ATX power supply conversion to lab not working

[carpj]

Any suggestions.....

I have converted a Turbo Link ATX Switching Power Supply with 20 pin connector, Model No: WIN-350PS with AC INPUT 115/230V & DC OUTPUT: 350W to a lab power supply. I joined wires black gnd red +5v white -5v yellow +12v blue -12v orange +3v. Installed green wire to switch to gnd. Placed 10w 10o on red & black wires to use up power as per online instructions. I also wired in LED grey to black with resister.

When I start it up we get 1-2 fan and LED lit then everything goes into safe mode until I switch it off for a few minutes. The only time I can get it to run continuous is buy hooking up an old floppy drive first.

Absolutely stumped on how to fix this properly. Have tried different wiring arrangements and nothing seems to work.

Any ideas or help would be much appreciated.

Jeff

[selldoor]

Re: ATX power supply conversion to lab not working

You have more or less answered your own question.
Some ATX PSUs have to have a 5v load for them to run.
There are many articles on this subject - some in these forums.
Most people seem to fit lamps, less intrusive than a floppy drive.

Just type ATX dummy load into google.

[carpj]

Re: ATX power supply conversion to lab not working

Thanks Selldoor for your reply. Can I use a 10w 10olm resister to play the role of a lamp? 2nd... do I hook this lamp to black & red?

[momaka]

Re: ATX power supply conversion to lab not working

Can you post a picture of the inside of the power supply?

Reason I ask is because I also have two TurboLink/Cyberlink power supplies (both are low-end CWT-made units) and they have no problem powering on without ANY load attached.

If your Turbolink came from a heavily-used computer, the caps in it might have started to go (or are) bad.

[carpj]

Re: ATX power supply conversion to lab not working

Hi Momaka, I do not think my caps are on the way out. When yellow and black wires are hooked up to floppy drive I can get continuous power to PS fans. Here are the sticker & inside photos. Any insight would be great. On another note.... a 10W 10olm resister with 12v load will run PS for about 90 seconds before cutting out. The resister gets really hot before cut-out. This cut-out does not happen when hooked up to floppy drive.

Thanks Jeff

[mariushm]

Re: ATX power supply conversion to lab not working

Those designs of power supplies need minimum loads on the outputs to work properly.

About 1-2 watts on each (3.3v, 5v, 12v) would probably be enough.
You can use ohm's law to determine what resistor to use
V= I x R
and the formula Power (watts) = I x I x R

A trick you could do would be to get a cheap boost regulator from ebay (they're a few dollars) and boost 5v to 12v or thereabouts and connect the fan of the power supply to that 12v. The fan should use enough power to stabilize the outputs. If you don't want to buy from eBay, you can make your own using a MC34063 IC, there's plenty of circuits and online calculators for the parts needed besides the IC out there.

[carpj]

Re: ATX power supply conversion to lab not working

Hi mariushm,

Thanks for the input. I guess I have to duplicate the power being used by the floppy drive. Can I use a 10w 10olm for +5v and what would u recommend for the 12v ? What about lamps? Any idea how I might get these to work?

PS the things I do for my sons education! :P

[mariushm]

Re: ATX power supply conversion to lab not working

Well do the math, man...
v = i x r .. 5v = i x 10 ohm => i = 5/10 = 0.5A ..
p = i x i x r = 0.5x0.5x10 = 2.5 watts.

So could you use a 10 ohm 10w resistor? Yeah, 2.5w is less than 10w so it should be fine.
Should you use use? I would not use it unless you will keep the fan running, 2.5w is probably too much wasted power as heat.

That is a shitty power supply.. it will output the voltages just fine but it's crappy.

I don't know what you mean by "the things I do for my sons education! :P"

If you do it to teach your son something, or you try to learn something, I'd suggest you build a plain linear power supply, using a regular transformer, linear regulators etc.
You'll learn more from the process and overall, the power supply will be SAFER.
These switching power supplies use high voltage (up to 350-400v) on the primary side which can be dangerous, especially since it seems like you're going to have cables going to those terminals sitting over those tiny heatsinks.

