Home > DIY Bench Supply > Power Supply – Case Completion

Power Supply – Case Completion

November 26, 2010 Leave a comment Go to comments


I’ve finished most of the construction and i decided that this project has taken longer than i’d hoped. I wanted to finish it so here is the final build and assembly in one huge post.

Parts Used:

  • My Adjustable Voltage Circuit
  • My Panel Meter Circuit
  • My Aluminium Supply Case (Labelled)
  • 2x DPDT switch
  • Green Binding Post
  • 4x Red Binding Post
  • 4x Black Binding Post
  • 3mm Red LED
  • 6x 3mm Green LED
  • 7x 3mm LED panel clips
  • 4P2T rotary switch
  • Amp Panel Meter
  • Voltage Panel Meter
  • Red Multimeter Lead
  • 2x 6mm knobs
  • ~20cm of 3mm 3:1 Heatshrink
  • 2x TO-220 heasinks
  • ~50 Crimp terminals
  • Lead Free Solder
  • 3x 47 KΩ resistors
  • 3x 5.6 KΩ resistors
  • 3.9 KΩ resistor
  • 820 Ω resistor
  • 12 KΩ resistor
  • 1.8 KΩ resistor

Tools Used:

  • Soldering Iron
  • Crimping tool
  • Snipe nosed pliers
  • Wire cutters
  • Glue Gun
  • Phillips screwdriver
  • 2mm Allen key

For most of this it should be clear how it goes together. The circuit construction just followed my power supply schematic. If there is anything that needs explaining further then feel free to ask. Unfortunately i got a bit carried away at some parts and forgot to take photos, I’m still learning to take my time.

I started by opening the power supply then trimming and twisting the wires into identical pairs, giving me 4 12v pairs, 2 5v pairs, 2 3.3v pairs and 6 ground pairs. These were then crimped so they can be later attached to a terminal block

I then attached a T0-220 heat sink to a 10Ω power resistor using thermal grease and a glue gun. This was then soldered between a spare 5v and ground wire (remember to heat shrink exposed wires) and attached to the side of the supply using twisted wire. Hopefully the hot glue will hold despite the resistor getting quite hot. The picture isn’t very clear but you should get the idea:

This is everything i need to do inside the case so after taking some pics i plugged the internal fan back in and reassembled the case, feeding the crimped wires through the holes in the top of the supply:

As the cables will be attached to a terminal block, i also needed connecting wires for the rest of my equipment. This was made from spare twisted, crimped together of wire from the case. I decided to build all the circuits i would need, outside the case so that the final stage was just an assembly job, this would allow me to diagnose any issues quickly

The indicator LEDs are designed to indicate that each voltage from the supply is working. therefore they each need a supply and resistor value. This is the circuit i came up with:

I used two resistors for each LED because they are all supplied from different voltages and i wanted to match the resistor value as closely as possible. Heat shrink was placed over exposed wires and resistors.

This design allows me to simply solder the resistors to end of the LEDs and solder the other legs together. The resistor is then crimped and attached to the appropriate binding post

Unfortunately i can’t remember what resistor values i used for the red standby LED but they would have been similar to the ones from the 5v LED above.

The indicator for the variable output is actually powered the 12v supply, but switched by the same DPDT switch as the variable output. This is because the variable output goes from 1.2v to 11.8v so using that to power an LED is rather difficult.

The rotary switch in the circuit diagram is going to be used to switch between measuring the variable voltage supply and an external probe voltage. Also, since there is likely to be a small voltage drop across the ammeter it allows the voltage measurement to be switched between ground and the ammeter input. This complicates the design slightly but i feel it is more useful than measuring the fixed output voltages that my previous design allowed.

The panel meters were then fitted and the supply circuit fixed in place. I made simple insulating trays for the circuits i built using an old plastic bottle. The circuits were then mounted in place using hot glue. I then fitted the output switch to the variable voltage supply and wired the indicator LED to the same switch. The indicator LEDs and variable voltage circuit could then be put in place. This left just the binding posts and rotary switch that needed wiring to the appropriate binding posts

Unfortunately i didn’t get many photos of the supply’s internals. It was very cramped in there and i just wanted to get it sealed up, but here are a couple photos from the sides of the case:

On the left side image you can see the terminal block, the power switch and the binding posts and on the right hand image y0u can see the ammeter bind posts, the rotary switch, the sides of the panel meters  the sides of the circuits i built and the terminal block.

