimum they are grounded and you'd have to defeat at least one of the grounds to connect them. The supply typically only regulates one output (5v or 3.3v) and depends on the transformer windings to generate the other voltages relative to the 5v winding. To change the 12v to 10v, you'll likely need to rewind one of the transformers. Alternately, put some 24A diodes with specified votlage drops in the 12v line. They would need to drop 2v at 24A, or 50W or power and would thus need beefy heat sinks and a fan. But such a module could still be fairly small - possibly fitting inside the powersupply if needed, using the power supplies own fan. Don't try to parallel the diodes to reach the current. You can do it if you carefully match them and use balancing resisters, but it's always a messy fix for something that can be done easily and cheaply with proper diodes. -Adam Edson Brusque (Listas) wrote: {Quote hidden}>Hello, > > I'm needing a 10V/24A power supply and noticed most modern ATX (PC >computer) power supply have a 5V/25A and a 12V/10A outputs. > > It would be easy to change an ATX power supply for 10V output? What >about using two suplies with it's 5V outputs in series? > > Thank you very much, > > Brusque > >----------------------------------------------------------------- >Edson Brusque C.I.Tronics Lighting Designers Ltda >Research and Development Blumenau - SC - Brazil >Say NO to HTML mail http://www.citronics.com.br >----------------------------------------------------------------- > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

M. Adam Davis wrote: . . > Alternately, put some 24A diodes with specified > votlage drops in the 12v line. They would need > to drop 2v at 24A, or 50W or power and would > thus need beefy heat sinks and a fan. . . M. Adam Davis, no 2v dropped, since this is not bridge (or how is it called with 4 diodes in English). Only 2 diodes at the endings of winding, the middle of the winding is grounded. Moreover diodes should be low voltage Shottky, optimized for 25A. So would be dropped approx 0.5v, if I'm not mistaken. Mike. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

I'm not sure you understand (or I don't understand) If you leave the innards of the supply alone, and put two 1.0 volt drop diodes in the positive line (in series with the load) then the load would see a regulated 10V, since the diodes would drop two volts. If you put a bridge rectifier on the output of the DC supply, you'll still have two diodes in series with the supply (and thus the load would see 10v), but your circuit ground would be 1 volt above the power supply ground, and thus one volt above earth (since the power supply ground is earthed). However, the diodes I've seen have drops of 1.1v at that amperage. Schotky diodes would have a lower drop, but I doubt he'll get exactly 10v, more like 9.8 to 10.2 volts. Using two 1.05 drop diodes will get you 9.9 volts, which is just barely within 10% (pretty far from regulation, but perhaps usable for the project). Of course, you can simply mess with the voltage regulator in the supply (since only one voltage is actually regulated) and tune it down to 10v. -Adam Mike Singer wrote: {Quote hidden}>M. Adam Davis wrote: >. >. > > >>Alternately, put some 24A diodes with specified >>votlage drops in the 12v line. They would need >>to drop 2v at 24A, or 50W or power and would >>thus need beefy heat sinks and a fan. >> >> >. >. > M. Adam Davis, > > no 2v dropped, since this is not bridge (or how >is it called with 4 diodes in English). Only 2 diodes >at the endings of winding, the middle of the winding >is grounded. Moreover diodes should be low voltage >Shottky, optimized for 25A. So would be dropped >approx 0.5v, if I'm not mistaken. > > Mike. > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > Of course, you can simply mess with the voltage regulator in the > supply (since only one voltage is actually regulated) and tune it > down to 10v. Wouldn't that be the 5V supply since it has the highest load? - --Brendan -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 6.5.8 for non-commercial use <http://www.pgp.com> iQA/AwUBPUFyqAVk8xtQuK+BEQKxMQCfY+jEIQwxoJD9xnlpKDEwwyNW0T4AnROh LBfnzKyf05FD3AecjrToW7u0 =HLJz -----END PGP SIGNATURE----- -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

