Hi All,
Recently I'd asked for some info with
power supplies on the forum and thank everyone that responded. I didn't quite get to the bottom of what I was after but during the process of investigating gleaned some information that helped me in the end. Eventually I chose to go down the linear
power supply route (despite formerly being happy with a switch mode type) especially after getting the following information direct from a manufacturers site :-
Switch mode power supplies (SMPS) employ high frequency switching and thus, are a source of radio interference, a recipient of radio interference and a conduit of radio interference. (Older linear type transformer based power supplies do not employ high frequency switching voltages and will be quieter as compared to switching type of supplies.)The document then went on to explain some of the issues that arise, suggestions to improve the situation and then the usual disclaimer of how their products comply with the limits laid down in the European Standards for emission and immunity.
This all goes to explain why my noise floor rose by some one to two s-points on the lower amateur frequencies when I switched from a battery
power source to my original switch mode! (No, not 'birdies' but general wideband hash!)
In the end I was gifted (by my lovely wife) a linear
power supply in the shape of the Sharman PS-LM40. (It comes in many manufacturer 'flavours' but also reminds me of the Alinco DM340.) It's a big heavy beast being a linear type and I'd quite forgotten how my last big linear
power supply was such a 'foot warmer' with this unit being no exception. The first time the 120mm 24v fan came on I was taken by surprise and hadn't expected it to be quite so noisy! (It's quiet in comparison to some fan units and if placed sensibly wouldn't be an annoyance.)
I could have gone down the route that many computer style 'modders' do with fancy/specialist fan manufacturer replacement units but instead dug through my drawers to see what I had available and came up trumps with a stock of 60mm Evercool fans.
Time to open the
power supply (and completely void my warranty!
)
There isn't much room inside but a space above the regulator board and behind the (lovely) analogue meters looked promising. The heatsink had some 'spare' tapped holes being a mirror of the other side where the temperature sensor is mounted so looked a good candidate for mounting the fan hardware.
After digging through my workshops/sheds I came up trumps with a sheet of aluminium plate so set about with the fiddly (but weirdly enjoyable) task of cutting, drilling and shaping the mountings I required.
I don't think it turned out too bad....
These are 12v fans so I simply wired them up in series to the cigarette lighter/accessory connector allowing them to run continuously but at a slower speed. They were set to blow in to the PSU being able to drawer air from the left vent slots and wouldn't fight against the original 120mm fan at the rear which is set to blow out of the
power supply when it triggers from the thermal switch.
It is all fantastically quiet now and despite running several radios from this PSU as well as firing up some 25W FT8 action the main (noisy) fan didn't come on once. (I did however plonk a big load of 100W
power resistors onto the
supply drawing some 25A for about half an hour to ensure the main fan came on with the extra heat produced.)
Here's another shot of the additional fans in place...
Overall I'm very happy with this modification but some might ask why you would buy a new
power supply only to have to fit extra fans to it. I didn't have to, but I had the parts, was willing to undertake the work and very pleased with the reduction in noise not only RFI wise but also audibly so.
It would have been lovely to have obtained an Astron or Microset PSU with their huge fan-less heatsinks but I didn't want to take advantage of my fantastic wife's generosity whom I thank immensely for her support of my radio interests.
Boring stuff for some I suppose, but for me the radio interest is much more all encompassing including such frivolities.
Enjoy your radio pursuits no matter what.
All the best,
Victor