Solar panel and electrical questions
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  1. #1
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    Default Solar panel and electrical questions

    I have a couple of those panels that are supposed to keep a 12v battery topped off when a car isn't being driven. I've not used them.
    It is very over-cast with typical wintery clouds today and my volt meter is showing that it is producing 18.49 volts of DC. We have a cabin that is off grid, and I've been wanting to set up some battery-operated lights, a fence charger, and other appliances.
    What will I need to do to set some things up?
    WayaCoyote

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  3. #2
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    Charge controller w/fusing, deep-cycle batteries, cables, DC breaker box, meters if you want to check charge/output, inverter or lights and appliances which use DC.

    What kind of amperage are you getting?

    MM

  4. #3
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    You'll need a setup something like this
    http://www.12volt.com.au/General%20H...iagram_eng.gif

    Basically you need a controller that you connect the solar cells and battery to,and it regulates the charging of the battery so it's not overcharged. And the controller ensures the output to your light, fence, etc. is 12V and not too high or too low.

    These controllers have a huge range of features (fancy charging modes, displays, etc.) and capacities, and a wide range of prices to with it.
    This looks like a fairly simple one to give you an idea:
    http://www.stecasolar.com/en/art/uid.../beetools.html
    Looks like the Steca PR 1010 version runs around $110 from various websites. I'm sure there are other suitable controllers out there.

    -Tim

  5. #4
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    Here's a simpler unit with similar capacity for about $55:
    http://www.affordable-solar.com/morn...ontroller.htm#

    There are a few different models depending on what your loads are:
    http://www.affordable-solar.com/sola...controller.htm
    There are a bunch of SunSaver models for various voltages and loads.

    -Tim

  6. #5
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    MM,
    How do I check the amperage with a multimeter? I checked the volts with the panel outside Not connected to anything...

    These panels are supposed to be "complete" for just trickling a car battery to keep it topped, but I was surprised at the 18.4 volt output. I guess the trickling effect comes from the Amperage?

    For my little cabin, I'm not going as far as a Real Solar setup yet. I'm just hoping to be able to run a couple of small lights for a while after dark. I'd like to use some LED's. I have some flashlights that run off of 3 AAA batteries. Is there anyway I could string them (series or parallel) to run off of a 12V car battery which would be recharged with these pannels?

    What little "experiments" could me and my 3 year old son do with them to explore electricity?
    WayaCoyote

  7. #6
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    To check the amperage you need the multimeter inline with the load. The voltage will drop with the load connected and you really don't want to measure amperage right across the terminal of the solar cell because you could damage it and it wouldn't really give a realistic reading anyways.

    Yes, the cells probably produce fairly low amps and would just slowly charge the battery. If it's low enough, you probably aren't going to overcharge the battery.

    You could string up 3 of these LED lights in series (so each one gets 4 volts). It's a little under what 3 AAA alkaline batteries would give, but more than 3 rechargeable batteries would yield, so it's probably safe. May want to put a fuse in the circuit to avoid any shorting issues.

    -Tim

  8. #7
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    An easier way to figure things out is to realize that current
    solar panel technology runs about 10 Watts per square foot.

    Now Watts = Volts * Amps, so if you are seeing a 15V to 18V
    output from a panel that is "trickle charging" a car battery,
    then you can conclude that you will produce less than 1 Amp
    at that voltage from the panel, which is reasonable for a
    "trickle charging" application, but is not enough current to
    recharge a battery that kept the lights on, ran the radio,
    recharged your cell phone, and did other "minimal" things
    you'd want a solar panel to do.

    So, off the top of my head, you need to check out solar
    panels that are capable of charging a deep-cycle marine
    battery with a "charge controller" gizmo riding herd on
    the whole deal.

  9. #8
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    If you have what I think you do, you are probably getting something in the range of about 300-400 mA. (1000 mA = 1 A or .3-.4 A) That given you will see about 1.2 to 2 A per day.

    So you can see that with that charger you are going to be in quite a deficit to have much of anything running from your battery(s). If you can manage that load for a short period, maybe a little LED lighting and then get off of it and allow the charger plenty of time to recover over some days then you could make it useful. It's not really designed to give a quick recovery from a load, just keep a battery topped off.

    But from your first statement, I don't think it's going to give you what you're looking for without help of more cells.

    Now if you got a creek up there with at least 10 feet of head on it? Whewhooo, now we're talking some horse power!!

  10. #9
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    Default

    Thanks, guys. All of this has helped answer lots of questions.

    Bizzy, we don't have the water yet, but we're looking for it! Wouldn't that give us something to work with!?!
    WayaCoyote

  11. #10
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    As for your cabin, if you are not there all the time, given the current cost-per-watt of solar panels, you'd be well off to build something that would hide them, because when you ain't there, someone's going to abscond with them.

