[SCCC] portable contesting power

[Drew Arnett]

I've been burning holiday time researching a few things.  Due to not
fantastic radio home location, portable is the way to go for me for
any serious contest effort.  I haven't purchased a genset, yet.  I had
a hypothesis that battery or battery + solar might be a good move.

I'm only considering LiFePO4 (aka LFP) and not lead-acid.  Lead-acid
are cheap as heck, but wow, those things are just what you need for
boat ballast.  Lifetime is supposed to be a lot better for LFP.
(Thousands of cycles!  How do I recoup the $ value of all the unused
cycles if I only use a dozen times a year contesting?  Email me if you
have good ideas!)  No need for battery V boost converter.  90% depth
of discharge at 12.0 V and 12.8 V roughly for much of the discharge.
I think battery efficiency for a cycle is 90%.

I'm factoring in a lot of things, but still rough numbers.  Need some
margin, but margin is easy to get.  Reduce PA power by 1 dB is 80% for
example.  Assuming camping someplace without shade during day and
sunny skies, etc.  Overall, I think my ballpark figuring isn't far
off.

Baseline:
Renogy 100 amp-hour 64 lbs $212 @ Home Depot
--> $2/amp-hour

LFPs data points:
Renogy 100 amp-hour 26 lbs $765 shipped, can be paralleled
--> $8.5/amp-hour, figuring 90% usable depth of discharge
Renogy 170 amp-hour 48.5 lbs (tempting!) $1275 shipped, can be
paralleled (but why?)
--> $8.3/amp-hour

Does Renogy offer discount for will-call at their SoCal location?  For
hams like that other brand?  For group buy quantity?  I haven't asked,
yet.  I picked Renogy at random, mostly because Home Depot sells them.

These batteries have BMS to keep the battery healthy.  Can be set to
shelf mode for safety, perhaps during transport, assembly,
disassembly.  They offer an inexpensive display panel to show load,
capacity and current charge/load rate.

If willing to try random brands, I see stuff as low as sub $6/amp-hour
shipped.  (If someone has info or has done homework, let me know,
please!)

For solar, I don't have time this year to chase down RFI.  Genasun has
a stellar reputation.  (If someone has info or has done homework, let
me know, please!)  So, another data point:

Genasun GV-10-Li-14.2V $135

That wants to be paired with a 100W panel.  (Their support is good,
talking to them about options.)

Grape 100W panel at Home Depot $72

No RFI to mitigate (I hope!) unlike even the great Honda gensets.

For each panel/controller pair above, can supply load and/or charge at
up to 100W per set.  Parallel those to retop batteries.

Using a couple of web tools, I was able to get the amount of charging
for fixed position (tipped per time of year) or move several times
through the day for SoCal for some of the big events during the year.
Ranges from 5.3 to 8.7 equivalent hours a day.  (Nice to be in SoCal!)

Interestingly, the time of day of start does have an impact on
battery/panel tradeoff.  FD is about the easiest and CQ WW the
toughest out of the events I analyzed.

Assumed 90W load.  RPi/KX3/KXPA100 100W TX 25% duty cycle

100 amp-hour + 0 W panel --> 12.9 hours runtime for $764
170 amp hour + 0 W panel --> 21.9 hours runtime for $1274
200 amp hour + 0 W panel --> 25.7 hours runtime for $1528

A pair of 100 amp-hour batteries paralleled for 24 hour portable
contests looks not bad at all.  Just top off a month before you go.
Use $200 of solar charge capability at home.  Hard mount in your
vehicle?  Takes up little space.  Drag out the panel, too, to run the
fan during the day.

FD (24 hr) 100 amp-hour + 100 W (sleep 2 hours)
SS (24 of 30) 100 amp-hour + 200 W (sleep a bit less than 4 hours the
first night)
CQP (24 of 30) 100 amp-hour + 100 W (designed for solar!, sleep the
same 5 hours as everyone else)
IARU HF (24) 100 amp-hour + 200 W (maybe 2 hours of downtime, not
designed for solar for our time zone)
CQ WPX (48) 100 amp-hour + 200 W (sleep 5 hours a night)
CQ WW (48) two choices:
100 amp-hour + 300 W (39 hours, sleep 5 hours a night)
200 amp-hour + 200 W (don't sleep)

There may be a mistake above.  I'd calculate before a specific event,
anyway, as I'd want planning notes.  Tilt angle, power budget over
time & strategy, etc.  (If anyone knows of a writeup of this sort of
analysis that I could use instead of doing this myself, let me know!)

No RFI.  Possibly very little bulk, at least for 24 hour contests.  A
couple of panels for longer contests.  No RFI.  No gas can.  No gas
engine maintenance.  Bulk of a couple of panels versus generator &
jerry can.  (Those thin monocrystalline panels offered by several
vendors for $200 for 100W would be easier to stow.)  More criteria for
choosing location.  More susceptibility to weather.  :-)

Really no significant price difference, unless scaling up for CQ WW
(in the dark of winter) or for other reasons.

No QRO, but as a CW op, I'd be thinking class E amplifiers.  (How come
no commercial class E CW amps on the market?  So great for portable
power.  And think about the lack of heatsink/fan/weight/bulk.

Hmm.  If I'm writing my own contest logging software, I could have it
display the power situation, too.  Perhaps throttle the rig power 10
or 20% when needed.  Etc.  :-)

Best regards,

Drew
n7da