Variable Lab Bench Power Supply!

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About: I'm a curious creator, fascinated by the combination of 3D printing and electronics.

Have you ever been creating your new project and held back by you lack of control over your power source? Well this is the project for you! Today I'll be showing you how to make an amazing lab bench power supply for very cheap! I made this whole thing for about $25 AUD and it looks and works great!

Step 1: Parts!!!

I'm listing all items on aliexpress due to it being worldwide however it's only a guide, as long as the values are similar you should be fine!

1- Audio Speaker Banana Plug

http://s.aliexpress.com/Mjy6nIb6?fromSns=

2- Mini Digital Voltmeter Ammeter DC

http://s.aliexpress.com/IbEN3qmE?fromSns=

3- Terminal Blocks

http://s.aliexpress.com/u6fMfm63?fromSns=

4- B200K Linear Potentiometer

http://s.aliexpress.com/UNfEzEJb?fromSns=

5- B500K Linear Potentiometer

http://s.aliexpress.com/aqieErQf?fromSns=

6- LTC3780 10A Automatic Step Up Down Regulator

http://s.aliexpress.com/R77vEb6j?fromSns=

7- 16mm Metal Annular Push Button Switch Ring LED 12V

http://s.aliexpress.com/RbYjUFZj?fromSns=

8- Old desktop power supply! I picked mine up online second hand for just a few bucks! there are tons of old computers people are happy to just get rid of so this works great for us!

Step 2: Printing!!

This print is super easy and could easily be made using alternate methods if you dont have a 3d printer! the dimension of the box is 300x100x100mm.

All the files are found here:

https://www.thingiverse.com/thing:3034925

if you do download my files please chuck me a like and follow I love to see people enjoying something I could help make for them! I really do appreciate the support to make these kinds of things!

Print with whatever setting suits your printer best I had 20% infill.

Please note the rear of the encloser may not fit your power supply so please edit to fit!

Feel free to contact me regarding the design!

Step 3: Assembly!

As I've been saying I've kept this design very simple but I think the final product looks fantastic and much better than the ones available online.

I found it easiest to screw my power supply to the back mount then glue both the back and bottom pieces together and add hot glue under the PSU to prop it up straight. Next attach the front and sides.

Optionally you could make all the wiring for the front panel first before attaching it however it makes it very awkward to glue, but really this comes down to personal choice. I've tried it both ways and had no issues either way!

Step 4: Wiring!

Now for the fun part... Kinda

I've tried to make the above schematic as simple as I could, basically +12V goes to the LTC3780 and depending on the fixed outputs you want, attach the correct colour wire to the bannana plug! (The gnd you use for each does not matter, one black wire to each negative plug)

if your 24 pin header doesn't have enough of the values you need feel free to use either the molex or CPU wires!

My switch is a 12V LED switch but LED this is optional. For the LED power I used 12V from the CPU Header. Then connect the green wire to "C" on the switch and gnd to "NO

Step 5: Final Touches!

It's the little things you do that always make your final product seem more professional.

1- I added hot glue to most of my soldering joints to ensure even when moved around I wont have wires touching or put under stress!

2- Potentiometer knobs are a nice touch

3- Secure all lose wires to make it feel more solid. I didn't remove any of the PSU's wires in case I ever felt the need to change or expand on this design. This meant you could hear them move around. This made it feel cheap and is also a bit of a hazard so I bundled them and glued them out of the way. I also secured any other lose wires in the circuit!

4- Labels, obviously you don't want to be confused down the track or others for that matter so I just incorporated some simple labeling to remove any and all confusion!

Step 6: Wrap Up!

I love this final product and that why I wanted to share it with all you makers out there like me! I'd seen many variations for varible supplies but this is by far the easiest and is so much cheaper than the ones you can buy!

I've been using mine for a while now and it's been absolutely flawless!

However there are a few things I might add in the near future to make it even better!

