Re: Neat power supply!

Arv Evans
 

Most AT and ATX style computer power supplies are shielded by the metal case.  They do lack
shielding in the form of bypass capacitors on the DC leads leaving the case.  This can be fixed
by installing 0.1 mfd capacitors on the DC leads as close as possible to where these leads pass
through the metal chassis. 

Laptop type computer power supplies are a little different because they are designed to charge
batteries and not for directly running devices that have rapidly varying loads.  It is usually possible
to remove some of the RF interference from these units by adding 0.1 mfd on each DC lead, but
the plastic case is the real problem.  Some luck has been had by removing the plastic case and
installing the PCB inside a metal case, with appropriate input and exit RF bypass arrangements. 

Switching power supplies that are designed for constant load can sometimes be made to work
with varying loads by adding 2200 or 4700 mfd capacitors across the DC outputs.  These
capacitors can usually be found and salvaged from dead or unneeded AT or ATX style PC power
supplies.  This might be a good tactic for laptop type power supplies that don't quite have enough
current on peaks to handle the varying load of an SSB or CW transceiver. 

Arv  K7HKL
_._


On Sat, Jun 30, 2018 at 10:56 AM iz oos <and2oosiz2@...> wrote:

I heard that some switching power supply when they fail they may make extensive damage because of leaks of AC, at least this what I was told. In some appliances that had noisy switching power supplies, I wrapped them into aluminum foil and added a ferrite to the vdc cable (wound many times). In the worst cases I connected the foil to ground. I solved completely the issue.


Il 30/giu/2018 10:01, "Raj vu2zap" <rajendrakumargg@...> ha scritto:
Ordered it and will try. I needed a variable PS for some other purpose.
For bitx I use one of the many bench power supplies in my collection.

Earlier I modded a laptop charger to make it variable but without display.
for 12 bucks this looked like a steal with display!

Raj

At 30-06-18, you wrote:
>Looks good, but switch mode supplies can cause a lot of RF interference.
>Have you tried it?
>Cheers
>--
>John VK6JAH




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