[aprssig] Emergency Power for Ham stuff

[KF4LVZ]

On 2016-01-19 16:56, Robert Bruninga via aprssig wrote:
>>>> Is there particular reason you're looking at powering a full blown
>>>> laptop?
> 
>>> Not a “laptop”, but a “Laptop supply” which can power all kinds of
>>> stuff and are readily available by the box full at most hamests and yard
>>> sales.
> 
>> Or you skip the inefficiency snad safety issues of using an AC/DC
>> switching power supply and use a direct DC/DC converter from the panels to
>> whatever project you want.
> 
> But every AC/DC switcher is just a DC/DC supply with a rectifier in front of
> it.  The only loss of efficiency is the primary drop across the bridge
> rectifier or about 2 volts out of 100 to 330 volts..  An inconcequential
> loss compared to the ubiquity of laptop and all kinds of other universal
> input supplies.  I have even run 25 amp 12 volt Kenwood Ham radio supplies
> on 200 VDC input just fine for powering Field day tents over hundreds of
> feet of zip cord (after removing the internal 115/230 volt jumper) and
> TAPING the ON/OFF switch in the ON  position so no one could try to turn it
> off.
> 
> Oh, and the laptop power supplies I tried had isolation from input to
> output.  No common ground.
> 
> Bob, WB4APR

Bob, you should know better than to use the word "every".  There are
plenty of cheap power supplies out there that will not fit your "every"
description.  I've had plenty of switching supplies that were most
certainly not isolated.  It only takes looking at many schematics out
there to see that it's not always an isolated design.  You have to have
a transformer (and not just the flyback of the switcher which frequently
is not configured as an isolated transformer, you need a full galvanic
isolation transformer) to have an isolated supply.  If you have just a
diode front end going to the oscillator there's no isolation.  Google
the schematics, you'll see them.

You are also describing a "come as you are" approach and many people are
not going to have quality power supplies, they're going to have
rock-bottom-cheap power supplies that could prove dangerous.  Many
laptop supplies are also ultrasonically welded shut so there's no way to
easily and safely open them to inspect the circuit (of course many of
the come-as-you-are people may not know what to even look for if they
opened it).