Power Supply – Case Completion
- 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
- 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.