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Solar panel uses?? Answered

Hey guys I'm needing the expert opinions of everyone here in the tech section. See I just mounted this 0.5 watt solar panel outside on a L bracket today (not just a couple tiny ones I pulled out of solar lanterns (does anyone want to see what it looks like mounted outside? I didn't think to take pictures until I got inside).

Anyways, I've mounted it, ran the wire along the ground and in through my window (drilled a small hole below the window). Connectivity checks out good and I get about 20-21v and the full sun hasn't even hit it yet. The only thing is here though, this solar panel is meant as a trickle charging panel for car batteries and whatnot, and as such I only seem to be getting about 10-15ma (seriously wtf).

I just resoldered this charging board from a solar lantern I had laying around, however I have a couple questions.

I'm not entirely sure if this little board will handle the current/voltage (however it should as it's fairly low current from the solar panel)

I've rigged up the board mostly like it was inside the solar lantern except longer/stronger wires. I have a switch on the positive line of the batt+ to the board. I soldered some thicker wires to the SOL connections on the board. Now I've seen a few of these and some are rather simplistic control boards and some actually have a bit of circuitry to them. This one appears to have resistors to current limit the LED (would be good so I don't blow it), however after following the traces on the board the led get's it's positive from that black transistor thing with 5 legs on it (what is that a power regulator?)

The idea behind all of this here is that I can maybe charge up my cell with it or usb devices for example, but to have that come from a battery pack of AA's (to work as a buffer sorta-speak like a capacitor bank). I am a little miffled as how to make this work right the way I want it to. I would assume that once I get the battery pack situated I can disconnect the LED and use that connection for a charging cable, but then it would only provide power when theres no sunlight out (when you turn it on it turns the led on if there is no current coming from the solar panel).

How can I do this guys I'm sorry to ask such stupid questions as I know to some of you's it's probably fairly mediocre but I'm a bit dumb.


 Sorry for the second post ran out of space to put in the following references so you can learn how to change the circuit to fit your desires.




 Oh thank you! And yeah I think I need to get me a couple LM317's

 You might want to find a less power consuming controller than the LM317,ACTIVE COMPONENTS and ELECTROSONIC Inc. both have sites with cross referencing of semiconductors.They also have kits they will ship to you.   

That black dealy looks like a rectifier. It turns AC into DC.  And yes, you do need  it.

That's  what I thought, too.  I don't know.  That's just what it looked like to me.

 Yeah but what if the polarity reversed on the input?

That's what I thought too.  I was wondering, I see an inductor in there, is it possible is a small IC that acts like a joule thief or Minty Boost?  I thought it may be a transistor or two packaged together, because I do not see a LDR or Photocell, I thought the last leg may be connected to the Solar panel and used to turn the Joule Thief Circuit on only when its dark.

Another thought, it probably is a transistor, I have seen transistors that has 4 pins, usually a Collector / Emitter / Base1 / Base2, but I don't see why it needs another base pin...

 Yeah exactly, the guys above were probably right in saying it's a rectifier. Thanks for trying to help anyways man

Look on your so called rectifier to see if there are + ~ ~ - markings. Otherwise, I can't believe rectifiers are used in solar panel circuits.. :O

 Aye thank you, I've worked with larger rectifiers but forgotten what smaller SMD and through hole rectifiers looked like.


Sorry I have taken so long to get back to your post. It's city wide cleanup and I have been busy cleaning out my garage.....

First maybe I can clear-up some of the comments you have gotten. In looking at the photo you posted the part on the right side with the black wire is almost certainly a Shottky Diode being used to block current flow. I can see the part marking 5819. The diode should have 1N5819 if you can see the rest of the part marking.

Next the circuit you have here is designed to supply from 20 to 50ma @ maybe 3 volts. It should not be enough to charge your cell phone. Without modifying the circuit and doing some reverse engineering it won't do much more than power the LED and/or charge the batteries that were used in the lantern.

As you may recall you wrote that you cell phone require 4.75 volts @ .55amps. Well technically while the supply can supply .55amps that does not mean that the phone requires that much to charge.

The good news is that if you supply 4.75 volts to the phone the phone will regulate the charge to the phone battery and charge the phone. It will use as much current as it requires. Presumably less than the .55amps the wall adapter can supply. Otherwise the wall unit would burn up, possibly with smoke and flames. Really.

I have up loaded a drawing of a simple circuit you can make with a few dollars in parts. The LM317 will accomplish a couple of your goals:
1. The power supply output is variable from 1.2 volts to over 25 volts with 27.5 volts input. 2.5 volts is required by the regulator to regulate.
2. with the two fixed resistors switched in the output will be around 4.74 volts close enough to use in your phone charger.

Hook up your solar cell to this circuit be sure to get the polarity correct and you can charge your phone from the output or switch the switch and the output can be varied, up to about 19 or 20 volts, provided your solar cell is outputting enough voltage.

I would caution when charging batteries. Every battery technology requires a specific charge profile. Charge the battery to fast and you have an explosion and fire on your hands. 

You may ask why I chose two resistors on the one side of the switch. Resistors come in common values. So to get close to the specific value required I used two resistors.

When the two resistors are switched in the circuit the output voltage will be set to charge your phone. Switch the switch prior to plugging in your phone.

By the way all the resistors are 1/4 watt. Also use a double pole double throw (DPDT) switch so both switches switch at the same time.


