Chinese power supply LM317 overheating.

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

NMF, it's been a long time since I last looked at the current waveform for a DC fan, so I'm afraid I can't be helpful.

Yes, I do mean a hefty heatsink is usually a good thing, in proportion to the device(s) mounted on the heatsink.

Maybe the dust from the past drought years got a little moisture from last winter's rains.

IIRC, older ATX PSUs had ~6A 12V outputs. A ~2A load on the 5V output might be enough to have the 12V output close to in regulation. Got any ancient junker ATX PSUs packratted away?

Yes. I am trying to research what resistor to use on an old ATX PSU.

Here's the link if you have any experience with them.:
https://www.badcaps.net/forum/showthread.php?t=65913

[mariushm]

Re: Chinese power supply LM317 overheating.

I wonder why don't you make your own power supply for those 12v fans?

For fans, you don't even need super high regulation, you just need to make sure the voltage won't go over around 13v - the fans will work from something like 5v all the way up to 13.2v DC (as required by ATX standard)

So for example, you could get a transformer that outputs 10v AC and after rectification using a bridge rectifier you'd get around 13-14v DC, so you can use a plain linear regulator like LM1085 (3A regulator with <1v voltage drop) to get around 11v..12v ... like I said, you don't need exactly 12v for fans.

If you want precise 12v, you'd want at least 12v AC or better, around 15v AC because after rectification you have some losses.

Peak DC voltage after rectification = Vac x 1.414 - 2 x voltage drop on one diode in bridge rectifier

So 15v AC x 1.414 - 2 x ~ 1v = ~ 19v DC

You need capacitor to raise the minimum voltage to the minimum value you want, let's say 14v DC so that your linear regulator will output 12v in any condition

Capacitance (in Farads) = Current / [ 2 x mains frequency in Hz x (Vdc peak - Vdc min) ]

So for 2A , you'd have C = 2 / 2 x 60Hz x (19 - 14) = 2 / 120x 5 = 0.0033333 Farads or 3333 uF

So a 3300 uF 25v capacitor would be enough to keep DC voltage between 14v .. 19v up to 2A of current, and the linear regulator would be happy and output 2A of current.
Note that the regulator outputs the difference between input voltage and output voltage as heat, so it needs some heatsink. Without any heatsink, the TO-220 is good for up to maybe 2w of dissipated heat.

For example, let's say at 1A of current you'd have an average of 16v on the regulator.. then the regulator outputs (16v-12v)x1a = 4w of heat... those must go on a heatsink.


LM1085 adjustable ( up to 29v input, 1.25v .. 15v output, 3A , 1.5v dropout at 3A) : https://www.digikey.com/product-deta...NOPB-ND/363565

For 2A of current at 12v, you'd need a transformer rated for more than 25VA

If you want to go with a 10v AC transformer , here's a good example of a cheap one:

11.5$ 20VA 10v or 20v AC (two windings, connect in parallel for 10v and 2A) https://www.digikey.com/product-deta...1070-ND/242514

You rectify this to DC using a bridge rectifier and you'll get up to 12-15v DC depending on load. Add a 3300uF or more and you have 12v or more pretty much all the time.
Add a linear regulator configured for 12v and then you'll have voltage somewhere around 11v..12v all the time. If you set a regulator to 12v and input voltage is less than output voltage + dropout voltage, the regulator will output less than 12v but it will still output, it won't turn off.

A couple more dollars gets you a proper 12v AC transformer and a 30VA rating so with this one you can be pretty sure you always get more than 12v DC:

14.5 30VA 12v or 24v AC (two windings) https://www.digikey.com/product-deta...1078-ND/242522


-

Another option for a home project would be to repurpose a 12v laptop adapter or 16.5v / 18v laptop adapter, you can buy some of those

Or 15.5$ gets you a whole 12v 35w power supply from Delta: https://www.digikey.com/product-deta...072-ND/4386543

Or even cheaper at 11.5$ you can get a 25w 12v wall wart style adapter: https://www.digikey.com/product-deta...197-ND/7070093
Just install a barrel jack on your cable that gives power to all the fans or your fan controller and you just plug the wall wart adapter into the mains socket.

[budm]

Re: Chinese power supply LM317 overheating.

12VDC 3A wall-wart is cheap! If you have electronics re-cycler place close by they should have lots of them.

[stj]

Re: Chinese power supply LM317 overheating.

wall units are rubish, best would be a 3a-5a psu from an lcd tv / monitor.
(better build quality)

[budm]

Re: Chinese power supply LM317 overheating.

Rubbish compared to crappy Philips TV with 2-Transistor switching power supply and other TV power supplies that failed with bad caps?
It is just for the Fans, not mission critical.

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

Interesting. I've gotta install some plugs in the kitchen and fix a washing machine. But then I'm gonna reread your comment to comprehend the math better.

I looked through my resistors(to make my atx-300 stay on) I have some that are close. I'll try them after I get done with more important stuff.

And I'll take another look in my AC adapter box. I think I have one that went to a printer. But I think that one can only do 1.5amps. it also does 22v and I think 5v. The plug looks like an old s-video(?) cable that plugs into a tv.

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

wall units are rubish, best would be a 3a-5a psu from an lcd tv / monitor.
(better build quality)

Interesting. I took apart an old dell monitor. It had a rather large power supply board. I might take a look at that and play with it, just to see what voltages it puts out.

But at the moment I have more than 5 cpu PSUs.

[budm]

Re: Chinese power supply LM317 overheating.

You can use 6V 10W lamp to load the 5V supply in stead of wasting heat using resistor, you get the working lights at the same time.

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

Rubbish compared to crappy Philips TV with 2-Transistor switching power supply and other TV power supplies that failed with bad caps?
It is just for the Fans, not mission critical.

Yah. Just for the fans. though I always end up adding other crap. I had led strips lighting up my keyboard and desktop for a while, but I took it down. I don't know if it was he color frequency or the frequency of the pulses of the leds that bothered my eyes. I had that 12v ebay LED strip powered straight from my CPUs PSU. If I had it powered off the bench power supply there would probably be no flicker. But I got that bench power supply years later.

[NeedsMoreFlux]

Re: Chinese power supply LM317 overheating.

You can use 6V 10W lamp to load the 5V supply in stead of wasting heat using resistor, you get the working lights at the same time.

Hmmm... I've been thinking about that.

I wonder if I could make some connectors so that I can unplug it and put an extension on it. It probably wouldn't blow up. plus that'd give me more light to work on electronics. I like it.

I did make a 24volt tester with 2x12v halogens-after reading your tv troubleshooting manual.

[stj]

Re: Chinese power supply LM317 overheating.

i was talking about EXTERNAL power supplies - not the pfc crippled crap they build into them now.