Solar Powered Weather Station

Hello, Thanks for taking the time to read my thread!

I've got a small issue which i'm sure is probably easily solved but i havn't been able to figure it out.

Basically, i'm trying to operate a small weather station that requires two double AA batteries to operate. The weather station is mounted about 30 ft up in the air, and changing the batteries or running a powercord down the pole would be less than optimal.

What i'm trying to do is make something that will deliver 3V AC to the unit, day and NIGHT. I'm assuming you need some sort of battery to provide power overnight, but if you use the solar panel to charge the battery, i've heard you need a higher voltage, so i wouldn't be able to use it to power the station since it requires 3 V...

If you have any ideas please let me know...

Basically, day and night i need 3DCV out

Comments

  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Solar Powered Weather Station

    3 volts A/C?

    Tony
  • solarvicsolarvic Solar Expert Posts: 1,060 ✭✭✭✭
    Re: Solar Powered Weather Station

    I have a weather station that uses 2 AA batterys and changed them about a week ago because I was worrying about them going dead over winter. They were 2 years old and the outside ones still tested strong. The inside ones showed a lower voltage than the outside ones. Mine is a lacross. Maybe you would only need to change batterys every couple of years. solarvic
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Solar Powered Weather Station

    Instead of replacing the AA batteries on my outdoor unit, I wired bigger D cells in series soldering the connections with a very hot iron/gun so the job can be done in an instant before it heats the batteries. It's almost a flash soldering job it's so quick that way, so the batteries aren't damaged. I put this battery pack in a water/weather tight container with a wee hole in the bottom to vent and drain any moisture that might appear, and they last at least 6 times longer than the AA size. A lot less hassle than designing and building a solar system, and might even outlive a solar/rechargeable battery system.
  • System2System2 Posts: 6,290 admin
    Re: Solar Powered Weather Station

    3 volts DC...


    Thanks for the responses and the suggestion about the D sized batteries... but, for a Solar and Wind forum, i dunno, i would expect a little more enthusiasm for the project as intended.
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Solar Powered Weather Station

    We are a practical and cheap bunch of folks here...

    One quick and simple way of powering your system... Assume 1 WH AAA batteries at 3 volts. And the system will run one year on a pair of AA batteries. If you assume you 100% recharge the batteries between 2 days (maximum of ~C/8 to C/10 current) and over 1 month, assuming 4 hours of sun per day, the amount of current would be, roughly:
    • 1 Watt*Hours * 1/1.5 volt per cell * 1/30 days to recharge * 1/4 hours of sun per day = 0.0056 Amps
    • 1 Watt*Hours * 1/1.5 volt per cell * 1/2 days to recharge * 1/4 hours of sun per day = 0.083 Amps
    So, roughly, you would want the current flow into a pair of AAA/AA batteries with an estimated 1 Watt*Hour of capacity and 1.5 volts for one battery or 3.0 volts for two batteries in series. Assuming that NiCad may be a better choice, but NiMH should work OK too...

    Normally, I would be recommending a lower voltage solar panel--say 6 volts, but you can use 12 volts too, just pick a different ballast resistor value.

    First, pick the min/max ballast resistor:
    • V=I*R; R=V/I
    • (8 volt Vmp solar panel - 3 volt batteries) / 0.083 amps = 60 ohm resistor
    • (8 volt Vmp solar panel - 3 volt batteries) / 0.0056 amps = 893 ohm resistor
    So, resistor wise, anything between 60 and 893 ohms would meet the 2 day to 30 day recharge cycle requirements for a fixed array getting around 4 hour per day.

    If you use a 6 volt panel (really Vmp~8 volts), the panel wattage would be:
    • Power = Voltage * Current
    • Power = 8 volts Vmp * 0.083 amps = 0.7 Watts @ "6 volt" solar PV panel
    • Power = 8 volts Vmp * 0.0056 amps = 0.05 Watts @ "6 volt: solar PV panel
    This is a simple, unregulated method of making the circuit. Current is so low, that you probably will not over-voltage the batteries or the weather monitor.

    Be aware that using a simple circuit like above with NiCad batteries in solar powered path lighting, the NiCad cells usually last about 1-2 years before wearing out.

    Also, many of the small path lights use inexpensive epoxy (or similar) resin potted thin film solar panels--Which probably also have a 1-2 year life.

    There are variations here... I used Ballast Resistors because you can use any panel over 1 watt @ 6 volts. Or even 12 volt panels over 2 watts just by changing the value of the resistors.

    If you get "exactly" the right Imp rated solar panel (>4 volts Vmp and Imp around 0.0056 to 0.083 amps), you could even dispense with the ballast resistors as solar panels are a "natural" current limited source (i.e., they can only output rated current and no more--unlike a typical battery which can output enough current to fry wiring).