Lamps are simple resistors, but they change the resistance slightly as they heat up and go incandescent. Should you use it... I don't know, lamps are very inneficient, only a few percents of power goes as light, rest goes as heat. So you basically get the same result... however, lamps are a bit hard to find as 1w, 2w lamps... if you use 5v 10w or 12v 10w lamps, they'll do too much heat inside the power supply.

[momaka]

Re: ATX power supply conversion to lab not working

Hi Momaka, I do not think my caps are on the way out.

Have a look at your second picture. There's one cap under a white wire (lower center of the photo). I'm not sure if that's just from the picture or not, but to me that cap appears a bit bulged. Look at it carefully and let me know what you find.

If it's not, then you just need a proper load as mariushm mentioned. I would discourage using load resistors only because large ones rated for over 5W can get expensive and may be hard to find locally. In my experience 12V halogen incandescent lamps (like the ones sold in Ikea for track lights) have worked fine. Or you can also go to an auto parts store and get some headlight / taillight / dome lights.

If you go with the 12V halogen lamps, 20W to 30W should be fine (easy to find too). Put one on each of the main rails - that is, have one lamp on 12V rail, one on 5V rail, and one on 3.3V rail.

Or if you get headlight / taillight / dome lights, something around 5 to 10W should be okay. Again, put one on each of the main rails.

As mariushm mentioned, you would probably have to have those mounted outside of the case because they do generate some heat.

And oh yes, I forgot to mention, but your Turbolink appears different from mine. I think yours is made by Wintech.

[carpj]

Re: ATX power supply conversion to lab not working

mariushm,

Again.... thanks for your input. My PS was free (old PC) and many people are using these power supplies to create a lab power source. The 10w 10 ohm resister was chosen as per an online conversion I found. With lots of different kinds of ATX PS's out there I needed more input for my PS mod.

I do not know anything about plain linear PS. Just trying to create a Lab PS for my son's mechanical electrical engineering technician collage course he just started.

My 10W 10 ohm resister has way to much heat to be part of a +12v rail and shuts down the PS when the heat reaches a certain level. What I need is a way to re-create my floppy drives power usage of +5v rail & +12v rail & fit it into the case.

If the bulbs burn too much heat I will be no further ahead than my 10w resister. Would this resister be better on the +5v rail instead of the +12v rail? Then all I need would be a resister or bulb for the +12v rail. Will that work with my free PS?

[mariushm]

Re: ATX power supply conversion to lab not working

Repeat the computations for 12v ...

v = i x r ... i = v /r = 12v/10ohm = 1.2 a
p = i x i x r = 1.2 x 1.2 x 10 = 14.4w

How do you think you would dissipate 14.4 watts using a 10w rated resistor? The resistor probably overheats and causes a short which makes the power supply shut down.

You can use a multimeter to measure the current drawn by that floppy disk. Cut the red wire somewhere, put the multimeter in between the wires, start the power supply and measure the current. You get the current for 5v (red is 5v) Repeat with the yellow wire which is 12 volts.

My prediction is that the floppy disk is using about 0.2A on 5v and barely uses 12v, maybe when spinning the drive to search for a floppy disk inside.

Again, such a power supply doesn't need large loads, i already told you about 1w on all rails is enough. Your 10 ohm resistor is already pulling 2.5watts from the 5v, so my recommendation would be to use larger resistors.

100-220 ohm for 12v should be enough... a 100 ohm resistor will waste about 1.4 watts as heat, so a 3w rated resistor will be barely suitable (it will be HOT but not burn out)

[carpj]

Re: ATX power supply conversion to lab not working

mariushm,

I know talking to electrical newbys can be a little frustrating, so I appreciate the effort.

If I use my 10w 10ohm resister on the +5v rail and a 200ohm resister on the +12v rail, do u think this will give continuous power to allow circuit testing on the 3 way posts for +5v -5v +12v & -12v ? And if this will work will these resisters have too much heat inside the case even with the PS fan functioning. Should I just go with 200ohm 3w on both +5v & +12v rails? +3v rail with be unused should not need a load (I hope).

