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  • alexlfm commented on JoshuaZimmerman's instructable $4 Solar Battery Charger3 years ago
    $4 Solar Battery Charger

    Sorry I missed that you have a 5v panel. In this case you may want to use either 4 batteries (which would never get fully charged but would come pretty close at 1.25v) or else consider using a resistor with at least 2 batteries. Remember R=V/I from physics? If you need a refresher see this page here: http://www.gtsparkplugs.com/Dropping_Resistor_Calc.html You do need to be careful though since the more voltage you are dropping, the higher the wattage resistor you need (in general, most resistors are 1/4 of a watt. For one battery ideally shoot for a voltage of 1.5, 3v for 2 batteries, 4.5 for 3 6 for 4, and so on.

    I would first make sure that you have the diode the right way round. Diodes do obviously only go in one direction and have a set polarity. The line on the diode always indicates the negative (out) end. The easiest way to check is to put a multimeter, set to the ma current range and then connect it in series between the diode and the battery pack with the red positive probe on the diode out side and the black negative probe going to the battery pack. The meter will read a positive reading in mA if everything is working correctly, which is how much power is flowing into the batteries. If you don't have a multimeter I would highly suggest getting one as it's really an essential tool and worth it just for checking batteries and basic repair/automotive uses; For basic dc, low voltage, use, t...

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    I would first make sure that you have the diode the right way round. Diodes do obviously only go in one direction and have a set polarity. The line on the diode always indicates the negative (out) end. The easiest way to check is to put a multimeter, set to the ma current range and then connect it in series between the diode and the battery pack with the red positive probe on the diode out side and the black negative probe going to the battery pack. The meter will read a positive reading in mA if everything is working correctly, which is how much power is flowing into the batteries. If you don't have a multimeter I would highly suggest getting one as it's really an essential tool and worth it just for checking batteries and basic repair/automotive uses; For basic dc, low voltage, use, they can be found quite cheaply at around $7 (I can recommend some if you don't have one). You can also short circuit the solar panel through a multimeter with just the diode and nothing else attached to it to get an idea of it's performance. Solar panels are one of the few things it's fine to short circuit. Unfortunately apart from a multimeter the only thing I can suggest is connecting an LED temporarily in series before the battery packs just to see if the panel is producing power (though if you leave the LED in it will burn out without a properly sized resistor).The other thing to keep in mind is that solar panels in general, although especially these smaller ones, are very sensitive to the angle of the sun and the output can go from maybe 100mA or possibly less laying flat on the ground to 200mA angled into the sun. This site has lots of detail on solar panel angles (and the effect on output) and was very helpful to me: http://www.solarpaneltilt.com/

    First of all, the blocking diode usually goes on the positive terminal of the solar panel going towards the batteries. Secondly, you are using multiple batteries correct? I completely disagree with this article, if you have a 4.5v panel you need to have 3 batteries connected in series to charge safely since each battery is 1.35v charged. With only two batteries on a 4.5v panel you are putting too much voltage on the batteries 4.5v on 2.6v max of batteries, and risk damaging them, especially long term. Over voltage destroys batteries. This is why most solar lights have 1.5v, or if they use two batteries 3v, panels.

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