    One thing you may try--Is many yard lights do use a pair of 1.5 volt AA or AAA NiCad batteries (~3 volts to power the 1 white LED) for their overnight power... People frequently toss the yard lights away after one to two seasons. You can get the lights, strip out the cells+circuitry (if any other than the On/Off sun sensor), repackage, and use it to recharge your weather station. They are designed to recharge in 1 day and should provide more than enough energy for your weather station which runs around 1 year on a full set of batteries (instead of 1 day).

    There are lots of other methods to recharge the batteries. Voltage and Current sources using 3T Regulators and such... Just depends on how deep you want to go into the project.

    You may even find some small solar cells, wire them up, and encapsulate your own array (roughly, Vmp~0.5 volts per solar cell).

    Is this more of what you were looking at?

    The reason for the D Cell battery answer--D Cells are, roughly, 10x the storage capacity of an AA battery... So, they should last upwards of 5-10 years between change outs in the system. A bit easier, less expensive, and possibly more reliable than a solar based recharger.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Solar Powered Weather Station

    adding to what bb said about us being practical and cheap, i am wondering why you would object to running a wire down the pole as the batteries could then be placed at a convenient place to be changed or charged if you prefer that route. even real cheap wire would do here as not much power would be needed to travel it. just be sure to add a tad of slack to the wire to keep stresses off the wire itself, but also support the wire to the pole in at least 3-4 places to prevent too much movement on the wire which could break it.

    as to using a pv with it, it was already said that it will not require very much in the way of power to run it. due to the higher voltages though it would need regulated downward and can be done with linear regulator ics if you are any good with electronics. the lm317 style is variable, but fixed regulators can be used too if you know how to manipulate them.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Solar Powered Weather Station

    NiCads can take a constant but light overcharge and just turn it into heat (slight warmth) without damaging the battery, sort of self regulates that way if used with solar that doesn't over power it's ability to handle that extra charge, making them ideal for solar pathway lighting. Not sure how NiMH handle overcharging - - - - did some research on them about 10 years ago for the local fire department, to compare with NiCad, and if I remember right, they needed a heavier charge rate than NiCads to do any good, (a low, trickle type charge didn't do a proper job) then have that charge current cut off when they're up on full charge. But that was 10 years ago, and we all know nothing stays the same.
  • sawmillsawmill Solar Expert Posts: 93 ✭✭✭
    Re: Solar Powered Weather Station

    I recently replaced an older ice damaged La Crosse system. The new unit had a small solar cell similar to the yard lights that BB mentioned. The instructions stated the solar cell was to extend battery life so time will tell. Seems that BB and Wayne have a solution to your situation.
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Solar Powered Weather Station
    adding to what bb said about us being practical and cheap
    One or two of the cheap solar night lights available at Walmart. Already have rechargeable batteries in them. Find a bigger one and use to power your weather station. Shoudn't cost more then about 12 dollars plus some tinkering to remove the LED and wire it into your weather station and mount the panels on the pole in direct sun.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar Powered Weather Station

    For what it's worth, I actually have a weather station that came with a small solar panel to keep the batteries for the sensor unit charged. It was sold under the "National Geographic" label, but I don't see them listed anymore. The solar recharging has never worked. The panel is too small, even with good insolation, and standard alkalines are not meant to be recharged anyway. NiCads would not power the sensor properly (Voltage too low - inaccurate readings) and I don't think there was much in the way of charge regulating; just the small panel with blocking diode to keep the batteries up.

    I only menton it to demonstrate that some systems like this are commercially available, but that doesn't mean they'll actually work (or at least not well). Concocting your own will require experimentation, but in the end you will know that it will work.
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Solar Powered Weather Station
    I only menton it to demonstrate that some systems like this are commercially available, but that doesn't mean they'll actually work (or at least not well). Concocting your own will require experimentation, but in the end you will know that it will work.
    The Davis Vantage Pro 2 series weather stations wireless sensors are powered by a small solar panel, and a supercap. For backup they use a small 3 volt cr123 lithium battery that need to be replaced about every 2 to 3 years.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Solar Powered Weather Station
    mikeo wrote: »
    The Davis Vantage Pro 2 series weather stations wireless sensors are powered by a small solar panel, and a supercap. For backup they use a small 3 volt cr123 lithium battery that need to be replaced about every 2 to 3 years.

    My uncle has one of those, his book says the 3 volt lith battery will run it for more or less 3 months without any sun at all, but up to 3 years with sun.
Sign In or Register to comment.