0x03 NTTF - a PSU mod

davedarkodavedarko wrote 01/25/2015 at 22:42 • 4 min read • Like

My usual way to power something with 5V? An old cell phone power supply. My usual way to power something with 3.3V? An old cell phone power supply, connected to a 3.3V arduino micro. That has to stop, so I asked my dad for an old power supply he surely had laying around and ordered some parts on the usual places. The plan is to use the 12V, 5V and 3.3V as seen before on so many places. Additionally, there will be a variable output controlled by a LM2595(ebay) with a LED display voltage meter (ebay). Now I just have to wait for the copper chicken head knob for the 10k resistor and the resistor itself, but nothing that should hold me from starting, though. *While writing thinking edit*: I need those min load capacitors. Sounds like some really tough math to get involved to.

\color{White} \large R_{3.3} = 3.3V/1A = 3.3 \Omega

\color{White} \large R_{5} = 5V/1A = 5 \Omega

\color{White} \large R_{12} = 12V/1A = 12 \Omega

No such things as 5 ohm I could find, so I'm looking for 4.7 ohms.

\color{White} \large I = 5V / 4.7 \Omega = 1.07A

Yeah, I just wanted to play with the latex feature, I admit it :D Next on is the wattage.

\color{White} \large P_{3.3} = 3.3V*1A = 3.3W

\color{White} \large P_{5} = 5V*1.07A = 5.35W

\color{White} \large P_{12} = 12V*1A = 12W

I ended up buying LSR-120/20, LSR-33/10 and LSR-47/10, they are not the cheapest, but I could get them all from one seller and hope on some combined shipping costs, thanks ebay, for finally making this possible. I'll use some plywood to place the ports, the display, power good led and the potentiometer - and should not forget the switch.

Well, so much for planning, not the best page I wrote, but it's supposed to be more a log this time - a note to the future me. That's why I gave it the title. Why do I explain something self-explaining? I'm tired.

#ATX Benchtop Power Supply - quite nice instructions, but don't cross the streams like he did!

#Bench Power Supply - ATX PSU Adapter - he can even reuse his PSU or change it for another!

#ATX power supply conversion for bench usage - the reason why I won't make a project out of it - the third great write up :)



Eric Hertz wrote 01/26/2015 at 00:35 point

Not to discourage... but I built a power-supply similar to this long ago... I use it when needing a variable voltage or a lot of power or when doing unusual experiments. But, really, old cell-phone "wall-warts" are so small and convenient for most of my projects that my power-supply often sits in a box (actually, I looked for it the other day and don't even know where it is!).

It seems like going backwards, but the power-supply I use the most is an old cable-modem wall-wart which output 5V and 12V, throwing a variable-regulator (usually set to 3.3V) in a small box with a bunch of color-coded wires hanging out with already-attached power-connectors (e.g. 0.1in spacing, 2-pin). It's a bit of a power-octopus, but barely takes up any space and already has most of the connectors I need.

OTOH, I'm a bit short on workspace... But, yeah, a PSU like you're building is a great tool to have around, and you'll probably be using it for projects for years to come. (Building tools is almost more-rewarding than building projects with them :)

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davedarko wrote 01/26/2015 at 09:51 point

I know what you mean, but this will be installed "into" my soldering/hacking dedicated desk, so I think I will use it out of convenience. And building tools is awesome and rewarding, indeed!

sometimes I notice that I keep my english fresh by watching stargate :D

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zakqwy wrote 01/26/2015 at 00:06 point

Nice! Yeah, remember--non-isolated! :-/

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davedarko wrote 01/26/2015 at 09:47 point

I just figured that some one could think I meant "cross the voltage streams". I hope I will be careful with it :) And if not, I have a second power supply ready.

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