The PS lid has grill covered opening for 2nd fan (but no room for 2nd fan & mods).

Jeff

[carpj]

Re: ATX power supply conversion to lab not working

momaka,

Yes a bulge in a cap would spell the end of that cap. The cap your looking at in the pic with the white wire above it is fine. If you zoom in to the photo the cap looks perfectly fine.

But I do appreciate the heads up. If the cap were blown I would scrap the PS and just use another one from my stock pile of old PC's.

Gotta Love This Site

Jeff

[carpj]

Re: ATX power supply conversion to lab not working

Update..... I was finally able to get the power supply working without the floppy drive hookup. I tested several 12V car bulbs until I had 2 that would keep the power on. First single element bulb was soldered to the 12V rail & 2nd single element car bulb was soldered to the 5V rail. I did not intend to use the 3V rail & did not need to attach any resister to it.

Thanks for all your ideas to a Newby...... mission accomplished!

Here is the finished result.

[momaka]

Re: ATX power supply conversion to lab not working

Looks good, but have you tried measuring the output voltages?
The fact that the PSU is picky about the bulbs tells me something is not right with its feedback circuit or the caps (even though they look good).
Also, just because you're not going to use 3.3V rail doesn't mean you shouldn't put some load on it. The PSU looks at the voltage on all rails, and if one is way too high, it will lower the power output, thus causing the voltage to be lowered on other rails too.
Also, 3.3V is actually useful to have. It's close to the voltage of 2 AA batteries in series. So if your son decides to test a device that otherwise uses 2 AA batteries in series, he can use the PSU.

[domas]

Re: ATX power supply conversion to lab not working

nice.

i hate wasting power with load resistors, but sometimes you do what you have to do.
BTW, weren’t there any resistors present on 5v and 12V rails in the PSU? I had one on 5V minimal IIRC. And I needed both, for 12V and for 5V, so I added one for 12V, and desoldered the 5V resistor. Moved both to a heatsink, as they are general-purpose resistors (I assume like 3-5W), therefore I heatsinked them with thermal paste to a chipset heatsink, then I have just attached the new heatsink to the output rectifier sink. Ghetto, but does the job.
The psu did not need 12V load before the conversion, but I had to reconnect the fan to 10V stby rail, as I made my 12V rail adjustable.

[carpj]

Re: ATX power supply conversion to lab not working

This site has amazed me with the help I have received for my son's PC PSU to Lab PSU. As I do not possess the knowledge of electronics nor the formulas to understand what actually works, I instead went with the "lets see what does work" theme.

Momaka, I did measure the output leads. 5V rail were very close on both + & - The -12V rail was sitting around -11.45 -11.6 The +12V rail was a little high +13.5 13.87 The reason I did not hook up the +3V rail was due to my son not needing it in his testing. I can still drill a hole and hook it up if his requirements change.

I did however use insulated wire to wire the bulbs to the main cap heat sink to allow faster heat dissipation of 12V rail, bulb. I also used a metal shield to partially obscure the bulb from blinding anyone when in operation. (bulbs shines thru top grilled opening).

Jeff
London Ontario

[momaka]

Re: ATX power supply conversion to lab not working

The +12V rail was a little high +13.5 13.87

Little high is an understatement - it's well outside of ATX spec (which only allows 11.4 to 12.6V). Good thing that PSU is no longer in a computer. Even without load, the 12V rail voltage shouldn't got that high.

[senz_90]

Re: ATX power supply conversion to lab not working

yeah. it should not be those high.. negative rails has a 10% tolerance, positive rails has a 5% tolerance of the voltages.

it should better if you can attach the bulb on the outside of PSU, because the bulb produces heat, not same as led produces a very small heat.

btw good work !! keep moving

[cheapie]

Re: ATX power supply conversion to lab not working

it should better if you can attach the bulb on the outside of PSU, because the bulb produces heat, not same as led produces a very small heat.

But it looks cooler on the inside! Maybe he should have used blue light bulbs though.