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  • Output of Solar Garden Lights from the Big Box Stores

    Hey, I am looking to do some small solar projects and I was wondering if I can just buy some of the garden lights at walmart and use the panels on them.

    Has anyone tested the milliamp output of any of them? I'm looking for a combination of panels that can charge a 4.8V battery pack which power a small 2x3watt Class D amplifier. I only need about 20-30 minutes of use on the amp a day - its a portable speaker for my bathroom - the back of the speaker faces a sunny window - just enough power to keep the battery topped off with 2 10-15min showers daily (fiance and I).

    If the walmart panels are complete garbage is there a panel out there that would be a good match for this battery pack?

    The battery is "4.8V 2000mAh Square Receiver NiMH Battery Pack" I dont want to post links as a new member.
    The amp is: VMA2012 Class-D Audio Amplifier Evaluation Module (EVM) Board - its easy to google.

  • #2
    Easy Peasy. Forget the landscape light. Since you have NiMh battery you can safely charge them with a constant current of C/10 indefinitely. So just buy a standard 12 battery panel that has a Isc of around .2 amps, which should be about a 5 watt panel.

    Connect the battery directly to th epanel with a diode in series with either polarity of the panel to prevent discharging the battery at night back through the solar panel.
    MSEE, PE

    Comment


    • #3
      Thanks for the quick reply, two other questions come to mind then.

      Space is limited - the speaker box will only be about 10" tall and 6" wide - if I buy a 9v panel thats only 300mah - is that going to be a problem?

      Im going to look up some of the terms you used.. c/10 and isc and learn me some solar goodness.

      Im eyeing this panel: http://www.siliconsolar.com/9-volt-3...-p-501643.html

      Is it Ok to be charging while it discharges?

      Comment


      • #4
        Originally posted by MtnXfreeride View Post
        Space is limited - the speaker box will only be about 10" tall and 6" wide - if I buy a 9v panel thats only 300mah - is that going to be a problem?
        Nope close enough

        Originally posted by MtnXfreeride View Post
        Im going to look up some of the terms you used.. c/10 and isc and learn me some solar goodness.
        All C/10 means where C = the battery capacity expressed in Amp Hours. Your battery is rated @ 2000 ma or 2 amps. 10 or any number is the charge rate of 10 hours, or ho wmuch current is required to fully recharge a discharged battery. So to find the amount of current required to recharge a battery in 10 hours all we are doing is factoring out th etime element to leave us the current. A = AH / H, so 2 AH / 10 H = .2 amps.

        Isc = Current Short Circuit of a solar panel. Which means assuming the panel is exposed to 1000 wh/meter squared insolation input is th eamount of current will produce when shorted out at the panel output.

        Originally posted by MtnXfreeride View Post
        Is it Ok to be charging while it discharges?
        Yes
        MSEE, PE

        Comment


        • #5
          THis is a really easy question - but for some reason no one online who answers it gives a simple answer.

          Which way does my diode go?

          The diode descriptions states the cathode end has a stripe... I dont know what that means in terms of which way current can travel.

          So, if the panel is going directly to a battery, is the stripped end facing the panel or battery?

          Im trying to figure it out with my multimeter but its reading a voltage either way the diode goes and while it measures current with it only in one direction the milliamp rating goes down when I cover the panel. BUt flipped it only reads 0.

          Comment


          • #6
            Originally posted by MtnXfreeride View Post
            THis is a really easy question - but for some reason no one online who answers it gives a simple answer.

            Which way does my diode go?

            The diode descriptions states the cathode end has a stripe... I dont know what that means in terms of which way current can travel.

            So, if the panel is going directly to a battery, is the stripped end facing the panel or battery?

            Im trying to figure it out with my multimeter but its reading a voltage either way the diode goes and while it measures current with it only in one direction the milliamp rating goes down when I cover the panel. BUt flipped it only reads 0.
            Put it on the positive lead of the panel with the stripe end towards the battery. I like simple answers to.

            Comment


            • #7
              Originally posted by MtnXfreeride View Post
              Which way does my diode go?.
              You do not need to know. If it works, it is correct. If not, reverse it. No harm either way. That is as easy as it gets. But the stripe or Cathode end faces away from the positive polarity of the battery. Picture is worth a thousand words.

