| |
M1BYT > TECH 24.09.03 19:15l 72 Lines 3275 Bytes #999 (0) @ WW
BID : 461919M1BYT
Read: OE5AKM DB0FHN GUEST OE7FMI
Subj: Re: Pwer Supply Fan Mod
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<GB7FCR
Sent: 030924/1234Z @:GB7FCR.#16.GBR.EU #:16439 [Blackpool] FBB-7.03a $:461919M1
From: M1BYT@GB7FCR.#16.GBR.EU
To : TECH@WW
G4EBT Opined with considerable skill:-
> Not wishing to labour the point, I would again sound a note of caution
> concerning messing with the cooling arrangements on these PSUs. As
> previously explained, the heatsinking is very poor, and the heatsink
> is shielded from the fan by the transformer, further exacerbating the
> problem.
Hi David,
I can understand the caution, but one of the problems is the lack of
adequate cooling under low current draw. The changes I suggested address
this by keeping the fan turning over at all times, yet the extra
circuitry is in parallel with the existing fan electronics, which should
improve the reliability of this at least.
You suggest the airflow is poor, due to the transformer being in the way
of the flow from the fan and heatsink. Just a thought, perhaps the
solution might be to exchange the transformers location for that of the
heat sink, and turn the fan around. Cool air would be drawn in at the
back, blown straight over the heatsink, then out past the transformer to
the exit grills.
> It does seem ironic that whereas such an over-voltage protection circuit
> would use say a thryristor, four R's, a preset pot, and a cap - 7
> components in total, the Manson EP925 (and similar variants) which offer
> no over-voltage protection, already uses 13 components in the fan control
> circuitry, and some people seem intent on adding another dozen.
Providing the extra components are in parallel with the existing
circuit, and thus increase the reliabity of what is already there, then
I do not have an issue.
I remain puzzled as to why the manufacturers went to such great lengths
in including so many components in the circuit, to just perform a simple
switching operation. All that was needed was a thermal switch which MADE
on rise in temperature in series with the fan, running from a 12v DC
source.
> For my money, and outboard crowbar circuit would be a must, unless I was
> just using the PSU to float charge a battery or run some fairy lights at
> Christmas.
As the power supply is designed to be variable voltage output (3v to
15v), then an over-voltage protection circuit needs to track that
setting if it is to be of more general use.
An external crowbar circuit is well worth while where the PSU is being
used to power our most common 13.8v equipment. G8MNY regularly sends out
ASCII diagrams, one of which I think is a crowbar circuit which from
memory would be perfect for this application.
ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
º 73 from Harry, M1BYT @ GB7FCR.#16.GBR.EU º
ÌÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ͹
º International Museums Weekend 19th+20th June 2004 º
º www.ukradioamateur.org/imw/index.html º
ÌÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ͹
º The ARC's FL/RAE courses + Newcomers Intro to º
º to amateur radio:- http://www.ukradioamateur.org/ º
ÌÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍËÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ͹
º QTH: Garforth, W. Yorks.. º Timed 12:33 º
º harry.m1byt@tiscali.co.uk º 24 Sep 2003 º
ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÊÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ
Message sent using WinPack-Telnet V6.80
Read previous mail | Read next mail
| |
