[hpsdr] To Fan or Not to Fan

[Willi Reppel]

Hi all,

I had problems before with Flex Radio´s SDR1000 and its heat dissipation 
plate with mounted 5 V regulator under the stack of boards. Frequent heating 
and cooling (expansion and contraction) of the boards  led to changing 
contact resistance and sudden malfunctions. I had to twist the boards and 
/or entire board stack to get the radio back to operation.
For the HPSDR project I bought a toroid transformer with 2 x 15 V secondary 
output windings and removed by try and error enough turns from the outer 
secondary and lowered the voltage of one of the 15 V ac transfor-mer 
windings so that the 5 V dc regulator sees approx. 7.5 V dc at its input. It 
is reasonable to let a transformer do what it is intended for instead of 
dissipating energy with a fan to ambient and, LOL, contribute to global 
warming.

vy 73 de
SM6OMH  Willi
Atlas, Ozi, Penny, Mercury and IC 735 PA module.


----- Original Message ----- 
From: "John Ackermann N8UR" <jra at febo.com>
To: <g4fre at g4fre.com>
Cc: <hpsdr at lists.openhpsdr.org>
Sent: Wednesday, June 03, 2009 4:50 PM
Subject: Re: [hpsdr] To Fan or Not to Fan


> ***** High Performance Software Defined Radio Discussion List *****
>
> Dave, note the newly updated errata sheet.  The 5V regulator is operating 
> within spec, but as a linear regulator it's dumping a lot of heat moving 
> 1.35 amps from 13.8 down to 5 volts.
>
> My personal recommendation is to replace the 2.2 ohm 10 watt dropping 
> resistor ahead of the regulator with either two 1.8 10 watt in series, or 
> two 6.8 10 watt in parallel.  That doesn't reduce the total heat, but 
> moves more of it into the resistors and out of the regulator.
>
> John
> ----
>
> g4fre at g4fre.com wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> running my lpu off 13.8v to power penny, ozy and mercury, after 4 hours 
>> on receive i can burn my fingers on the lpu heatsink
>> I have reverted to my  pico-psu 90 which hardly gets warm under such 
>> conditions. I dont get noise issues, or none i can notice in my urban 
>> environment
>> Dave
>> ww2r
>> Tim O'Rourke writes:
>>> ***** High Performance Software Defined Radio Discussion List *****
>>> I am awaiting Pandora and wondering about fan requirements in general.
>>> I have mine mounted in a mini-atx case with 5 watt pa and the 
>>> temperature in the case does not seem to be an issue. That was the case 
>>> until I installoed the LPU which disapates significant heat when left on 
>>> for extended periods. Assuming that we will be using LPU for a while it 
>>> seems like a fan for Pandora may be necessary even with out a high 
>>> output PA.
>>
>>
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