Once the case was wired up it was attached to the base supply and voila:

The final result is not quite the same as i planned and I’ve gone wrong a few times, but i have learned a lot. Such as to allow more clearance when bending aluminium and to plan not only where major components are going but also circuit boards and the wires that connect them. I ran out of space in the case very quickly and just had to cram it in and try to seal it with hot glue. Overall i’m happy with the result though and look forward to using this supply for my future projects.

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  1. November 28, 2010 at 11:41 pm

    Every time I think about doing something exactly like this myself, all I want to do crawl under a rock. LOL.

    • December 3, 2010 at 10:48 am

      You should just go for it. I was apprehensive at first but after a while i realised that i needed to put some of my plans into action, otherwise i’ll never learn anything.

  2. Marcus
    December 11, 2010 at 12:22 am

    If you don’t want to waste the power in the 10 ohm resistor then remove it. A working ATX PSU doesn’t need a minimum load to be stable.

    • December 11, 2010 at 11:41 am

      I believe with switched mode supplies you often do. It may be the case that with some supplies it isn’t quite needed but i didn’t want to take the risk. Take a look here for a more detailed explanation than i can give

  3. December 20, 2010 at 8:52 am

    Very impressive project, and excellent documentation as well. Cheers!

  4. January 3, 2011 at 11:11 pm

    Very nice presented/documented project and it looks awesome. Keep it up!

  5. February 1, 2011 at 11:42 am

    Excellent project I am just pricing up the components so I can build this myself. However I’m a bit confused with the 4P2T rotary switch. Is it just a 4 pin rotary switch?

    Kind Regards

    Joe

    • February 1, 2011 at 2:39 pm

      yeh, its just a 4 way rotary switch with at least two throws. This means it has 4 different positions and switches at least two separate connections

  6. Michael
    February 5, 2011 at 1:18 pm

    Hi,
    did the same cause my old power supply burned down and the chips were too old (LM723)…

    For uC circuits this is absolutely an inexpensive solution – great!

    Sorry, but:
    I think you took wrong resistor values for the leds. I took 2mA low-power items, driving them with 3mA at 1.9V. in the 5V lane i took 1k resistors, in 12V 3.3k and in 3.3V part there are 470 Ohms… If you take standard 20mA types, resistors would be about six times smaller than mines. Yours are definately toooo big…

    Because of bad availability of MIC29152WT in germany i took the LM338 which i had a lot (from an old gainclone project). They can drive up to 5A and also have a 1.2V Voltage drop. And with the LM113 reference you can drive downto 0V…

    Really cool idea man! Thanks a lot! You saved my weekend, really!

    Michael

    • February 7, 2011 at 10:47 am

      Hi,
      Glad you found it useful

      My resistor choice was because the LEDs i had were clear lens LEDs and not signal LEDs. When driving them at the rated current they were far far too bright so i put them on a bench supply at work and reduced the current until they were the right brightness. I then based my resistor choice on this current and the voltage across them. Sorry if i didn’t mention that before.

      -tgtomm

  7. Michael
    February 14, 2011 at 2:32 pm

    Hi,
    thank you for your explanation to the leds – didn’t knew that they run with such a small current…
    After i finished my supply i decided to cut off the peripheral supply-cables (that ones for CD/HDD) as close as possible to the board (disassambled the psu) – from that point on the switching psu doesn’t run anymore – any suggenstions? Hate these psus ’cause you cannot point with measurement equipment into without the danger of killing the psu itself completely, the mesurements or yourself – grrrrrr 😦

    Michael

  8. Mike G
    June 10, 2013 at 11:42 pm

    Hi, I’m in the process of doing a similar project to yours and was going to also use a voltage and amperage display, however I found this unit that has both in one gauge and wanted to make sure this would work without any issues, I like that it would take up much less space than 2 gauges.
    http://item.mobileweb.ebay.com/viewitem?itemId=370819097154&cmd=VIDESC

    • June 11, 2013 at 12:43 pm

      The meter looks ok but I would be careful of:
      1. The resolution of the volt meter. It states that it has a resolution of 0.1v. First of all this isn’t great, but also since it has a full scale resolution of 100v, it might not be very accurate at low voltages.
      2. The shunt seems to be a big question mark on this meter. It states there is one built in with a maximum measurement of 10A, but it doesn’t state what resistance this is. That means you don’t know how it will impact your supply voltage. If its a 2 ohm shunt for example, you will have a voltage drop of 2 volts across it when you’re only drawing 1A. You would need to check this when you get your hands on it. I would also recommend double checking its accuracy.

      Tom

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