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12.6V from ATX instead of 12V?  Any ideas?
12.6V from ATX instead of 12V?  Any ideas?
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Old 29th October 2017, 04:18 AM   #1
kodabmx is offline kodabmx  Canada
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Default 12.6V from ATX instead of 12V? Any ideas?

I am using an ATX supply to power tube heaters and a couple of boost converters for B+. On LED supplies theres a voltage adjust trimmer. Does anyone know how to mod an ATX supply to give 12.6V? It's a Deepcool DA700.

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Old 29th October 2017, 04:22 AM   #2
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
why even bother? 12 volts is just fine.....
if you will take note, just loading the 5 volt rail increases the 12 volt rail up some....
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Old 29th October 2017, 10:36 AM   #3
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by kodabmx View Post
I am using an ATX supply to power tube heaters and a couple of boost converters for B+. On LED supplies theres a voltage adjust trimmer. Does anyone know how to mod an ATX supply to give 12.6V?
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Originally Posted by TonyTecson View Post
........
if you will take note, just loading the 5 volt rail increases the 12 volt rail up some....
I think that some/many ATX supplies use feedback from the +5Vdc line to determine the regulation of the whole SMPS.

If you were to move the NFB tapping to the +12Vdc line and adjust the feedback ratio, you should be able to safely change the output regulation this small amount.
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Old 29th October 2017, 10:58 AM   #4
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
they do, most of the atx psu i tested, the 12 volt rails are at 11.xx volts when tested shorting pin 14 to any ground pin ground, but use that psu on a pc and the rails actually go above 12 volts...

thus my recommendation to load the 5 volt rail, some atx even have a load built inside the psu a small load resistor, but to load the 5 volt rail with 1 ampere requires a 4.7 ohm 10 watt resistor..

no need to tamper with the innards of the ATX psu, it works off the line without isolation, very dangerous, so i will not recommend that you do it...
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Old 29th October 2017, 11:14 AM   #5
infinia is offline infinia  United States
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Quote:
Originally Posted by AndrewT View Post
I think that some/many ATX supplies use feedback from the +5Vdc line to determine the regulation of the whole SMPS.

If you were to move the NFB tapping to the +12Vdc line and adjust the feedback ratio, you should be able to safely change the output regulation this small amount.
ATX supplies don't work like that anymore. Ever since the all PC mainboards changed to use +12V to power the uProccesor. oh IDK 15 years ago? The newer PC supplies the 12V rail is the main feedback and they don't need pre-loading due to Intel sleep mode and other Green initiatives. Infact the newest ones have 5V and 3.3 DC/DC converters running off of the 12V rail.
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Last edited by infinia; 29th October 2017 at 11:19 AM.
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Old 29th October 2017, 11:20 AM   #6
AndrewT is offline AndrewT  Scotland
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Originally Posted by TonyTecson View Post
..............the innards of the ATX psu, it works off the line without isolation, very dangerous, so i will not recommend that you do it...
The ATX uses a transformer to ISOLATE the output from the mains.
The metal enclosure around an ATX SMPS is directly connected to the Protective Earth.

There is nothing dangerous about that !
Isolated and an effective Safety Earth for the exposed metal parts.
It complies with ClassI, so we bolt them into our desktop computers and don't have to worry about electric shock.
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Last edited by AndrewT; 29th October 2017 at 11:22 AM.
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Old 29th October 2017, 11:24 AM   #7
infinia is offline infinia  United States
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Quote:
Originally Posted by AndrewT View Post
The ATX uses a transformer to ISOLATE the output from the mains.
The metal enclosure around an ATX SMPS is directly connected to the Protective Earth.

There is nothing dangerous about that !
Isolated and an effective Safety Earth for the exposed metal parts.
Anyone who is familiar with offline switching supplies knows that half the board is fully charged at ~400Vdc and has no isolation. so yeah danger abounds.
As usual your words are sort of correct, but all wrong on any other practical level. The whole ball game changes when the OP talks about opening said "metal parts".
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Last edited by infinia; 29th October 2017 at 11:30 AM.
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Old 29th October 2017, 11:32 AM   #8
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
Infinia is right, obviously Andrew have not seen the innards of a psu to know that it works off the line without isolation, you can get zapped with the raw B+ of 300 volts dc and there in nothing between you and the main power lines...the thought scares me even though i have worked on a lot of those.....

Infinia, thanks for pointing out the 12 volt initiative by Intel, i almost forgot....
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Old 29th October 2017, 11:37 AM   #9
TonyTecson is offline TonyTecson  Philippines
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12.6V from ATX instead of 12V?  Any ideas?
Quote:
Originally Posted by AndrewT View Post
The ATX uses a transformer to ISOLATE the output from the mains.
The metal enclosure around an ATX SMPS is directly connected to the Protective Earth.

There is nothing dangerous about that !
Isolated and an effective Safety Earth for the exposed metal parts.
It complies with ClassI, so we bolt them into our desktop computers and don't have to worry about electric shock.
this assume that you are merely using the psu on a pc, not opening it and tinkering with the innards...

and i remember how you reported posts dealing with mains without isolation, changed you mind now?

the topic is still taboo here...
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Old 29th October 2017, 03:45 PM   #10
kodabmx is offline kodabmx  Canada
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Quote:
Originally Posted by infinia View Post
Anyone who is familiar with offline switching supplies knows that half the board is fully charged at ~400Vdc and has no isolation. so yeah danger abounds.
As usual your words are sort of correct, but all wrong on any other practical level. The whole ball game changes when the OP talks about opening said "metal parts".
It's powering a TUBE AMP! The B+ is 380V. Not worried about it at all.
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