Compact Regulated PSU - Power Supply Unit

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I have already make a few PSU. At the beginning I always assumed that I need PSU with lots of Amps, but during few years of experimenting and building things I realized that i need small compact PSU with stabilize and good Voltage regulation and current limiter, that didn't take to much space on my workbench.

Like in most of my project it all started with salvage components that came in my possession.
Friend of mine gave my transformer 230V/16V from the old alarm system which is the main component of mine PSU.

Step 1: Component List

1. Transformator 230V/16 V - 1,8 A

2. Original Hiland 0-30V 2mA - 3A Adjustable DC Regulated Power Supply DIY Kit

https://www.banggood.com/0-30V-2mA-3A-Adjustable-D...

3. Dual Red Blue LED Digital Voltmeter Ammeter Panel Volt Gauge Meter

https://www.banggood.com/Dual-Red-Blue-LED-Digital...

4. DC 12V -50 to +110 Temperature Control Switch Thermostat Thermometer

https://www.banggood.com/DC-12V-50-to-110-Temperat...

5. Heat sink with fan (24VDC)

6.Voltage stabilization IC 7812

7. Lot 3MM Silver Chrome Metal Plastic LED Light Lamp Emitting Diode Bezel Holders

https://www.banggood.com/Lot-3MM-Silver-Chrome-Met...

8. 3 x LED 3mm

9. 2 x Pot. knob

https://www.banggood.com/Potentiometer-Volume-Cont...

10. ATX shell

11. 24VAC power relay with 4 contact (NO-COM-NC) this is option for WELLER supply compatibility

12. Vinyl Wrap Roll

https://www.banggood.com/200x40cm-DIY-Carbon-Fiber...

Step 2: ​ATX Housing Adaptation – Hardware Work

When I had all components at my hand it was time for space management inside of the PSU. Because I decided to use ATX power supply housing I have to manage everything very carefully and this space planning took me lot of time.

After everything was cool, I made a front label on my PC for easier marking.

Mostly it was just drilling, the hole for ampere/volt-meter I used small drill (don’t know how it is called)

At the bottom of the housing I have mounted four of stands that I demounted from old coffee maker

Handle on the back is from the old kitchen socket, mounted with two M4 nuts with washers :)

Step 3: Schematic

Here is schematic of the PSU (I’m not that skilled with drawing of the schematic, as you can see). If something is not clear please feel free to ask in comments, I’m realize that schematic could be done better and when I find some time I will upload better version.

I add thermostat for activating fan, when I use PSU on small current or on standby I don’t want to hear fan.
I have mounted transistor and voltage stabilization IC (7812), on the cooler.

I drilled hole for the thermostat probe into the cooler.

For mounting of the fan on the cooler I used 1.5mm copper wire and for fixing the fan and cooler onto the housing I used four 1cm standoffs.

Resistors for the LEDs are soldered directly on the 3mm LED and then isolated with shrinking tube.

Same principle is used for connecting the relays contacts

Step 4: Carbon Fibre Vinyl Wrap

I wanted to make a nice look for the housing, so I used Carbon Fiber Vinyl Wrap instead of painting. Also I got an idea that I could customize PSU with my signature :), I have cut my brand mark from the carton box and covered it with vinyl wrap, also I didn’t want to have unnecessary holes on the housing so I used carton box from my favorite cookies and cover the holes and also covered with vinyl wrap

Step 5: ​Front and Back Sticker

I wanted to have clear front panel, so I have design front panel on my computer (use which ever program you prefer) and printed out on printer. This is very convenient also for hardware part of drilling and cutting. Front of the sticker I have adhibit with see-through tape. Back of the sticker is adhibit with two-side tape and taped on the housing.

Step 6: Mounting Components on Front Panel and in the Housing

When the housing were prepared I have started with mounting the elements on/in it. Housing consist of two parts, so for easy assembling there should be long enough wires for manipulation during the assembly.

Grounding the housing is very import, ATX usually have a ground connecting place inside the housing, check it on the photos

First I have mounted everything in the housing and start wiring everything together according the schematic. All of contacts are well soldered creating good and reliable contact and isolated with shrinking tube insulators.

Step 7: ​Calibration and Setting of the Thermostat

Amper/Volt meter have a small potentiometer (miniature) on the back of the panel meter, used for calibration.

After wiring everything all together calibration of the volt meter and ampere meter was necessary. With Volt meter is quite easy and accurate, I have low the voltage to the 4.5V and use the potentiometer on the back of the voltmeter to set it with my multimeter, I repeat this at 12V and 13.7V.

Calibration of the Ampere meter was little bit tricky, I have calculate current for the 5W bulb P=U*I , so that current should be at 12V I=5 / 12 = 0.416A . This is not first class ampermeter but I manage to set it nearest to the desired value, I repeat this step with 15W and 21W bulb and manage to calibrated to the nearest values, and compare this with my multimeter and it is precisely enough for normal and reliable use. Do not expect lab PSU precisely values….

Thermostat is set to activate fan at 40 C°, setting the thermostat is not very complicated and the precise instruction are on the site where I bought the thermostat. After two months of using is working ok.