    The technology itself is about to burst out of the gate however. Seeing the obvious, several very large high-tech companies are investing hundreds of millions in solar. Both in the panels themselves and computer-controlled circuitry. In fact, after the first of the year, I am being moved from desktop microprocessor design over to solar microprocessor and chipset design.
    Once you see the bandwagon, it's too late.

  12. #11
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    Default

    Quote Originally Posted by wayacoyote View Post
    MM,
    How do I check the amperage with a multimeter? I checked the volts with the panel outside Not connected to anything...
    You're not going to be able to measure large amounts of amperage (current) directly with the leads on a multimeter - do a internet search on "shunt" or "making a shunt to measure amperage" for more information. Basically, a shunt is a resistor device (a certain length of wire - all wire has resistance) to be placed in parallel with your current meter to be the load on which to then measure the voltage drop, and then you can calculate the current.

    Bizzybee is right - to bank a lot of amps in your batteries, you're going to need quite a few panels.

    MM

  13. #12
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    Most multimeters have a shunt built into them so measuring current isn't a problem.

    -Tim

  14. #13
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    Quote Originally Posted by tarheit View Post
    Most multimeters have a shunt built into them so measuring current isn't a problem.

    -Tim
    Yes - low amperage - higher amperage might fry inexpensive units, check to make certain that your input is fused -- use the high amp, fused jack and make certain that your meter will handle higher amperage.

    MM

  15. #14
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    i recently plugged one of these from harbour freight into a car and was impressed to have the radio go on. i unplugged it and sure nuff radio went off. this tells me that while the sun was shining you could have a radio on in your cabin with it. as far as the three year old is concerned if he had as much fun with it as this forty five year old had it would be worth it.
    cover the panel, uncover the panel, cover it half way, see if the noise just dims or is either just on or just off...
    when given star thistle make honey

  16. #15
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    harbour freight has a 45 watt solar kit for $199 walmart has 400 watt inverters for $25. with 2-4 batteries you can have sat. tv for 4-6 hrs a day and run your laptop.

  17. #16
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    Default DC Soolar

    Quote Originally Posted by wayacoyote View Post
    MM,
    How do I check the amperage with a multimeter? I checked the volts with the panel outside Not connected to anything...

    These panels are supposed to be "complete" for just trickling a car battery to keep it topped, but I was surprised at the 18.4 volt output. I guess the trickling effect comes from the Amperage?

    For my little cabin, I'm not going as far as a Real Solar setup yet. I'm just hoping to be able to run a couple of small lights for a while after dark. I'd like to use some LED's. I have some flashlights that run off of 3 AAA batteries. Is there anyway I could string them (series or parallel) to run off of a 12V car battery which would be recharged with these pannels?

    What little "experiments" could me and my 3 year old son do with them to explore electricity?
    Try one 75 - 150 watt solar panel, two 6 volt Trojan golf cart bateries, a fuse on the positive side of the baterries, and a small charge controller to prevent the batteries from over charging and to prevent your batteries from "leaking" electricity out through the solar panels at night. Add some DC lights and you should be in business.

    You do not want to lose over 5% of your electricity. 12 volts and 10 gauge wire will not carry electricity very far. Backwoods Solar has a neat table that I used to calculate wire size and voltage that I needed to keep from losing more than 5% of my power.

    http://backwoodssolar.com/
    Last edited by JC; 12-14-2007 at 10:18 PM.

  18. #17
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    You have a number of options for off the grid operation: Solar, Wind, Fuel Cell, Hydro, Generator, etc.

    There are a number of things to consider before taking on the expense of installing and maintaining a power generation system.
    What will your use of the cabin be?
    What type of load will you have? Lights , TV, Computers, Appliances, etc.
    What are your options to run your large power consumption items?

  19. #18
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    Default Solar Energy International

    You may be interested in a Solar Energy International (SEI) workshop on photovoltaics design and installation (http://www.solarenergy.org). I had two very knowledgeable instructors. One of the instructors was Scott Ely from Earthsense (www.earthsense.com), the educational division of Sunsense. Another student and I were the only two students who had working solar systems. One student said that SEI was a traveling salvation show, attracting more converts from the dark-side to a sustainable energy future!

  20. #19
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    Lightbulb

    I think this is what you were looking for;

    http://www.thefarm.org/charities/i4at/surv/spht.htm

    With this system you can use the little panel you have, charge the battery and have light from the Snakelight, or use any of the VersaPak tools.

    I found this back in '99 when making preparations for going off line.
    Bullseye Bill in The Scenic Flint Hills , KS
    www.myspace.com/dukewilliam

  21. #20
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    Same charger

    My deer feeder uses a PowerStar DE650-S 6Volt 5Ah battery
    My fence charger uses a X-Power Tank SB-604BC 6Volt 4Ah battery
    These are small batteries (not the type used on motorcycles)

    I tried charging one with a 6volt car battery charger. You know what happened. It melted the plastic. Can I charge them with my solar panel car battery trickle charger mentioned above?
    WayaCoyote

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