[aprssig] Emergency Power for Ham stuff

Robert Bruninga bruninga at usna.edu
Tue Jan 19 19:56:37 EST 2016

>>> 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

Oh, and the laptop power supplies I tried had isolation from input to
output.  No common ground.


There are plenty of isolated DC/DC converters on the market that will take
up to 800 volts DC input and convert it down to 12 or 24 volts output safely
(the important thing is the full isolation) that you can then use for other
tasks.  They typically also provide low dropout voltages (30 VDC) and peak
power tracking.  Plus you can combine panels with them such that a panel can
be partially shaded without affecting the others (just like grid-tie
inverter modules but with DC outputs instead).

A much better idea than a AC/DC switching supply.
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