Sunday, 23 September 2012

Power Supply in the Box working!

So after some time....I have been busy again!

I have finally placed the power supply in a case and added some volt meters and checked everything works. I have also updated the circuit diagram as I wanted to reflect the extra components that I've added.  Here is the updated diagram:

I added a 3A fuse on the live side of the 230V mains input.  This is to ensure that no matter what happens at the output no more that 3A can be drawn by the power supply at the mains input.  It's purely a safety issue and in my opinion is critical.  I also added a mains rated switch so that it is possible to isolate the power supply from the mains without removing the plug from the wall socket.  Next I earthed the metal parts of the case by connecting the safety earth  from the plug to all of the metal parts of the case and finally I have added some digital voltmeters.  I bought them off ebay from this vendor although there are plenty of them around:

delhanway2009 - ebay listing

Its a standard 3 wire digital voltmeter.  I was hoping to use one as a current meter when combined with a 1 ohm resistor but that hasn't worked.  I need to investigate how these meters works....Anyway they work perfectly for displaying voltage and that is really all we need for this power supply.  When I was building the power supply I took extra care to make sure that all the wires were correctly restrained and none of the low voltage DC wires could every touch the high voltage AC wiring or exposed parts of the circuit - heatshrink and electrical tape all the way!

Here is the completed power supply below:

I'm very happy with how it came out!  It works perfectly and provides plenty of current.  I upgraded the voltage regulator to an LM338 to make sure I can get about 5A if required!  The LM338 is exactly the same voltage regulator as the LM317 but it is able to provide more current.  The datasheet for the LM338 is here:

The power supply gives out at least 30V when loaded at 1A so it works well enough for all my linear power supply needs.  The regulator has built in over temperature and over-current protection so it shouldn't suffer from any of my mistakes and should last me for at least a good twenty years....Happy days!

Here is a quick video showing the power supply in operation.  I should really have connected a light bulb or something to the output to prove it works....I will upload another video later showing it powering a load.

Here is a video of the power supply driving a 12V light bulb:

That's it for now - take care always,