[aprssig] Emergency Power for Ham stuff

jimlux jimlux at earthlink.net
Sat Jan 23 13:36:25 EST 2016

On 1/20/16 10:00 AM, aprssig-request at tapr.org wrote:
> It's good to be cautious, but properly installed, it shouldn't
> be any more dangerous than plugging any appliance into a 230V
> outlet. I don't think Bob intended for anyone to be fiddling
> with live wires from a high voltage solar array in full sunlight
> with bare hands while standing in a puddle.
> Of course, I'll never forget reaching into my first power
> supply and learning the hard way why a bleeder resistor should
> have been installed across the filter capacitor!

Aside from the "DC will support a continuous arc so switches and fuses 
intended for AC don't work" there's also the "solar panels put out 
significant power even when there's no direct sun".  It's really hard to 
"turn off" a solar panel, which raises all sorts of issues for people 
like firefighters.

You can short the panel output, of course.

With respect to the isolation or not. I'd not be too confident of 
isolation.  Your laptop might have secondary DC/DC regulation on board 
to get the 5V, 3.3V, etc. and that might be what they're depending on 
for isolation.  The bulk converter taking line voltage and making 12-20V 
DC may not be isolated, if they think that there's no hazard: connector 
designed so you can't touch an unisolated conductor.

I would think that anything with a coaxial style DC connector is 
probably isolated: the barrel is exposed.

I would think that the Apple Magsafe type connector is also isolated: 
the pins are exposed and easily touched.

But the molded 2-3 pin connectors that have the socket contacts 
recessed? perhaps not.

BTW, using plug/socket as your disconnect (instead of a switch), can be 
pretty exciting if you're drawing significant current. You can draw a 
surprisingly long and hot spark from a 100VDC supply with a lot of 
current behind it.

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