[hpsdr] To Fan or Not to Fan

[John Ackermann N8UR]

I don't know that anyone has done any thermal modeling of Pandora plus 
LPU, but our gut feeling is that you will want to move some air across 
the LPU heatsinks and dropping resistor, particularly if you are feeding 
with 13.8 volts (as opposed to something lower).

LPU needs to dissipate a fair bit of power to drop 13.8 down to 5V at 
1.35A (the draw of an Ozy/Penny/Mercury stack), and while everything is 
running within ratings, the box will get pretty warm.  Mounting a fan 
using the cutouts provided in the Pandora cover will keep things nice 
and cool.

Also, note that there is a new errata for LPU; it's included in the 
errata sheet for the docs.  The PTC fuse in the 5V supply is underrated 
and will go into thermal cutout if you are running a full stack of 
boards.  The fix is to bypass that fuse, as it doesn't really provide 
much protection on top of the regulator's own overcurrent and overtemp 
circuitry.  There's also an optional suggestion about increasing the 
value of the 2.2 ohm resistor to get rid of more voltage in the resistor 
and less in the regulator.

John
----
Tim O'Rourke wrote:
> ***** 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.
> Any thoughts on this and possibly a fan recomendation so I can get one on order???
> Speaking of PA's, it would be nice to have a few independant, read isolated, Keying or PTTOUT outputs for add on "stuff". Some of my "stuff", linears etc, do not like sharing a common keying ground. I added a small relay to Gerd's very nice RX/TX switch which is working FB for my setup now but when Alex and other modules are added it would be nice to have this feature built in. Maybe a card with a few relays and and headers is all that is needed. You could use jumpers to configure.
> Tim W4YN 
> 
> Tim O'Rourke 
> W4YN at ARRL.Net
> Low Power Amateur Radio Rocks 
> Member of Flying Pigs,ARCI,GQRP,RSGB,ARRL Life Member
> NHRA Life Member
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