Step 8: ​Interconnecting Cable for Weller Soldering Station

I have TCP-S Weller soldering station which have 50W /24VAC transformer what is perfect for my PSU. From old Weller handle I have harvested connector and made Interconnecting cable suitable for my PSU in case if I need more Voltage and juice.

As you can see on the schematic, for this purpose I have add 24VAC relay on the input, when the external source is added PSU automatically switch to this input what is signalized with blue LED on the front panel.

Step 9: ​Final Product

It is nice PSU with small dimension, it is working fine and I am very pleased with it. Any suggestion and improvements are welcomed.

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    57 Discussions

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    AroAro

    4 months ago

    Hello,
    what will happen if you have set 3 A current and there is a short circuit without you noticing?
    At the transistor on the heat sink then fall almost 100 watts!

    Far too much for heatsinks and fans. The warm air remains partly in the housing and is sucked in again! You absolutely have to prevent that!
    The transistor will go defective.
    After that, much more will be broken.
    Preferably use the temperature monitoring to switch off the output when overheating!

    The supplied potentiometers are not suitable. 10-turn potentiometers are not expensive and much better to use.

    2 replies
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    medzikAroAro

    Reply 4 months ago

    Hello,

    Thanks for heads up, you are right about short circuit but actually the circuit have overload and short circuit protection, maybe 3A quick fuse on the output terminal will be good backup solution.

    Overheating is so far not a problem but I guess that depends on application , I mainly use the PSU for testing arduino DIY projects, when I need more juice for motors and similar I have PC power supply adapted like PSU.

    Biger heatsink and fan would ceartely be a better solution but then PSU would lost it compact size.

    About potentiometers, I dont think that multi rotation potentiometers are better solution for this low cost project. Sometimes it is really annoying turning knob from 5V to 24V.... And as the second argument, this PSU is made from scratch and two quality 10-turn potentiometers would be more expensive than entire project.

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    AroAromedzik

    Reply 4 months ago

    Hello,
    the short circuit is actually just the most obvious problem. For
    example, if you remove 3A at a voltage of 0.5 or 1 volt, then you have
    just 1.5 or 3 watts less power dissipation than with a short circuit! That's the problem with this circuit and almost nobody thinks about it.

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    Mack937Y

    Question 8 months ago on Step 9

    I thought while recouperating from shoulder surgery would be good time to finish psu. I've decided it's beyond my abilities. Mr Medzic you gave excellent help and it is my lack of specific knowledge for this was on me. So I put my psu away till I figure out what to do? Thank You Sir

    1 more answer
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    medzikMack937Y

    Answer 8 months ago

    I'm sorry to hear that, If you find time to complete PSU, I will be glad to help as much as possible

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    Mack937Y

    8 months ago

    I believe BG sold different revisions of the board. Notice where on above picture of board the (7824) markedb8,11,and 7. See on my version that it has been shifted as shown circled My question NOW is which pins are 8,11,7 and do I keep the 7824 mounted on board?

    image.jpeg
    1 reply
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    Mack937YMack937Y

    Reply 8 months ago

    I should have a few 7812 in hand by end of this week

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    Mack937Y

    Question 8 months ago

    On IC 7812. Which is "pin" #12 ?

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    Mack937Y

    Question 8 months ago on Step 3

    The diy power supply kit Version i received does NOT have pins 7,8,or 11 as shown above. And I'm in a quandary as to where I connect the front panel mounted led's. I am not installing the relay for a weller soldering option.

    Also the temperature control switch couple questions 1) where do I get 12v to power it , 2) what are K0 and K1? My fan is 24v

    image.jpeg
    5 more answers
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    medzikMack937Y

    Answer 8 months ago

    I hope that picture will help, you need to replace 7824 with 7812 . Or if there is higher voltage from the output of transformer ad 7812 parallel to the 7824. 78xx are voltage stabilizer , they had input, ground, and stabilized output.

    answer question.jpg
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    Mack937YMack937Y

    Answer 8 months ago

    hopefully the ones I uploaded are in the same orientation as your graphic

    image.jpegimage.jpeg
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    medzikMack937Y

    Answer 8 months ago

    Hello

    can you please post the picture of the pcb board from the kit so that I could figure it out other options.

    For the temperature switch use 12 from IC 7812 in schematic, for supply take the 24V from pcb point 9 and 10 , KO and K1 are the outputs of the relay (from point 9 go to K0 and from K1 to the fan)

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    KetkA

    1 year ago

    Hello. What a kind of sticker software did you use to do these front and
    back stickers? I have not idea about what a software use. Thanks. I wait your answer.

    5 replies
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    medzikKetkA

    Reply 1 year ago

    Hello, I used AutoCad

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    Mack937Ymedzik

    Reply 10 months ago

    Do you still have file saved on auto cad?

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    medzikMack937Y

    Reply 10 months ago

    Hi , I have uploaded pdf file in the step 5, autocad file is on my other PC , I will added it ASAP. Hope it will help

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    Mack937Ymedzik

    Reply 10 months ago

    I printed up my first face label but it's too small. It measures 2"x4 7/8". When it should be 3"x5 1/2". Cannot figure how make actuall size needed

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    medzikMack937Y

    Reply 10 months ago

    it is a little bit tricky, I'm doing it thru printing in pdf file, select the measurement 1:1,(if you have used inchs than leave it in inchs). After Christmas I could make printscreen.