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 Samlex SEC1223 power supply fan mod
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 Return to top of page · Post #: 1 · Written at 5:40:02 AM on 16 September 2020.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 795

The Samlex SEC1223 power supply has an internal fan that should turn on when the supply gets hot. But the thermostat must be set rather high, the supply gets warm bur not hot without it ever activating. So I figured I'd make the fan be dual powered. Normally the fan is controlled by a transistor, Q5, a 2N2222. The fan positive lead goes to the 13.8V output, and the negative lead goes to this transistor's collector. If the thermostat goes open, the transistor turns on, turning the fan on. I added a 68Ω power resistor from ground to this transistor's collector, to run the fan at a low power level, and low audio noise, when the supply isn't so hot that it triggers the thermostat. This will keep the supply cooler, and should help make the caps last longer.

 Return to top of page · Post #: 2 · Written at 6:58:29 AM on 16 September 2020.
Fred Lever's Gravatar
 Location: Toongabbie, NSW
 Member since 19 November 2015
 Member #: 1828
 Postcount: 1039

Hi Wa2ise,
Good idea using the TO package resistor.

I used the same tactic on a Studio Bass amp where the fans were far too noisy for quiet use but used PW5 package resistors across the thermostat
Most of the time the fans just idle away and keep the heat sinks at warm, if the volume gets cranked up then the full fan noise does not matter!

The TO package could bolt onto a heatsink or chassis nicely.
Have not seen them for sale.


 Return to top of page · Post #: 3 · Written at 3:05:18 PM on 16 September 2020.
GTC's avatar
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6367

I have some low noise Arctic brand fans that I bought to replace the noisy fans in my Tenma power supply which operate full blast regardless of load. They come complete with a temperature sensor that varies the fan speed with load demand.

 Return to top of page · Post #: 4 · Written at 4:16:00 PM on 16 September 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 2088

I have a bench power supply that runs its fan at a few different speeds depending on the load.

 Return to top of page · Post #: 5 · Written at 6:54:55 PM on 16 September 2020.
Tinkera123's Gravatar
 Location: Melbourne, VIC
 Member since 5 October 2009
 Member #: 555
 Postcount: 447

Ditto ... I think mine was a thermostat driving a Pulse Width Modulator chip, driving the Base of a transistor.
Wa2ise solution is an elegantly simple alternative.

Cheers, Ian

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