HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: deciduous on November 06, 2018, 1131 UTC
-
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.
-
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
-
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.
-
I have had excellent results from these Chinese MPPT charge controllers, around $4 on Ebay
https://www.ebay.com/itm/MPPT-Solar-Charge-Controller-Step-down-Charger-for-12V-Lead-Acid-Battery-Packs/333045965670?hash=item4d8b162366:g:qkAAAOSwpzRcUrDj:rk:1:pf:0
(https://i.ebayimg.com/images/g/58wAAOSwaSVcUrDi/s-l1600.jpg)
These DC-DC converters have also been very reliable, only $4 for 10 of them on Ebay
https://www.ebay.com/itm/1x-10x-LM2596S-DC-DC-3A-Buck-Adjustable-Step-down-Power-Supply-Converter-Module/332711109230?ssPageName=STRK%3AMEBIDX%3AIT&var=541841219941&_trksid=p2060353.m1438.l2649
(https://i.ebayimg.com/images/g/5ckAAOSwSzpbPvut/s-l1600.jpg)
-
simple way to log your Amp hours on the actual circuit is with these cheap DC analyzers from Ebay, from $9 and up
https://www.ebay.com/itm/Digital-LCD-RC-High-Precision-Watt-Meter-Power-Volt-Amp-DC-Analyzer-60V-130A/292658364532?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D56426%26meid%3Dc470491471544e72ab477f6caf466ce5%26pid%3D100005%26rk%3D2%26rkt%3D12%26mehot%3Dpp%26sd%3D332842175015%26itm%3D292658364532&_trksid=p2047675.c100005.m1851
(https://i.ebayimg.com/images/g/FXQAAOSwWotbqd~V/s-l1600.jpg)
-
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
-
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.
-
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.
-
"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.
-
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.
-
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.
-
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.
-
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
(https://i.ebayimg.com/images/g/0S8AAOSwQrVb1CQZ/s-l500.jpg)
-
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
-
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.
-
There's quite a few MP3 players but I prefer one with a Bezel so it can be mounted into case and has 5V reg on board;
https://www.ebay.com/itm/5V-7-12V-Mini-MP3-Player-Module-with-USB-IR-Remote-Controller-Player-for-Car/152928501419?ssPageName=STRK%3AMEBIDX%3AIT&var=452693777039&_trksid=p2057872.m2749.l2649
Str.
-
Nice! Only one problem: "Does not ship to United States" :'(
-
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
Some folks have found relief by smearing the cables and whatnot with hot sauce, the critters don't like that too much but it will have to be reapplied occasionally. Can also apply it to furniture legs that attract our four legged friends.
-
Some folks have found relief by smearing the cables and whatnot with hot sauce, the critters don't like that too much but it will have to be reapplied occasionally. Can also apply it to furniture legs that attract our four legged friends.
Hot sauce would be okay for a local site but the braided cover has ended my wood rat problems. No cables damaged in almost two years!
-
Another enhancement for remote battery powered gear is to add in a Low Voltage Disconnect. The SLAs will be damaged if repeatedly run down below 12 volts so I've tried some different circuits and finally settled on one based on the LM339 quad comparator IC.
I ended up choosing 12v as the cutoff point and 13.2v as the reconnect point as that is where the solar panel should be supplying some good current to the battery.
What I found is that the inverting comparator wants to switch very quickly but the battery voltage can get "noisy" with a discharged battery being ramped up quickly by a solar charge controller. There was some "dither" at the 13.2v "ON" trigger point and I I had to add in some capacitors to add in a small delay to the switching and make the on/off cycles cut over cleanly. The comparator's voltage reference is based on a low power 78L05 and the comparator's output goes low for the "ON" condition. That output is applied to pin 5 of the main IC (LM2596S-ADJ) in the switching regulator.
