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  • second hand panels

    Hello all, I just have a quick question for anyone out there that can help me out, I went to a garage sale and a gentleman was selling 2 solar panels they are not real big panels i think they are 85 watt each but i thought i could wire them up to my outhouse on my recreational property which has no power ran to it, i thought if i put a couple 1157 led bulbs in there there would be enough light for the odd time the wife has to go out and use it.. I am not even sure what panels are worth as i have never really thought i would ever use them for anything . Any ways i bought them for 20 bucks a piece thinking if they work for what i want good and if not i am only out 40 bucks, anyways not even thinking to ask the guy anything about them before i left, when i got home i realized that there are no wires on them there is a box on the back but no wires... so i took the box apart and sure enough there are connections for wires inside, but instead of just a positive and a negative there are 3 terminals and i have no idea what is positive or negative, so my question is if i can somehow upload a picture onto these forums do you think someone could help me out and take a look at it and lead me in the right direction?

  • #2
    Your bigger problem is needing a battery to run the bulbs and a charge control to charge the batteries
    from the panels. Before that you need to see what the panels are capable of, if they are good. With
    the terminals exposed in some good sun, use a voltmeter to find the 2 terminals that give the highest
    voltage, this is your Open Circuit voltage. Connect a short across the terminals and measure the
    current (I use a clamp on DC meter); this is your Short Circuit current. From that info you might start
    to design a system.

    Or just use a rechargeable flashlight, you might match the panels to it. Bruce Roe

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    • #3
      Great info ty bcroe, like i say i will try and upload a pic, it did come with a charge control. There is also a sticker on the back that gives all the info about the panel, i just wasn't sure about the connections and was afraid to hook something up wrong, but i never even thought about the dc meter i will give that a shot when i get back home on a sunny day.
      Here is the info on the back of the panel
      Max power: 85w
      Operating voltage 17.2 v
      Operating Current 4.9A
      Open circuit voltage 21.6V
      short circuit current 5.5a
      Last edited by Diablo846; 05-18-2017, 06:53 AM.

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      • #4
        One of our battery Gurus needs to recommend equipment to match, assuming the panels test good. Bruce Roe

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        • #5
          First thing and might be beyond your ability is to perform this test. It is a simple Voc and Isc test. That will tell you if the panels are good or not. It is simple but requires a good DVM which I doubt you have. They cost around $50 for bare bones minimum Chi-Com models.

          If they are good comes the bad news. Well not that bad, just some more pain pain in the wallet. Assuming they are good you will need a 10 amp PWM controller and a 12 volt 100 AH battery. A decent 10 amp PWM controller can be had for $20 to $25. and a decent 12 volt 100 AH battery will run you $90 to $110 and last a couple of years. Plenty to run LED lights and charge cell phone and laptop if you have a 12 volt adapter like a USB charger for the cell phone and 12 volt power brick for a laptop. An expensive toy to play with that turns on a light.

          FWIW if the panels are good, you got a decent deal. You paid roughly 25-cents per watt. New those same size panels cost 10 times that much. Problem is even if they are free are expensive to use. Batteries get expensive every replacing them every couple of years. At this scale a Kwh will cost you $2, your utility only charges 10 to 15-cents for that same Kwh for all you want. Here is the kicker. A 12 volt 100 AH battery has roughly 1 Kwh of energy in them, but with your panel wattage you can only use 20% or 200 watt hours of that power in a day. About 2-cents worth of electricity.

          On the other hand if you drink a lot of beer, just collect your farts. That is a lot more energy than the panels can generate in a day. Additionally will save planet earth by burning off that nasty methane gas you nasty filthy human. Only nastier animal is a cow and horse. So as a member of the Green Mafia shoot all the cows and horses until you run out of bullets. Save the last bullet for yourself. mother earth will thank you for it.
          Last edited by Sunking; 05-19-2017, 01:17 AM.
          MSEE, PE

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          • #6
            Wow this is awesome help guys i thank you so much u have no idea, i am working out of town right now but when i get home i will post a pic of what is inside that box, and i do have a multi meter i think that is what u were talking about. I dont mind spending the money on a few things just because i have no power line going to anything out there right now i am hoping to get all that dug into the ground next year.. but it is nice to hear that i actually might have gotten a deal on something if they actually work, and if they don't work i guess it will be time to bust out the beer lol.
            Thanks again u guys for all your help

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            • #7
              Originally posted by Diablo846 View Post
              i do have a multi meter i think that is what u were talking about.
              You are welcome. That meter will have to have a 10-Amp measurement capability, and you must know how to set it up to measure voltage and current. To measure current requires you to move the test leads to the Current Port.

              The example below demonstrates what I am talking about Voltage is taken with the leads in the Red Voltage Port and Black Com Port. For current you move the RED Voltage to the Black 10-Amp Port. Com does not change. You must also have the Selector switch in the correct position. So make damn sure you know what you are doing


              MSEE, PE

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              • #8
                Originally posted by Sunking View Post

                You must also have the Selector switch in the correct position. So make damn sure you know what you are doing.
                For example; Don't try to test the amperage of your battery, whether intentionally or by accident, thinking you're testing voltage, usually fatal to the meter.

                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                • #9
                  I just about never wire a multimeter into a circuit to measure current, too many problems. One alternative is
                  use a clamp on ammeter, DC here. Another is install a shunt resistor (very low value resistor) and measure
                  the voltage across it. Bruce Roe

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                  • #10
                    Originally posted by bcroe View Post
                    I just about never wire a multimeter into a circuit to measure current, too many problems. One alternative is
                    use a clamp on ammeter, DC here. Another is install a shunt resistor (very low value resistor) and measure
                    the voltage across it. Bruce Roe
                    I agree if you are talking about a working system. However for a panel string or panel to to Isc test no danger of any damage even if you have the leads and selector set wrong. You can short out a panel all day long with no issues

                    MSEE, PE

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                    • #11
                      alright guys i have uploaded a picture of what is behind the box on the back of the solar panel, i understand the negative black wire and the positive red wire, but what the heck is the yellow wire and why is the black attached to it with resistors behind that, and i am guessing there is some reason for the pen markings on the terminals? and yes sun king i have the same sort of multimeter, it is not a fluke but same idea
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                      • #12
                        Originally posted by Diablo846 View Post
                        alright guys i have uploaded a picture of what is behind the box on the back of the solar panel, i understand the negative black wire and the positive red wire, but what the heck is the yellow wire and why is the black attached to it with resistors behind that, and i am guessing there is some reason for the pen markings on the terminals? and yes sun king i have the same sort of multimeter, it is not a fluke but same idea
                        Those are not resistors, they are diodes. They allow the current to bypass a partially shaded segment of the panel, helps prevent hot spots that can damage the panel.
                        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                        • #13
                          Those are not resistors, they are bypass diodes. Now make the measurements. Bruce Roe

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