DIYWAMH

February 17, 2008 1:24 PM

Working on DIY solar charger from modified garden power lamps. Of course the panels look different than the ones in the pictures!

I am working on modifying those garden solar lights into a solar panel charger like shown in these two DIYS

Of course now that I have the solar panel completely taken off of the lamp it doesn't look anything like the solar panel in the above picture instead it looks like this.

I can see the two edges where the lamp was wired before and I have been soldering the wires to it and trying to run the lamp via the sunlight. No luck so far. I've also tried reversing the wires in case I got the positive and negative parts screwed up. Any suggestions to continue? Do I need different solar panels? Would it be a problem with the solder instead? (the solder did seem rather weak and popped off rather easily)

As you can tell, I don't do wiring for a living. Let me know if I'm missing relevant information in this question (questions relevant to the wiring not why do you want to do this or why don't you just buy a solar panel, etc)

posted by aetg to sports, hobbies, & recreation (6 comments total)

one thing to consider is that the output current of that cell may be too low to run the lamp directly.
usually there are 2 AA batteries in the circuit that charge all day from the low output solar cell. when it becomes dark the batteries kick in and supply the actual power to the lamp.
(and those batteries discharge after about 2 or 3 hrs, in my experience).
posted by The_Auditor at 1:41 PM on February 17, 2008

Good point, I guess I'll have to connect it to the battery and see if it charges up over time. This would all be a moot point if I had a volt detector thing. I don't really want to buy one for this project, but maybe I could borrow one somewhere.
posted by aetg at 2:09 PM on February 17, 2008

yep, you may find a multimeter useful. it measures voltage drop (E) , resistance (R) or current flow (I), depending on how you set it. you may want to measure the current (I) coming out of that little
photovoltaic cell.. (ohms law: I=E/R ..lots of fun there.)
posted by The_Auditor at 3:14 PM on February 17, 2008

After writing all of the below, a better idea came to mind. One way or another the solar lamp you have is harvesting enough energy to charge whatever batteries are inside it -- why not re-purpose the entire power system, not just the panels? You could possibly disconnect the lamp's batteries from the bulb/LED and connect them directly to your radio.

Meanwhile, here's the harder version:

A multimeter may be your best friend here -- you need to find out if the panel you have comes close to the specs of the one they used in their Instructable (~4V, 80mA).

The easiest way to measure those is with a multimeter. Set the meter to the right voltage scale (this is usually "20V" on the dial) connect the leads to the two contacts on the panel (alligator clips work well for this), and set the solar panel out on the sun. You should see about 4V (or -4; that's fine too and just means you've got the red wire on the negative side of the panel).

Then switch the meter to current mode (on most you have to move the probe from one socket to another), hook it up to the panel again, throw it in the sun, and see how much current you get (they expect .08 amps).

If you come up short on either number you're probably in trouble, but you need voltage more than you need current -- a fully charged pair of NiMH AA batteries is going to have a voltage of about 2.7V; if you use the diode in the Instructable you need another .6V for a total of 3.3V. If your panel is below that number then you have no chance of fully charging the batteries without extra circuitry. If you're reading zero then you probably haven't found the right connection points on the panel, or need better solder joints.

Just for completeness's sake, I'll mention that for NiMH rechargeable batteries, the 80mA panel they use would take something like 25 hours of sunlight to fully recharge -- here in New England that's at least a week.
posted by range at 8:03 PM on February 17, 2008

Since you've already said you don't want to buy a multimeter (or 'Volt detector thingie', if you prefer... ), you can detect current by just taking apart a cheap flashlight and touching one wire from the panel to the threads of the lamp, and the other one to the black-ringed terminal on the end. If it glows, you've got juice.

Now, the part that worries me was: (the solder did seem rather weak and popped off rather easily) - If that picture on flickr is your panel, you might have wound up ripping the attachment points off the panel. Take a careful look around the edge near where you popped off the terminals and see if there are thin wires running around from the front.
posted by Orb2069 at 9:41 PM on February 17, 2008

You really need a multimeter, but..

Detecting current without a meter will probably work better with an LED than a flashlight bulb. Yes, you will have to check polarity, but it takes much less current to create visible light.

While I have not played with solar panels, I have found that soldering to certain electrode materials can go very badly. In one case recently, I could get just enough hold to test a circuit, and then the wire would pop off. It turned out that each time I did this I was pulling a bit of electrode off of its substrate, and the solder bond itself wasn't a problem. It must have been the added mechanical stress I was causing, or a weakened bond caused by the heat of soldering. I think I decided to give up on the project, though I can't remember exactly what it was anymore, so who knows :P
posted by Chuckles at 10:50 PM on February 17, 2008