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Author Topic: Solar SLA charging and maintenance for unattended transmitters  (Read 518 times)

Offline deciduous

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Hey I'm planing on setting up some beacons sometime soon and I would like to pick everyone's brains in regards to solar charging some sealed lead acid batteries,  I'm looking at using a 7.2 AH 12V SLA, I haven't decided on solar wattage yet, I'm thinking I'll need about 12 to 16 watts of solar to charge, what have your experience's been with solar charging? what's the simplest charging circuit without sacrificing too much battery longetivity? I know its a compromise.

Offline redhat

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #1 on: November 07, 2018, 2238 UTC »
For best efficiency, you could use a switching regulator to drop the panel voltage to 13.6V.  This will float charge the battery.  If you have the batteries outside, the charge voltage should be adjusted to compensate for the difference in charge voltage vs temperature.  I believe -50mV per degree C relative to 25C is the compensation, ie temperature goes up, charge voltage goes down.

Small charge controllers can be had cheaply, it may be worth the expense to get one and let it perform charging and protection for you.

+-RH
Somewhere under the stars...
WinRadio Excalibur/305 w/ a chi-town resonant loop, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Offline Teotwaki

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #2 on: February 15, 2019, 2151 UTC »
I have some recent experience with solar powered boxes and I would advise that you try to do the following.

Record actual current consumption of your electronics and record it in Amp Hours (AH)
Examine the weather patterns for the installation area and look at the number of cloudy days you could expect.
Look at the max and min number of hours the sun will shine during the day from winter through summer.
Build the electronics for minimum current draw when not transmitting; disable unneeded LEDs, etc.
Choose your battery and solar panel sizes based on the data you collect.
Make sure your electronics will restart properly if the battery voltage gets very low or goes near zero.

Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline Teotwaki

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Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline Teotwaki

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Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline Teotwaki

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #5 on: February 15, 2019, 2339 UTC »
Hoping I get this about right.....

Sample data and possible design considerations, single letter beacon transmitting 2 watts RF for one second once per minute

0.074 AH - estimated current consumption
2  - number of cloudy days
5 hrs - minimum the sun will shine during the day in winter
7 hrs - minimum the sun will shine during the day in summer
0.060 Amp minimum current draw when not transmitting
0.300 Amp maximum current draw when transmitting
1 sec transmit time 60 times per hour hour (60 seconds total transmit/hour)

24 hour consumption:

0.06 x 0.9833 x 24 hrs = 1.652 AH        (98.33 is the percent of time drawing 0.06 Amps)
0.30 x 0.00167 x 24 hrs =  0.120 AH     (1.67 is the percent of time drawing 0.03 Amps)

So 1.772 AH total consumption in 24 hours to be replaced by the solar panel the next day plus supporting normal current draw

On the short days of winter we'd have 5 hours of good light on the panel so 1.772 AH / 5 = 0.360 Amps from a perfect solar panel at minimum

Then 0.36A times 18v equals  6.4 Watts so a 10 Watt panel could work. They typically have a 0.55 Amp short circuit current capability

If we had two cloudy days the transmitter would draw 3.45 AH total so a 7 AH battery might be the minimum size to avoid running the battery flat. Snow on a panel or longer periods of cloud reduce charging capacity.

Typical good quality Chinese 10 watt rigid frame panel on Amazon

https://www.amazon.com/ALEKO-PP10W12V-Polycrystalline-Opener-Driveway/dp/B01N5R81WR/ref=sr_1_68?keywords=10+watt+panel&qid=1550273735&s=gateway&sr=8-68
« Last Edit: February 16, 2019, 1700 UTC by Teotwaki »
Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline Pigmeat

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #6 on: February 19, 2019, 1936 UTC »
Some days I come across things on this board that say,"Come back, Pigmeat, come back." lol!

