Beginner: Need advice on ATX PSU > Bench PSU...

[Widget]

Hey guys,

new here and to electronics, was hoping for some feedback on my current project.

I have an old Antec 350w PSU sitting ehre and I want to turn it into a PSU that I can use for Electrolysis (rust removal). I have a general idea of what to do, but a few things seem to boggle me.

First, a few pics..





There's a bulging cap I was going to replace. The caps used are 'Fuhjyyu' brand.. which I read were rubbish.

Question: Do I need to keep the uF the same or can I go higher?

https://youtu.be/z2oSFpKh_Uw?list=FL...qhwKriX-qQLpoA

http://jumperone.com/2012/12/convert...supply-faq/#Q2

This is the one I'm (sort of) following. Though I wasn't planning on using the 3.3v.. probably just use the 5v and 12v connected to binding posts.

As for the dummy load, that's where I'm having some issues with. A couple of options I'm looking at are

1x led on the 5v (standby)
or
Using the psu fan (as suggested by a member in another forum), connecting it directly to a 12v wire and ground.

However, I'm wanting to use LED(s).. but.. I'm still a little uncertain on Resistors.

I had a look at the datasheet for some LEDs I'm considering getting, but am having trouble figuring out what specs/requirements they are..

http://pdf1.alldatasheet.com/datashe...GHT/L53HD.html

i think the above datasheet has details for all 3x LED's below ?

Kingbright L-53HD - 25mA max? (0.025 Amp)
Kingbright L-53ND - 30mA max? (0.030 Amp)
Kingbright L-53GD - 25mA max? (0.025 Amp)

According to RSOnline (where I'm looking to get from), they say

RED forward V = 2.25 V
Orange forward v = 2.05 V
Green forward V = 2 V

So, say I put the RED LED on the +5v Standby and I want to run 20mA (0.020 amps) through it.

RED LED has 2.25fV drop ? = 2.75v ?

R = V / I
R = 2.75 / 0.020
R = 135.5ohms ? will limit current to 20mA ? = ok to use on that LED ?

(orange R = 147.5)
(Green R = 150)

These are 133ohms,

http://au.rs-online.com/web/p/throug...stors/6833014/

which means

I = V / R
I = 2.75v / 133
I = 0.0206... ?

Is that right?

If so, that would mean the 133ohm resistors would still be ok for the orange and green LEDs (about 0.022A) ?

Appreciated any and all feedback

[stj]

Re: Beginner: Need advice on ATX PSU > Bench PSU...

led calculator
http://led.linear1.org/1led.wiz

[budm]

Re: Beginner: Need advice on ATX PSU > Bench PSU...

Do you know the spec of the expected minimum load for this power supply is for it to regulate properly?

[Widget]

Re: Beginner: Need advice on ATX PSU > Bench PSU...

Thanks stj . I had a look, and it's giving me a different resistance than my calculations.. is there something wrong with how I calculated the resistance from the above post?

Hi budm ... I'm not sure :/. Do you mean minimum load for the LED setup? or the amount (minimum) load connecting to the psu once complete?

At this stage, I hadn't planned to use it as a lab PSU for powering other electronics, rather a bit of a hands-on learning experience to make a power source for rust removal (electrolysis)

[fzabkar]

Re: Beginner: Need advice on ATX PSU > Bench PSU...

For electrolysis you need a current source, not a voltage source.

[sam_sam_sam]

Re: Beginner: Need advice on ATX PSU > Bench PSU...

Hey guys,



[URL=http://s998.photobucket.com/user/Widget1983/media/Electronics/IMG_20150725_205012_zpsj7grc5jy.jpg.html][IMG]http://i998.photobucket.com/albums/af101/Widget1983/Electronics

However, I'm wanting to use LED(s).. but.. I'm still a little uncertain on Resistors

[url]http://pdf1.alldatasheet.com/datasheet-pdf

Kingbright L-53HD - 25mA max? (0.025 Amp)
Kingbright L-53ND - 30mA max? (0.030 Amp)
Kingbright L-53GD - 25mA max? (0.025g Amp)

According to RSOnline (where I'm looking to get from), they say

RED forward V = 2.25 V
Orange forward v = 2.05 V
Green forward V = 2 V

So, say I put the RED LED on the +5v Standby and I want to run 20mA (0.020 amps) through it.

RED LED has 2.25fV drop ? = 2.75v ?

R = V / I
R = 2.75 / 0.020
R = 135.5ohms ? will limit current to 20mA ? = ok to use on that LED ?

(orange R = 147.5)
(Green R = 150)

These are 133ohms,

http://au.rs-online.com/web/p/throug...stors/6833014/

which means

I = V / R
I = 2.75v / 133
I = 0.0206... ?

Is that right?

If so, that would mean the 133ohm resistors would still be ok for the orange and green LEDs (about 0.022A) ?

Appreciated any and all feedback

If you want to be on the safe side you can use a one Kohm resistor for the voltage 3.3 to 12 volts with no problem
You could use A 130 ohm resistor but you would be drive the LED hard and it would not last long you could use a 330 ohm resistor which would a better choice for 3.3 volts

[Widget]

Re: Beginner: Need advice on ATX PSU > Bench PSU...

Thanks guys,

fzabkar: True, I was going to use the 12v source as from what I've read, 21A was more than enough for the items/size that I want to de-rust.

sam: not sure what you mean about the 1kohm for 3.3 to 12v?

With the LED resistors, I was going to go with 140ohm, but I wasn't sure of how bright a higher resistor would make the LED, so I went for closer to max.

I've ordered some LEDs/resistors so I might use some alligator clips to have a play when they get here. hopefully I ordered the correct ones...

[mariushm]

Re: Beginner: Need advice on ATX PSU > Bench PSU...

You don't need 20mA for leds. Modern leds will be super bright even at 10 mA. Some SuperBright red leds will leave a spot of red across the room with even 5mA.

You choose the resistor using the classic, plain, V = I x R but you have to keep in mind the forward voltage of the led which varies depending on the color.
Red/yellow/orange leds have forward voltage of about 1.8-2.2v, green, blue, white have about 3-3.2v forward voltage

So basically Vin - Vled = I x R ---> R = (Vin-Vled) / I

For 10mA (0.01A) and led with 3v forward voltage and 12v input voltage you have R = (12-3)/0.01 = 9/0.01 = 900 ohm. I'd just pick a 1000 ohm resistor and be satisfied with about 8-9mA going through the led.

The energy dissipated in the resistor will be P = I x I x R = 0.01x0.01x900 = 0.09w so a resistor rated for 0.125w will be sufficient.

[budm]

Re: Beginner: Need advice on ATX PSU > Bench PSU...

"fzabkar: True, I was going to use the 12v source as from what I've read, 21A was more than enough for the items/size that I want to de-rust." So you need 21A of current to flow for it to work, but the amount of current depends on the load resistance but since the load resistance will vary so to maintain 21A to flow then you will need constant current source.
12V @21A that is a very low resistance.