This is my first instructable and when i originally made this project i had not intended to make an instructable out of it , so there are far less pictures of it disassembled than i hoped , also google photos managed to reduce the quality of said images from 1080p to i can see each individual pixel on screen , so i apologize if you can't make something out , feel free to ask.
A lab bench power supply is the most essential tool for testing/ working on electronics. Although it is possible to get by with an atx power supply's 3 ,5 and 12 volt outputs for most circuits , it's unimaginably better when you can set any voltage output you may desire. Most simple (beginner friendly) variable lab bench power supply designs revolve around the lm 317/338 (1A/5A max output) and a voltage/current display module for viewing the output. The problem with these is that you don't have fine control over the voltage , and if you wanted to add a constant current mode above 1A you'd find that it's impossible to do , since running the lm 317/338 in CC mode requires a resistor (or a pot for variable output) strong enough to take the full current. Running the circuit at the lm338's max output of 5 amps at a voltage of mere 3 volts would require a 15 watt pot , not an easy find (nor cheap for that matter) . Lab bench PSUs with the features above can be made at home but require advanced skills in electronics , since most designs utilize some form of a switching circuit whether it's opamp , arduino or even premade IC based and are not recommended for beginners since most don't have the necessary tools at home. To design a switching circuit one MUST have a variable psu to begin with and an oscilloscope , preferably even a signal generator. So , how can a newbie with almost no gear and little skills apart from how to solder , make themselves a professional looking lab bench psu with all the bells and whistles....? Enter the DPS3005 , china's solution to our problem. Costing a mere 23EUR , it's a full blown switchmode power supply with an integrated display and controls. The module takes in DC power at a maximum of 40 volts and outputs voltages in a range of 0-32 volts at a maximum of 5 amps.
Step 1: Parts List and Links
The links provided are from aliexpress , i'm certain you can find the same parts on ebay. The reason i call this project noob friendly is because no parts are picked using a calculation or any sort of engineering prowess , except for the module itself ( even though the other models have similar if not better specifications , they can be a lot more expensive though) , every other part is picked by what will suit you , what you can afford , what you need for your application eg. you can use a much weaker transformer if you don't need 60 watts , or you can get up to a 40 volt 5 amp one if you can find.
1. Project box (use whatever you can get for cheap , materials don't matter since this thing runs pretty cool , esp. when using a fan)
here's a good example
As said above if you need more power / less space , you can get a bigger / smaller transformer , as long as its at least 12 volts on the output. You can even use a laptop charger if you want to make your lab psu extremely portable.
3.The DPS3005 module
IF you have the knowledge , there are more expensive and powerful versions of this which even have serial communication
Here's a link for an 8A 1000V rectifier. This is way overkill but it's also way above the max rating of the module.
5. Smoothing cap (not in picture)
The instructions for the module recommend a 4700uf min smoothing capacitor if powered by a transformer
6. Binding posts (not in picture)
I got mine from the same store i got the box from , but these look good too
7. Fuse (not in picture)
I couldn't find a fuse with a small enough value on aliexpress , the fuse is only there to blow in case of a short and not have your main house circuit breaker trip , so 250V 1 amp is enough , also get a holder that can be mounted on a case
8. Switch (not in picture)
Use any switch you can find laying around that can handle 250V ac at more than an amp , basically any switch you find. I used a rocker , like this , but you can also use any type of switch.
Optionally you can a heatsink for the rectifier , though it is not necessary for proper operation
Also if you intend on installing a fan using nuts and bolts like i did , you can get a bag of nuts and bolts from your local hardware store
Step 2: Assembly
I apologize in advance but when i was making this project originally almost a year ago i never intended to make an instructable so i have very few assembly pictures , ill try to do my best in explaining , on the pictures i have put in i have added notes explaining how to wire things , feel free to ask in comments for any particular step
For cutting the plastic i used a dremel with a cutting disc and a drill bit.
And if you don't intend to install a fan , congratulations , you just made yourself an amazing lab bench power supply. IF you wish to add a fan , go to the next step.
A fairly odd quirk i've discovered is that even after experimenting with capacitor values , it still reads 18 volts on input and it allows and output of 17 volts , though this drops off as you put a load on it.
Step 3: Fan Circuit
I decided on a simple 555 timer pwm circuit since when using a discrete transistor oscillator i ran into various problems which caused the oscillating to stop or slow down. The actual values i used are possibly different from the ones in the schematic , but i don't remember them. The beauty of the 555 oscillator is that it is such a widespread circuit that there exist online services and even phone apps that will calculate resistor values for you , just from the frequency and duty cycle you require. One set of values that gives us a good frequency for pwm and a good range of fan speeds is the one in the schematic. You can also find your own values based on parts you can find at home.
If you cannot read the values in the picture they are 1k thermistor , 1k resistor , 1n capacitor and 0.1u capacitor between pin 5 and GND