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[aprssig] Portable Ops from 12v via 115 VAC

Robert Bruninga bruninga at usna.edu
Wed Dec 29 14:18:27 UTC 2004


For long distance portable operation from the car's 12v
system, dont overlook using lots of small wire and an
110 inverter.

Run an efficient inverter at the car to 110 then run
your portable station on  AC using modern switching
supplies.

Even if your 12v rig draws 20 amps peak, this should 
only be about 2 amps over the AC cord and even if the 
drop over 300 feet of zip cord goes down to 90 volts, almost
all switching power supplies these days can still work
and deliver their rated output at the load.

I carry a 300' coil of black #18 zip cord extension cord that is 
smaller than a football.  It can deliver 5 amps and still be 
within ratings (plus it fits through windows and under doors
very well.  Put 5 amp fuses in it so that some idiot doesnt
try to run a heater on it.  And so if it gets abraided or something
it fails safe.

Also, most laptop power supplies these days can deliver around
3 amps at 15 volts and are ideal (small) power supplies for such
operation.  With 3 Amps, you can power most rigs at the 10W
level...  (and that is only about 300 mA over the long zip cord).

Bottom line.  If you need to get 12v from the car more than about
20 feet, unless you carry BIG cables, forget it.  Run the long
distance
at higher voltage so the resistance losses are less.

Bob


>>> wa7nwp at jnos.org 12/29/04 2:37:58 AM >>>


> Bill, are you suggesting this actually WORKS?
> I have a 300 watt inverter (500 surge), and it
> Draws OVER 30 AMPS.  No car alternator will put
> Out enough current to keep up with the drain at idle.
> Are you willing to put a brick on your gas pedal and
> Idle at 3,000 RPM to get enough current?
> 
> I KNOW, I tried it, and within an hour or two my little
> 300-watt inverter will kill the battery WHILE THE CAR IS
> IDLING!  And 300 watts isn't very much to work with.
> 
> For any real extended operation a generator is absolutely
> Critical.

Depends on how much current you need.  I'm planning to keep
my laptops, 12v B&W TV, camp lanterns and basic wifi
router/modem on line.    A full up computer with monitor
pulls around 100 W.   My minimal setup is much less then that.

Some day I'll have some nice generators, until then I have some
heavy cables with power pole connectors that reach the driveway.

(There - I said it.  Started the last power pole thread of the year.  
Good
thing I didn't mention how I put power poles on a 50' AC extension
cord.  :-)   )

Bill


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