1- Rubber feet, because the plastic tends to slide along the desk unless you hold the back

2- A support in the middle of the case, honestly it holds up fine as is but might feel more premium with a middle support!

That's it you've made a Varible Power supply on the cheap! Thankyou so much for reading my instructable I hope you enjoyed!! Please feel free leave me any tips so I can further improve my skills as I'm only a novice!

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    40 Discussions

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    Cam647davidh1067

    Answer 4 months ago

    The 24V is coming from the LTC3870 module (step up step down converter). This allows the voltage to be adjusted up or down from the 12V input

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    MrJooshCam647

    Reply 4 months ago

    Could also use the +12v and -12v (if provided on your power supply)

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    JimD80

    4 months ago on Step 6

    I maybe wrong but it looks like you left one ground connection off your schematic the ground of the PC PSU to the ground of the case. this completes the ground return for all the PSU voltages.

    8 replies
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    Cam647JimD80

    Reply 4 months ago

    Hey Jim can you elaborate? Dont' quite understand :) Each set of voltages have there own gnd wire.

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    JimD80Cam647

    Reply 4 months ago

    Your right each output has a wire going back to The PSU and a wire to chassis ground. The problem I see is there is no psu wire to chassis ground to complete the PSU ground to chassis ground.

    psu gnd.png
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    pierrard JimD80

    Reply 4 months ago

    Hello JimD80,

    On the schematics you copied from the author, the black indicates it's to be tied to a ground. The plus being the positive.
    As you observed, plastic is not a conductive material, and this means "ground" is all wired together. Now if you observe "Step 5" second picture, you can clearly see the author posted a photo where we see black wires connected to those "ground".

    No offense but did you really get stuck on this? If so, you might want to do a bit of self learning in electricity classes before attempting an assembly like this. Computers' power supplies have high voltage capacitors, bad grounding can bring risk of shocks, and fire..

    Cheers,

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    JimD80pierrard

    Reply 4 months ago

    your are right but I am not refering to the case which is plastic I am refering to the common grounds that should be wired together the one not shown is the ground return to the PSU (see my drawing ) I have been an electronics engineer in areospace , and military electronics for over fifty years so I not "stuck" on this.

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    pierrard JimD80

    Reply 4 months ago

    So are you complaining that the DC power supply doesn't show the ground as wired? On the schematics you shared, Power Supply is represented in the top right corner. It's pretty obvious that the power supply requires also the ground to be wired even the author forgot to paint a black connection there. It would be on the "1" or on the "2", the "3" being a plus (connected) as well as the "4" of the DC.
    Glad you served 50 years, but the way you phrased your request is confusing as you kept referring to "chassis ground". There is no chassis ground, they are wires all connected to the negative/ground.

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    charles543JimD80

    Reply 4 months ago

    Unless I missed something, this is a plastic case. Why would you want to ground a plastic case

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    JimD80charles543

    Reply 4 months ago

    not to the case but the common ground I used and old term "Chassis Ground" when I should have said "Common Ground" anyway The PSU does not show a ground connection common to the outputs

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    charles543JimD80

    Reply 4 months ago

    There is one ground in a PSU. There are multiple black wires, but they all connect to the same place on the printed circuit board. All the red wires connect to the same place. Same for yellow and orange I know this because I have torn PSUs down to the printed circuit board. That is why as it says in the instructable you can use any black wire.

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    RobertTheMaster

    4 months ago

    Iv made one similar to this but yours is far better designed and definitely looks a lot better than mine, I will scrap mine and try and replicate your work I reckon. Thanks for sharing this masterpiece

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    JohnC430

    4 months ago

    How much power is the p/s rated for? and by the way, thanks for sharing. Thats a nicely designed p/s. also, i did not know there is a LTC3870 board out there for sale.

    1 reply
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    Cam647JohnC430

    Reply 4 months ago

    The supply I used is 450W, but really anything 300W or above would be suitable. The LTC3870 goes upto 30V and 10amps, plenty of headroom for most electronics projects.

