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Linear power supply for KiwiSDR & others, fan cooling

I use an old Lamba linear 5V power supply for my KiwiSDR and netSDR (eBay special for $30 w/shipping). It runs warm, still well within specs but I decided to add a cooling fan with a second KiwiSDR on the way. Of course I didn't happen to have at 5V fans laying around, so I went with a 12V fan and an old linear wall wart to power it (the fan only draws about 120 mA). The fan exhausts upwards and pulls air through the power supply. Conveniently the hole spacing for the fan matched that of the ventilation holes in the PSU chassis, so it sits nicely in place with some standoffs.

Without the cooling fan, the power supply chassis runs at about 95F powering just the KiwiSDR, and 101F when the netSDR is also powered up.

With the cooling fan running, that drops to 81F powering just the KiwiSDR and 85F with the netSDR also running. Ambient temperature of the shack at the time was 75F.


  • That'll work a *lot* better if you seal the space between the fan and the perforated case with e.g. masking tape. Stops a lot of air coming in from the side to be drawn through the fan, and forces ducting of interior air to the fan and out.

    It's also likely that performance will improve if you close off the ventilation holes for ~5cm around the perimeter of the fan. That will stop colder exterior air being drawn down through the holes and inside across to the fan, preventing more interior air from moving, as it would be better to force more air to move from farther away within the case and closing off the nearby exterior holes should achieve this.
  • Thanks for the suggestions!

    Here is Version 2.0, I mounted the fan on a piece of plastic (from a kids lunchbox that was going into the recycling bin) to direct more airflow through the power supply chassis.

    The cutout is not terribly neat but works. I drilled a large hole and then use my 35 year old Radio Shack nibbling tool to make the cutout.

  • It'll be interesting to see by how much better the numbers look.. I'm hoping I'm right anyway! :)
    I spent too many years working inside overclocked PCs trying to improve airflow not to try to help if I see something obvious at least.
  • Well, this is curious. The temperature is the same. Within one or two tenth of a degree F anyway. I can cool it about 5F further by blowing air into the chassis vs drawing it out (which seems reasonable). I am not sure if that increases the chance of dust building up inside?
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