(https://i.ebayimg.com/images/g/5ckAAOSwSzpbPvut/s-l1600.jpg)
-
This has stirred an interesting idea. Use a prepaid lte modem to get an internet connection to the transmitter. Have a raspberry pi or similar to poke an internet stream, and if available start up the transmitter and process the audio. Should the battery get too low, throw noises in the audio and shut down. A max time limit could also be placed on any day based on weather conditions.
+-RH
-
With an internet connection and a raspberry pi or similar you could do anything.
Got line of sight? Then you don't even need internet.
https://help.ubnt.com/hc/en-us/articles/205197750-airMAX-Which-product-should-I-use-
~
-
The idea was to put something out in the hinterlands of nowhere. Like the beacons of the SW, put it up in a state park, wilderness area, etc.
+-RH
-
There's a # rapberry_pi channel on the HFU Rocket.Chat... 8)
~
-
Even better than a pi would be a thin client. They run on 12VDC. Just put ubuntu server on it.
https://www.ebay.com/itm/Wyse-Dell-Dx0D-Thin-Client-D90D7-16GB-Flash-2GB-RAM-909654-01L-No-Stand-Adapter/193112113734?hash=item2cf6610246%3Ag%3AKQ0AAOSwDhFdhBLv&LH_ItemCondition=3000
~
-
I think the power consumption vs performance would still be better with a pi which uses a maximum of 15 watts. Power budget is pretty thin as it is, and no one wants to put up a 200W array to run this thing. Either way, a big battery will be required, probably around 100AH.
+-RH
-
When I wanted to start playing with single board computers I got one of these:
http://www.orangepi.org/orangepizero/
~
-
Hard to imagine that you'd need a Pi . For beacon work, an Arduino seems more than enough . There's more than enough IO pins to sense/control things. You can put the thing to sleep in ultra low power mode (low single digits mA at LEAST without a lot of work.
There's a LOT of capability in the nanos for $2.
My .02
S.
-
This was a hypothetical idea of placing a transmitter off grid and using 4G to get an audio stream, process, and transmit the program material. An arduino certainly does not have the horsepower to do that.
+-RH
-
This was a hypothetical idea of placing a transmitter off grid and using 4G to get an audio stream, process, and transmit the program material. An arduino certainly does not have the horsepower to do that.+-RH
There are quite a few ideas floating through this thread. The OP asked for solar charging for beacons then one tangent was about Arduinos for CW then somehow audio streaming got worked in. If we don't quote who we are responding to it gets a bit confused ;D
OP's message
Hey I'm planing on setting up some beacons sometime soon and I would like to pick everyone's brains in regards to solar charging some sealed lead acid batteries, I'm looking at using a 7.2 AH 12V SLA, I haven't decided on solar wattage yet, I'm thinking I'll need about 12 to 16 watts of solar to charge, what have your experience's been with solar charging? what's the simplest charging circuit without sacrificing too much battery longetivity? I know its a compromise.
-
Redhat, you may find this interesting:
https://github.com/botletics/SIM7500-LTE-Shield
~
-
That shield could be useful for a lot of projects
(https://images.squarespace-cdn.com/content/v1/58618f5fb8a79be3599e04d3/1532441236425-8QDGYN8XZCA57YGIYLDS/ke17ZwdGBToddI8pDm48kDHPSfPanjkWqhH6pl6g5ph7gQa3H78H3Y0txjaiv_0fDoOvxcdMmMKkDsyUqMSsMWxHk725yiiHCCLfrh8O1z4YTzHvnKhyp6Da-NYroOW3ZGjoBKy3azqku80C789l0mwONMR1ELp49Lyc52iWr5dNb1QJw9casjKdtTg1_-y4jz4ptJBmI9gQmbjSQnNGng/SIM7500+Shield+USB+Attached+Module+On.jpg?format=500w)
-
Been playing with the PiZero with WiFi a bit. . Lotsa capability for 9.99$ and a 1.5 watt consumption.
A 30 min transmission followed by deep sleep for a week, with occasional wakeups to check battery voltage should be workable.