[SCCC] portable contesting power

[Peter Putnam]

Drew,

I've found several common Icom radios (IC-706, IC-7000) that are not 
happy with your anticipated supply voltage range of 12.0 to 12.8 volts. 
Complaints range from distorted audio to doing a complete power-on reset 
on the first voice peak. Voltage drop in the wiring from the battery to 
the radio plays a role in this issue, so your mileage may vary...

You might find the range of 13.0 to 13.8 to be more suitable. A series 
set of 6 LTO (Lithium-titanate) cells initially charged to 14.0 volts is 
worth considering.

An MPPT solar controller for a "12-volt" system barely outperforms a PWM 
controller when the open-circuit panel voltage is in the range of 21 to 
22 volts, typical for a 100 watt panel. The MPPT controller becomes the 
obvious choice when the panel voltage is two or three times higher than 
the battery voltage.

Don't be tempted to use one of the $15.00 PWM controllers from China. 
They connect the positive panel output to the positive terminal of the 
battery and do the switching on the negative terminals, making a common 
ground connection impossible.

Paralleling solar panels gives disappointing results. If one panels 
voltage is a few millivolts higher than the other, it will deliver most 
of the output while the other panel loafs along. My experiments with two 
identical 150 watt panels in parallel maxed out at only 200 watts. You 
get what you expect if you put the panels in series, but that requires a 
controller that can handle the higher input voltage. The Morningstar 
SS-MPPT-15L, for example, can accept panel voltages up to 60 volts, 
efficiently accommodating two 100 watt panels in series.

73,
Peter
NI6E



On 1/2/2021 12:54 PM, Drew Arnett wrote:
> 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
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