Making Symmetric Power Supply from Single with 4x ATX power Supply?

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Hi i have 4 ATX power supplies that i connected in series and effectively got 48v DC. Removed ground connection from them and it is working. on first 0 is negative and +12 is connected to another and so on, last +12 is positive.

Question is can i use connection between second and third supply to get virtual ground for supplying AMP that needs +-25V. Voltages are good and it seams like +-24 V, but not sure if that can cause problems. All Supply's are rated to give 20A per 12v lin.
 
That is not safe. The metal chassis of the power supply must remain earthed for safety and for certain power line noise filtering ("Y" capacitors) to work correctly.

Inside your power supply there is a pair (or two) of "Y" line filtering capacitors, one from line to ground, and one from neutral to ground, intended to shunt noise from line/neutral into ground. By disabling the earth connection, you may have created a capacitive voltage divider between line and neutral with the power supply case in the middle. In other words, you power supply's metal case may be "live" with 1/2 of your mains voltage (240/2 = 120 VAC!).

To enable the low voltage output to float, you need to isolate the output ground (black wires) from the power supply's chassis, which must remain earthed. Most often, this connection is done on one or two of the mounting screws of the PCB. You will need to figure out how to isolate the power supply case from the output ground, while also ensuring that the PCB remains securely fastened. Be aware that there is a limitation of how far the output can float above or below earth without potentially exceeding the isolation capability of the power supply's transformer, which would result in risk of electrocution.
 
By disabling the earth connection, you may have created a capacitive voltage divider between line and neutral with the power supply case in the middle. In other words, you power supply's metal case may be "live" with 1/2 of your mains voltage (240/2 = 120 VAC!).
Thanks for quick reply, i am amazed how people want to help and share their experience and knowlenge. +1 to you.
I found out that chases are indeed hot, but not with half mains, but 12v. case is same as +12 on one power supply. There is a 12v difference between neibourgh modules and 48 between first and last. Also i have noticed that when switch off one of them voltage just drop by 12v... One strange thing, when conecting +5v in series i get exactly same thing but with 4x 5v, and 4x 3.3v when connect +3.3 in series.
 
Thanks guys, i will make some kind of isolation between cases and outside world... Right now it is not possible to buy toroidal transformer with such power (and would need aditional circuitry) so i guess i will be testing this on old LM3886 and will report back....
 
I'm not certain you have understood what we say. Cases must be grounded, not isolated. You don't seem to have grasped the difference between the various grounds in a circuit. To be blunt, if you knew enough to do all this safely you probably would not need to ask us.
Well i can isolate case from board and ground it. Question is would this work as symmetric power source for amp? I don't have higher understanding in this matter but only some basics, that is why i asked here. I do have voltages needed (-+24v) but i am concerned about impact on the amp and sound quality...
 
Sound quality is the least of your worries.

Please use the word (protective) earth instead of ground in this case to point out that the potential of the case IS connected to the mains earth in the wall outlet for SAFETY reasons.

It is not sufficient to break earth connection and put the supplies in a isolated outer casing. Actually it is illegal to remove the earth connection in most countries.

You would need to have an earth connection to the case, because if somethings goes wrong the casing can come live at high voltage potential , and perhaps also the low voltage output of 12V for many reasons which there is not sufficient space here to explain (creepage, clearance, arcing, loose wires etc )

At best you will then smoke all supplies + any attached amplifier.

At worst you or someone else or more will die either due to electrocution or in the ensuing fire.

So please read through macboy and the other posts
again, think it over and be sure you understand the differences of ground, earth and why the later is there before further experiments.
 
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