A few solar panels, three of Stretchy's tx's, some appropriate amperage gel cells, and a way to get programming to the tx site and you've got a one man regional shortwave pirate network. You could do the programming with cheap thumbdrives and pawnshop laptops or pads. Who give's a crap if it get's stolen?

You guys are a bad influence on me.

Offline Josh

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #7 on: February 19, 2019, 1959 UTC »
Also don't overlook the environment, moisture and critters will all be trying their best to get in and gum up the works. Also also the sun might try to make things difficult by heating things up that shouldn't be heated.
Conveniently located near Vincennes Indiana.

Offline JimIO

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #8 on: February 19, 2019, 2256 UTC »
"Who give's a crap if it get's stolen?"

That's what I've been thinking about. Micro SD cards are probably the cheapest way to go.
Make it national too. (like an emergency) And play hippie music.    8

In AM mode.
« Last Edit: February 19, 2019, 2301 UTC by JimIO »

Offline Stretchyman

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #9 on: February 20, 2019, 0715 UTC »
I was making a (MW/AM) Tx with built in MP3 player and have had a few 'Requests' for same on SW.

The MP3 players are rather cheap @ <$5, you just have to mill out a rather weird shaped hole in the front of you Tx box, wire it up to audio in and 12V.

Sold a load to the 'TX around your house' crowd.

Anyway Piggy, I have some new designs one being a 10Watter that's only 5x3x1.5, should fit in the shirt pocket of those 'Lumberjack' shirts you all wear over there!

 ;)

Str.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


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Offline Pigmeat

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #10 on: February 20, 2019, 1240 UTC »
LOL! I've got few from Abercrombie and Fitch when they were the premier outdoor outfitter in the world. They belonged to my Grandad. 50 plus years old and some of the indigo ones still bleed dye when you wash them.

It scares me when I wear one and pass a mirror, only to have to do a double take to make sure I'm not him? Same frame, same male pattern baldness. Where's my chainsaw?

You know Jim, we could have Al play the alpenhorn and yodeling to his love goats as an interval signal.

Offline JimIO

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #11 on: February 20, 2019, 1950 UTC »
My I.S. is going to be a loop of the guitar riffs at the beginning of this tune:

   https://youtu.be/BzMPFTXIqWE

One Forever Stamp will send a Micro SD card to anywhere in the country in about 3 days.
That would make a weekly show pretty easy distribute nationally.
 

Offline Teotwaki

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #12 on: February 20, 2019, 2346 UTC »
These are great MP3 players on Ebay for $1.50 and are also very reliable. They run on 3.7 to 5.5 volts and you can run a music queue tone on one track and your mono audio on the other. Will accept USB memory sticks or small SD cards.

https://www.ebay.com/itm/TF-card-U-disk-mp3-format-decoder-board-module-amplifier-decoding-audio-players/312429831354?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20140725133649%26meid%3Db961f1a152684654a42ebba2534c4518%26pid%3D100276%26rk%3D1%26rkt%3D4%26sd%3D362472828095%26itm%3D312429831354&_trksid=p2060778.c100276.m3476

Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline Teotwaki

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #13 on: February 20, 2019, 2349 UTC »
Also don't overlook the environment, moisture and critters will all be trying their best to get in and gum up the works. Also also the sun might try to make things difficult by heating things up that shouldn't be heated.

Wild wood rats are a real PITA. Had to use 1/4" tubular braided shield on solar panel cables
Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline JimIO

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Re: Solar SLA charging and maintenance for unattended transmitters
« Reply #14 on: February 21, 2019, 0515 UTC »
Teotwaki, that's the exact MP3 module I was referring to here:

   https://www.hfunderground.com/board/index.php/topic,48577.0.html

I ordered the diodes and they arrived a couple days later but I never did anything else.
Str. posted a schematic that looks adaptable. Next step would be to figure out the transformer. Probably a small toroid core?

The audio amp is rated 2 watts so you could use it to modulate a 4 watt transmitter.



« Last Edit: February 21, 2019, 0525 UTC by JimIO »