It may be that the 3.3v supply is the regulated one. Either way find out where the regulator is, and how it's controlled. It should be noted that switching regulators designs (and the coils/components) have the voltage and current designed in. Messing with the regulator and changing the voltage could have serious effects on the overall design (ie, lower current supply, more ripple, not as well regulated, etc). -Adam Brendan Moran wrote: {Quote hidden}>-----BEGIN PGP SIGNED MESSAGE----- >Hash: SHA1 > > > >>Of course, you can simply mess with the voltage regulator in the >>supply (since only one voltage is actually regulated) and tune it >>down to 10v. >> >> > >Wouldn't that be the 5V supply since it has the highest load? > >- --Brendan > >-----BEGIN PGP SIGNATURE----- >Version: PGPfreeware 6.5.8 for non-commercial use <http://www.pgp.com> > >iQA/AwUBPUFyqAVk8xtQuK+BEQKxMQCfY+jEIQwxoJD9xnlpKDEwwyNW0T4AnROh >LBfnzKyf05FD3AecjrToW7u0 >=HLJz >-----END PGP SIGNATURE----- > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

Yes, I didn't realize you proposed diodes for dropping 12v to 10v. I thought, that you just calculated increased power dissipation when replacing 10A to 25A diodes. I don't think using diodes for dropping voltage is a good idea, since anyway transformer should be disassembled and coils rewinded with thicker wire for 10v. Anyway the voltage regulator loop should be transfered from 5v to 10v, as 25A is too much to be regulated indirectly. Mike. M. Adam Davis wrote: {Quote hidden}> I'm not sure you understand (or I don't understand) > > If you leave the innards of the supply alone, and put two 1.0 > volt drop > diodes in the positive line (in series with the load) then the load > would see a regulated 10V, since the diodes would drop two volts. > > If you put a bridge rectifier on the output of the DC supply, you'll > still have two diodes in series with the supply (and thus the > load would > see 10v), but your circuit ground would be 1 volt above the > power supply > ground, and thus one volt above earth (since the power supply > ground is > earthed). > > However, the diodes I've seen have drops of 1.1v at that amperage. > Schotky diodes would have a lower drop, but I doubt he'll get exactly > 10v, more like 9.8 to 10.2 volts. Using two 1.05 drop diodes will get > you 9.9 volts, which is just barely within 10% (pretty far from > regulation, but perhaps usable for the project). > > Of course, you can simply mess with the voltage regulator in > the supply > (since only one voltage is actually regulated) and tune it > down to 10v. > > -Adam > > Mike Singer wrote: > > >M. Adam Davis wrote: > >. > >. > > > > > >>Alternately, put some 24A diodes with specified > >>votlage drops in the 12v line. They would need > >>to drop 2v at 24A, or 50W or power and would > >>thus need beefy heat sinks and a fan. > >> > >> > >. > >. > > M. Adam Davis, > > > > no 2v dropped, since this is not bridge (or how > >is it called with 4 diodes in English). Only 2 diodes > >at the endings of winding, the middle of the winding > >is grounded. Moreover diodes should be low voltage > >Shottky, optimized for 25A. So would be dropped > >approx 0.5v, if I'm not mistaken. > > > > Mike. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

I agree that the uneven load (little load on 5v, heavy load on 12v) would be bad, but I suspect that since most new motherboards use the 12v extensively (and sometimes more than the 5v) then it may not be a problem - obviously something that would need to be tested. Why would the coils need to be rewound with thicker wire? They are still seeing the same voltage and current (12v at 24A). The diode drop shouldn't affect them at all... -Adam Mike Singer wrote: {Quote hidden}> Yes, I didn't realize you proposed diodes for dropping >12v to 10v. I thought, that you just calculated increased >power dissipation when replacing 10A to 25A diodes. > I don't think using diodes for dropping voltage is a good >idea, since anyway transformer should be disassembled >and coils rewinded with thicker wire for 10v. > Anyway the voltage regulator loop should be transfered >from 5v to 10v, as 25A is too much to be regulated >indirectly. > > Mike. > >M. Adam Davis wrote: > > > >>I'm not sure you understand (or I don't understand) >> >>If you leave the innards of the supply alone, and put two 1.0 >>volt drop >>diodes in the positive line (in series with the load) then the load >>would see a regulated 10V, since the diodes would drop two volts. >> >>If you put a bridge rectifier on the output of the DC supply, you'll >>still have two diodes in series with the supply (and thus the >>load would >>see 10v), but your circuit ground would be 1 volt above the >>power supply >>ground, and thus one volt above earth (since the power supply >>ground is >>earthed). >> >>However, the diodes I've seen have drops of 1.1v at that amperage. >> Schotky diodes would have a lower drop, but I doubt he'll get exactly >>10v, more like 9.8 to 10.2 volts. Using two 1.05 drop diodes will get >>you 9.9 volts, which is just barely within 10% (pretty far from >>regulation, but perhaps usable for the project). >> >>Of course, you can simply mess with the voltage regulator in >>the supply >>(since only one voltage is actually regulated) and tune it >>down to 10v. >> >>-Adam >> >>Mike Singer wrote: >> >> >> >>>M. Adam Davis wrote: >>>. >>>. >>> >>> >>> >>> >>>>Alternately, put some 24A diodes with specified >>>>votlage drops in the 12v line. They would need >>>>to drop 2v at 24A, or 50W or power and would >>>>thus need beefy heat sinks and a fan. >>>> >>>> >>>> >>>> >>>. >>>. >>> M. Adam Davis, >>> >>> no 2v dropped, since this is not bridge (or how >>>is it called with 4 diodes in English). Only 2 diodes >>>at the endings of winding, the middle of the winding >>>is grounded. Moreover diodes should be low voltage >>>Shottky, optimized for 25A. So would be dropped >>>approx 0.5v, if I'm not mistaken. >>> >>> Mike. >>> >>> > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

