[aprssig] Tesla Field Day mode (reducing the 250W overhead)

Robert Bruninga bruninga at usna.edu
Mon Mar 4 10:15:54 EST 2019

Ah!  It can work well!  90% of all FD entries operated at 150W or less

N8HKU, author of the QST article on running an event for 5 hours reports
that his plugin-hybrid's overhead was about 250W (like the Prius too) and
the station only drew about half that.  He could have done that for about 12
hours before the engine would start.

So the solution to lasting all 24 hours is to only run the FD station as
normal from the 12v car battery (with any inverters needed) with the "HV
system" OFF, and then only power-up the car periodically to recharge the 12v
battery.  This would drastically reduce the lost 250W overhead power, and
more than double the duration to the full 24 hours of Field Day but It would
need constant monitoring of the 12v battery to know when to power up the
car's HV DC/DC converter system to recharge it.

But this way, even the small 5.5 kW battery in a plugin-hybrid would last
the full 24 hours of Field Day and meet the rules of not charging by gas.
Oh!  And also this allows for the addition of a 12v solar panel to help
along with no special additional hardware.  My take would be to bring a
separate 12v battery for FieldDay loads so as to not risk running down the
PHEV.  Then parallel it with the car every few hours when it is time to

This x5 all-battery multiplier for all contacts is nice for score


-----Original Message-----
From: Robert Bruninga <bruninga at usna.edu>
Sent: Friday, March 1, 2019 12:54 PM
To: aprssig at lists.tapr.org
Cc: Robert Bruninga <bruninga at usna.edu>
Subject: RE: [aprssig] Tesla Field Day mode (versus the rules)

I just looked at the FD rules, and it looks like using just a hybrid would
sacrifice points, since the battery is recharged by a "generator" and you
could not use points as being a battery station.  It still beats using a
generator though..

A plugin Hybrid has a bigger battery and might operate 20 to 30 times longer
before the engine started, but it still wouild disqualify the battery
multiplier points if the engine recharged the  battery.

A pure EV has 50 to 100 times the battery capacity and would run the entire
24 hours on battery and have no gasoline component at all.

As to power, it looks like operating at more than 150 Watts divides all
scores in half, and so generally  it is unlikely that many stations haul out
kW linears to Field.

And as Rick Green pointed out, all these cars have to be in the ON or READY
condition to provide external power and the parasitic loads need to be
considered.  A Prius draws about 250 watts just sitting there.  And so even
if no power is drawn, its engine will start up every several minutes.
A plugin hybrid with 20 times the battery capacity has been demonstrated to
run a poertable operation for 6 hours and still only used half the battery
capacity without an engine start.

So it looks like this topic is worthy of a closer look to all the details
and nuances against the variety of rules to optimize the solution.

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