8 years ago

Well, it probably won't like having 20V forced through it.  And, as far as I know, the whole circuit is intended to only charge a single 1.2V Ni-cad battery.  Not exactly what you're looking for.

The circuit you've got does not have a light sensor, because it uses the solar cell itself as a sensor!  When the voltage output from the solar cell drops below a certain threshold, it stops charging the battery and instead allows the battery to power the LED.  That's the job of that weird four-pin thingy on there.  Most likely, it's a pair of transistors packaged in a single case.

So, what do you need to charge a bank of AAs?  Well, this might do it.  There are far more complicated charger circuits out there (check out Linear Technologies' website for a large selection of battery charger ICs) but this one should work.


8 years ago

if you use the darker solar panels you are going to get more voltage vs. current. This also great for sunny days and it will have longest life without degradation. These are known as mono crystalline modules. Then for what you are looking for is a module that can produce a descent amount of current and voltage. The answer would be amorphous or thin film which has a brownish color and is generally cheaper. The life is so-so but in return you get a better overall power characteristics. The thin film will allow for a much larger current  in lower lighting conditions like a cloudy day. Try these out, walmart is selling the small solar lights for 3bucks and they have the battery, charging circuit and also a great module for good current for quick charging. Hope this helps...

 Ok ok I getcha, so what if I were to collect say for example, 100 of these solar lanterns, if I wired all the solar panels together in say, parallel, would I be able to do something useful with them all?

 As a rough answer to the lights with no LDR in them they probably switch at some threshold, using the solar panel as the detector of how light it is, when the charging drops below a certain level it swaps to powering the LED with the battery, rather than charging the battery... 

These ones seem much more prone to flickering near sundown I've noticed, going between the two modes...

 Yeah that seems likely, I wonder if it's possible to adjust the threshold. Flicker might be an issue for some but I haven't even noticed it.

The little black dealy (round one) is a diode and it prevents current from the battery from flowing into the solar cell when it's dark

From your explanation it is not clear what you are trying to do.
I doubt this circuit is a joule thief. One of the comments mentioned not seeing a LDR (Light Dependent Resistor) or photo cell. If this came from a solar lantern then it was connected to a photo cell and the IC in the picture is more likely a regulator / switch designed to control the charge current to the batteries. The switch side turns off the LED when the sun returns so the batteries can charge.
If you want to charge your cell you will need to regulate the voltage & current from your photo cell.
By the way your cell is producing .315 watts (= 21 volts * 15 ma) you said that the full sun had not hit yet so you may yet get the full .5 watts. Its also possible the photo cell has degraded a little since it was new.
In order to help you further you need to let us know more about the requirements of your phone. If you have a wall charger it should have the output voltage and current listed on it. Your regulator should mimic those values.
Good luck on your project.

> One of the comments mentioned not seeing a LDR ( L ight D ependent R esistor) or photo cell. If this came from a solar lantern then it was connected to a photo cell and the IC in the picture is more likely a regulator/switch designed to control the charge current to the batteries.

You're correct in the fact that it doesn't have an LDR. But the solar lantern did not have a photo resistor, as you will see in the photo I just took. There was just a battery, a solar cell, and that circuit board in the entire unit, No Photo cell. I'm curious as to why they do or don't use photocells in all solar lanterns. Some I see do have them and some don't. I think the ones that don't have them merely turn the led on when it doesn't detect power from the solar cell. If this does the same thing as having a separate device to tell it when theres sun out and when there isn't. Why not do it that way then?

>From your explanation it is not clear what you are trying to do.

I apologize I suppose I wasn't entirely clear, but I was looking to make some actual USE of this board and use it to charge up a couple AA energizer NiMh batteries I had laying around or possibly connect a battery pack of said AA's and use the board to charge a cell phone via the output the board has for the LED?

>The switch side turns off the LED when the sun returns so the batteries can charge.

Actually the switch only seems to be to shut it off when it's being stored in the winter, the solar panel switches the LED off when theres sun out, or I've noticed if there is no battery connection to the board, the LED comes on, but shuts off whenever I connect a battery to it, thus charging. Theres about 3-4v coming out of the battery wires with no load except the LED is on.

I found it neat that hooking a computer fan up to the battery cable made the led flicker as it spun, but now it won't run the fan, it was spinning nicely for like 5 minutes and I came back in the room and it stopped but the led was still on. I'm guessing just the sun outside going under a cloud or something but it's pretty damn bright out today.

>By the way your cell is producing .315 watts (= 21 volts * 15 ma) you said that the full sun had not hit yet so you may yet get the full .5 watts. Its also possible the photo cell has degraded a little since it was new.

Wow awesome that sounds about right. I think I might want a little more wattage though for something useful for charging a cell phone right? And yeah it is possible it has degraded, I "borrowed" it off this lady I know as she had bought it for a motorcycle her bf is building her, yet it's been months and he is still not completely building a motorcycle not much bigger than a gas scooter. Regardless it's just kinda ironic, so anyways it had been sitting there for nearly a year anyways. That wouldn't have made it degrade that much would it?

>If you have a wall charger it should have the output voltage and current listed on it. Your regulator should mimic those values.

Right you are, let me go look. Ok the output says 4.75v @ 0.55A. Personally I'd like to build something with an adjustable regulator, or a switchable setup to switch between multiple regulators.