M. Adam Davis wrote: > I agree that the uneven load (little load on 5v, heavy load on 12v) > would be bad, but I suspect that since most new motherboards > use the 12v > extensively (and sometimes more than the 5v) then it may not be a > problem - obviously something that would need to be tested. > > Why would the coils need to be rewound with thicker wire? They are > still seeing the same voltage and current (12v at 24A). The > diode drop > shouldn't affect them at all... PSU mentioned had 5V/25A and a 12V/10A outputs. If we want to double 12V-coil current, we are to double wire section (thicker wire). I do not see for what "new motherboards use the 12v extensively" - 3.3v for processor, chipset and AGP video. HDD is about 12V/0.5A. I can't predict what effect would be, when we place full load to 10v coil, trying to stabilize 5v. It is 5v coil, that is usually stabilized in AT PSU, if I'm not mistaken. So we should transfer stabilization to 12V coil. With old AT PSUs based on 494 chip it isn't a big problem. Mike. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Ah, I see. I didn't catch the initial supply specs. You are right that the windings (as well as other components) would have to be changed in order to yield more current from the 12v side. It may even be easier to mess with the 5v side and try to bring it up to 10v, but a rewind would probably be necessary for that as well. -Adam Mike Singer wrote: {Quote hidden}>M. Adam Davis wrote: > > >>I agree that the uneven load (little load on 5v, heavy load on 12v) >>would be bad, but I suspect that since most new motherboards >>use the 12v >>extensively (and sometimes more than the 5v) then it may not be a >>problem - obviously something that would need to be tested. >> >>Why would the coils need to be rewound with thicker wire? They are >>still seeing the same voltage and current (12v at 24A). The >>diode drop >>shouldn't affect them at all... >> >> > > PSU mentioned had 5V/25A and a 12V/10A outputs. >If we want to double 12V-coil current, we are to double >wire section (thicker wire). > I do not see for what "new motherboards use the 12v >extensively" - 3.3v for processor, chipset and AGP video. >HDD is about 12V/0.5A. > I can't predict what effect would be, when we place >full load to 10v coil, trying to stabilize 5v. It is 5v coil, that >is usually stabilized in AT PSU, if I'm not mistaken. > So we should transfer stabilization to 12V coil. With old >AT PSUs based on 494 chip it isn't a big problem. > > Mike. > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > > > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Although, at that point you're practically building the supply all over again. How about you ignore my advice I gave earlier and just put the outputs in series? You'll need to do the minimal work of seperating the output ground of the second supply from the input ground (and all other grounds), but it'll probably only be an hour project. Of course, there's never time to do it right - but there's always time to do it over. :-) -Adam Mike Singer wrote: {Quote hidden}>M. Adam Davis wrote: >. >. > > >>It may even be easier to mess with the 5v side >>and try to bring it up to 10v, but a rewind would >>probably be necessary for that as well. >> >> >. >. > Good idea, I think. >1.Throw avay all 12v output parts. >2.Rewind 5v coil with copper tape by twice turns. >3.Replace 5v output capacitors with those of higher voltages. >4.Diodes are already 25A. >5.Adjust regulating and overvoltage protection resistors. > > Mike. > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. > > > > > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.