The panel meters for my DIY bench top power supply have arrived from china. One is a 20v voltmeter and the other is a 5A ammeter. I ordered them from ebay and at a cost of around £6 each, they are far cheaper than anything available locally.
On unpacking the meters i found this rather interesting note:
It seems that the meters require fully isolated power supplies. It may be possible to power them from battery but then i have to mess about with relays switching them on and off and changing the batteries. Instead i hunted around and ordered some of these DC-DC modules. They are XP-Power IA1209S modules but any dc-dc module with between 9v and 12v isolated output will do. I chose these because they have a 12v input, 9v output and are cheap. They have dual outputs but this just means that they provide a -9v output as well as the 9v output. Obviously the -9v output isn’t needed.
Panel Meter Power Circuit
- 2 XP-Power IA1209S dc-dc modules
- Small piece of strip board (also called vero board)
- 6 lengths of multi-core wire (7/0.2mm core)
Only basic tools are required for this circuit. These should form part of any electronic engineers arsenal, as discussed here. I just used the breadboard as an extra step
When they arrived I tested them on breadboard first:
I’ve drawn up a nice schematic to show how simple the wiring is:
Remember to cut the tracks on the board between the two supply’s outputs if you’re using strip board.
This time I powered up the circuit using the jump starting trick i mentioned in my previous post and tested the output using a multimeter. The output read 10.5v but there was no load on them so this isn’t unusual. After wiring up one of the panel meters, the output voltage dropped to a more sensible 9.3v
Notice that i have a power resistor (large white block) to load the supply and ensure i get a nice consistent dc source. This is sitting between 5v and ground and is 10Ω. This gets quite hot so until i can give it a heatsink and some airflow, i’m only running the supply for short periods.
Next i soldered the dc-dc modules to some strip board in the layout shown in the schematic above. Remember to cut the tracks between all the outputs of the dc-dc modules, you want those outputs to be completely isolated.
The result is some nice blue:
You can see the circuit in the top right, just below the ATX cable connector. I used a salvaged piece of stripboard from my earlier mishap, hence the additional yellow wire to bridge previous cuts. The breadboard is just to help distribute power and to hold the power resistor.
My next step is making the aluminium box that all this will go into. After that it won’t be long until this project is complete