I changed from a switching PSU to a linear PSU last year, after my switching PSU decided to run the fan all the time, which by all accounts was a common problem. Fortunately Maplins exchanged it and i paid the extra and got the much larger, heavier and better linear PSU.
If anyone knows what the ?? are in one of the photos please let me know, the fan connects to it before running back to the thermostat.
Original I owned a PS30SW II from Maplin, which is a great small PSU, but the fan circuits clearly have a problem. Maplin exchanged it for me and I was able to upgrade by paying the difference and bought a Palstar PS-30, on opening the box it was actually a Manson EP-925 exactly the same PSU but with a different label. Maplin do state it has a thermostatically controlled fan, which to be fair, it does, but its either off or on with no adjustment in fan speed, a rather irritating feature given the complexity of the PSU.
A quick google search showed up a few modifications that end users have done over the years, BUT it would appear that the newer units have some of these features already inside, and the pictures of the inner workings of my PSU differ to those I have seen on the internet.
Now before we get carried away, i am no electrician, but i can use a soldering iron and a multi meter and i’d like to think a fair degree of common sense. Now this is a big heavy PSU, big in both current and weight. So do yourself a massive favour and if you want to mess with the inside switch it off and unplug it, that doesn’t mean that there isn’t stored energy in the PSU so you may want to leave it overnight etc before poking your fingers around some of the large capacitors! Or figure out a way to suck the juice thats left out, after all no one likes a large electric shock especially a DC one. So you mess with these at your own risk.
I opened up the PSU and the fan fitted to mine was a 2 wire Sunon EE80251S1-0000-A99 DC 12v 1.7W, 3200 RPM Fan at 33dB(a) with no speed sensor. It seems to be a cheap 80cm case fan. So getting a super duper one was going to be pretty easy as all those computer overclockers love there speed but only if its quiet :-)
Rummaging around my junk i found an old 80cm fan i had took out of the back of a NAS device. Taking the fan out of the PSU was easy the screws on the back release it, and there was plenty of spare wire inside the case, well that was until i cut it too short :-(
The fan I have used instead of the stock one is a Y.S. Tech Fan Model Number FD1281255S-1A however the voltage range is a little less, but i checked it first and it works fine. The noise is a great deal less even at full speed but both fans produce similar amounts of air flow but the newer one does so at a far less RPM so the noise is lower.
As always if you have any questions please ask, i may place a resistor on the thermostat on the heat sink, but i have got the recommended one to hand. I’ll see how i get on with the fan first.
But it must be easy to add a true thermal sensor to the fan control and units can be bought on ebay that do control the fans based on a predefined temperature.
Remember elastic trickery hurts if you don’t take your time! and switch everything off!
Further mods can be found here