              MSEE, PE

              Comment


              • #8
                Originally posted by MtnXfreeride View Post
                Im trying to figure it out with my multimeter but its reading a voltage either way the diode goes and while it measures current with it only in one direction the milliamp rating goes down when I cover the panel. BUt flipped it only reads 0.
                That tells you. The diode should be conducting when the panel is producing current. It is when you put the diode the first way, it is not when you flip the diode. The first way is right.
                Your multimeter is showing a voltage either way because the diode will leak a very small amount of current in the reverse direction, and your multimeter is not a heavy enough load to pull that voltage down.
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

                Comment


                • #9
                  Power Test

                  Originally posted by inetdog View Post
                  That tells you. The diode should be conducting when the panel is producing current. It is when you put the diode the first way, it is not when you flip the diode. The first way is right.
                  Your multimeter is showing a voltage either way because the diode will leak a very small amount of current in the reverse direction, and your multimeter is not a heavy enough load to pull that voltage down.
                  A DVM is good for precision measurements, but not always best for sorting power connections. It will give
                  false readings on normal leakage or static charges. For a long time I have used a small light bulb to sort
                  out these things. It won't give a false reading, and demonstrates that some power is really there. It
                  can charge or discharge capacitors, and won't allow enough current to damage anything. I got called to
                  sort out a lot of phone stuff with a 48V bulb, while the confused DVM guys watched.

                  Here is the one I made for my array, works great. Uses 4 bulbs 120V 70W in series, same wiring
                  rules as 600V meter. A couple LEDs in the base show which lead is more positive, if I need to know.
                  It is useful from 120V to 480V. Bruce Roe PVTstLt.jpg

                  Comment


                  • #10
                    Originally posted by bcroe View Post
                    ...Here is the one I made for my array, works great. Uses 4 bulbs 120V 70W in series, same wiring
                    rules as 600V meter. A couple LEDs in the base show which lead is more positive, if I need to know.
                    It is useful from 120V to 480V. Bruce Roe
                    Nice, do you have a schematic of how you wired the LEDs to manage the voltage range ?

                    Why use 70w bulbs , why not the little 15W bulbs. 15W not enough load sometimes ?
                    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                    solar: http://tinyurl.com/LMR-Solar
                    gen: http://tinyurl.com/LMR-Lister

                    Comment


                    • #11
                      Bulbs

                      Originally posted by Mike90250 View Post
                      Nice, do you have a schematic of how you wired the LEDs to manage the voltage range ?

                      Why use 70w bulbs , why not the little 15W bulbs. 15W not enough load sometimes ?
                      Chose your wattage for the application. The 70W bulbs draw about 1/2A (and were
                      very available), used to test an 8A PV string. My 12V & 48V bulbs are far smaller.

                      A couple big LEDS are simply in parallel, but opposite polarity. I think I used a 10W
                      8000 ohm series resistor to each input lead. Like the incandescents, LEDs will respond
                      to a wide range. Bruce

                      Comment


                      • #12
                        Originally posted by bcroe View Post
                        .....A couple big LEDS are simply in parallel, but opposite polarity. I think I used a 10W 8000 ohm series resistor to each input lead. ....

                        Wow, most LED's have a very low reverse voltage spec, but I guess the one in conduction keeps the reverse voltage down. So you use 2, 8K resistors, with the parallel LED's in the middle?
                        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                        solar: http://tinyurl.com/LMR-Solar
                        gen: http://tinyurl.com/LMR-Lister

                        Comment


                        • #13
                          Tester Components

                          Originally posted by Mike90250 View Post
                          Wow, most LED's have a very low reverse voltage spec, but I guess the one in conduction keeps the reverse voltage down. So you use 2, 8K resistors, with the parallel LED's in the middle?
                          Your analysis is exactly right. I went out and took off the cover; the 2 series resistors are
                          each 6000 ohms, 10 watts. That totals 17 watts at my array unloaded peak of 450V. Not
                          really much concern for short measurements times. That is about 37 ma for the LEDs which
                          are medium power level (sunlight you know), but they still output at far lower voltages. And
                          of course those bulbs are 75W (cheap). Case is plastic like a meter for safety, still looking for
                          a plastic cover to complete that goal; bulb socket external plastic shields also. Left over from
                          some outdoor motion detector lights; I use many detectors usually driving only one bulb.
                          Probes & wires from a broken meter. And why such an odd bunch of parts? After half a
                          century in electronics, you just look around, and build with whatever is on hand.

                          It was really cool working on my 6 strings of 360VDC MPP. Find a pair, observe polarity, put
                          a test lead on ground and check every wire for any possible grounded current. Much quicker
                          than waiting for a digital display to settle down; useless on the ground test.

                          Bruce Roe

                          Comment


                          • #14
                            replied to a thread

                            Interesting, a sales link is removed immediately, but not before the
                            new "reply to a thread" with link message has gone out. Bruce
                            ++++++++++++++++++++++++++++++

                            Here is the message that has just been posted:
                            ***************

                            Comment


                            • #15
                              Originally posted by bcroe View Post
                              Interesting, a sales link is removed immediately, but not before the
                              new "reply to a thread" with link message has gone out. Bruce
                              ++++++++++++++++++++++++++++++

                              Here is the message that has just been posted:
                              ***************
                              I have noticed that sometimes I get an email when someone posts on a thread I have already posted but when I open the thread there is no new post.

                              So I figure a Moderator has dumped the entire new post including any offending links. Probably the right thing to do but it can be annoying when I take the time to look and find nada.

                              Comment

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