    Thanks for checking out my instructable, hope it proves helpful for you.

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    charles543

    4 months ago

    What size wire did you use to wire your power supply?

    1 reply
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    Cam647charles543

    Reply 4 months ago

    Hey mate, I've used 16 Ga Wire and this is plenty of head room for my uses (Generally lots of electronics projects wont pull anywhere near this)

    However if you think you will need to pull over around 10amps for any reason i would suggest as said above maybe going up to 12 Ga or doubling up wire.

    Personally never pulled anything near this

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    ee_eng

    4 months ago

    Overall, a nice project! I did want to say that the wiring going to the front panel banana plug ports looks pretty small in the photos. I would recommend that anyone making this power supply use large gauge, heavy duty wire for these connections, 16 Ga at the smallest and perhaps a large as 12 Ga (if you have it). By the way, wire gauge numbers (Ga) are also referenced as AWG numbers. AWG stands for for Armerican Wire Gauge).

    Smaller Gauge numbers numbers have larger current capacity.

    Larger Gauge numbers have lower current capacity.

    If you only have smaller gauge wire, you can also double-up or tripple-up smaller Ga wire (careful to use the same length!) in parallel runs to increase their current carrying capacity.

    Why use large gauge wire? Using larger gauge wiring will minimize the the voltage drop in the internal wiring between the power supply and the front panel. This keeps the project a little cooler and makes the supply safer (internal wiring won't over-heat). After all, we wouldn't want the internal wiring to heat up whenever your project is drawing a lot of current (ie: when running motors, heaters, high wattage lamps/LEDs, etc).

    2 replies
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    charles543ee_eng

    Reply 4 months ago

    The regulator is limited to 10A. 20 gauge wire is rated at 11A for chassis wiring.(http://www.powerstream.com/Wire_Size.htm)It is only rated at 1.5A for power transmission. It all depends on what you are using it for. I would probably use 18 Gauge.There would be nothing wrong with 16 Gauge. Looking at the pictures it looks to me like the wiring is adequate.

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    ee_engcharles543

    Reply 4 months ago

    18 to 20 AWG may work okay, but again, it depends on the current draw of the device under test, the wire length, the total voltage drop one is willing to tolerate, and the wiring temperature rise one will accept.

    I am not sure how you determined the "the regulator is limited to 10A" spec. Perhaps you are referring to the added, adjustable regulator board output limit. However, I would point out that other outputs of the PC power supply will usually deliver much more current.

    The attached photo shows a typical rating plate from a ~400 Watt PC power supply. Here, you will see that the 5V output says it will deliver 35 Amps. If your external circuits routinely draws that kind of power, heavy wiring inside the case is warranted.

    Even if you never intend to use that much power, but it is available from the PC supply, an unintended shorted-circuit wire across the 5V output will easily over stress small wiring. The weak spot in the wiring (either a small wire gauge or a weak crimp/solder joint/poor termination/etc. can act like a fuse by heating up, and/or burning up. Hopefully the power supply has some "fold-back" circuitry for short circuit protection, but if not, on the order of 150W of power will have to go somewhere.

    I've seen things go bad in high current/power connection conditions. Specifically, I've have had an under-tightened terminal screw on my 3D printer heat bed actually result in an overheated condition that begin to unsolder a terminal block from the PC board it was mounted on. All of this happened with a nominal current load of only about 15 AMPS! With that problem fixed and every thing working, I can still feel a noticeable temperature rise (about +5 Deg F) within in the roughly 3 ft of 12 GA wire between the bed controller power MOSFET switch and the bed itself.

    While I agree with your assessment based on a max Current of 10A and the wire size chart you cited (Great link by the way!), I continue to recommend that larger gauge/oversized wiring is inexpensive and worth it, if only as an insurance policy for a dead short condition.

    Take care.

    Typical PS Rating Plate.jpg