2 pc ps outputs in series?

I'm guessing that you're doing the "fan speed hack" to run the case fans more quietly at 7 V (12 -> 5) vice full speed (12 -> GND). If this is so then you're probably okay, with the caveat that you'll be introducing switching noise from the fan motor onto the 5V rail and additional filtering may be required/desired.

However, given the multitude of different power supply layouts and mainboard layouts, it's also possible that doing this will let the magic smoke out of something. There are too many variables to say for sure that doing this in your particular case is safe.

You'll also probably lose the RPM indication from the third wire, if you're using it. The ones I've seen are just open collector switches between ground and open/pull-up and the hack moves "ground" to 5V.

The grounds are bonded to the case and connected to the safety ground, so you will short out the supplies.

ATX PSUs connect the 0V (black) wires to the ground pin of the IEC power input connector, and the nmetal case.

connecting 12V directly to 5V or to 5V in another PSU will do noting good, the best you can expect is the machine to shut down, but it could cause permanent damage.

Why can't you unscrew the circuit board off the case-ie disconnect the black wire from ac input ground

non pc ps?

No. Even if you floated one of the supplies, putting switcher outputs in series is a Very Bad Idea, because they'll fight over who gets to regulate the output.

Don't even bother. Spring for the 24V supply.

Sorry. Rich

well if you unscrew the board /circuit gnd off the case ? I think each of ps will set their current to Vout.total/Load and regulate it's output?

Then it will not work properly. Also, if you try to isolate it, it will radiate a lot of RF and interfere with other equipment. it will violate the UL or similar certification, and can kill you.

In theory connecting voltage regulated supplies in series is fine.

the problem is that to make it work you'd have to effectively cut the earth wire, the earth wire is a safety device and disabling it increases the risk to anyone who encounters the equipment

For a test, OP could get one of those floater plugs (2 male prongs, a pigtail, and a 3-prong plug); float the whole supply, and do a lashup - I'd be surprised if the series supplies don't break into uncontrolled oscillations as they go in and out of overload and stuff.

Why not get the 2-prong adapter, lash it up on the bench, and report back?

(while doing this, of course the floated supply's chassis has to be insulated from _everything_.)

Good Luck! Rich

pc working just fine from 2 prong socket. The question is actually if say both 12v and 5 v are regulated do you have a proper error signal feeding the 2 small signal transfer functions

mynick wrote in news: snipped-for-privacy@y3g2000vbm.googlegroups.com :

If your looking for a 120W 50 to 60V o/p PSU just buy one heres one adjustable from 42-54V 3.3A MAX OUTPUT. Universal input TDK Supply.

Canadian distrubitor. $37

You could probably find one cheaper but you could trust this one more then say one off EBAY.

I salvaged a couple of computer power supplies and seriesed them. I dismounted each power supply's circuit board and insulated it from the case. I used the same insulating washers I mount TO-220 parts on heatsinks with. The power supplies can touch each other without shorting out, and I didn't have to change the plugs. On the few occasions I've actually used these power supplies in series, they have behaved well; no oscillations or faults. Call it a redneck power supply.

thanks I suppose there will not be any probs because it has kia494 votage mode pwm inside

for sake of argument would 2 ps fight each other if there was pwm (joint) current regulation in addition to voltages