12V solar Charger Project I'M STUMPED! Please educate me!

[robertk445]

Ok Thanks in advance if someone can give me some clarity!

I am working on a project to understand this solar game. I thought I was super mechanical but just can't seem to get this thing done!

I have a 12v 1.5watt solar panel from Harbor freight. I cut it down slightly to fit my project. I cut off 6 of the 31 solar cells. Instead of the Vmax of 17V I now get around Vmax of 13V in full sun. by the number panels left I calculated that I have 1.16watt (1.5 watts / 31 cells * 24cells remaining.)=1.16W But I do not know how to confirm this! I have a great mutimeter.
I have one meter of LEDs (60 Leds, 2.4watts/meter) rated at 4.5V I have 4AA rechargable batteries at 4.8V (1500Mah) I would like to design a circuit that charges by day, illuminates the leds at night.

I understand that I need a blocking diode. Could someone please help me with this design? And better yet, to understand it?

Robert

[daz]

I cut it down slightly to fit my project. I cut off 6 of the 31 solar cells. Instead of the Vmax of 17V I now get around Vmax of 13V in full sun.

You cut your solar panel 'down' to fit your project???! You can't do that! You buy a solar panel with the correct physical dimensions to fit your project, not the other way around!

I have a 12v 1.5watt solar panel from Harbor freight.

Well.....you no longer have that any more....

by the number panels left I calculated that I have 1.16watt (1.5 watts / 31 cells * 24cells remaining.)=1.16W But I do not know how to confirm this! I have a great mutimeter.

You cannot do that to work out the power in a solar panel. Power is equal to voltage times current. So the way you trying to work out power, will not work. By cutting your solar panel, you have cut off about 25/30% of your power!

I have one meter of LEDs (60 Leds, 2.4watts/meter) rated at 4.5V I have 4AA rechargable batteries at 4.8V (1500Mah)

Why didnt you just buy a 6V panel? That can charge those batteries, and wouldnt have required any cutting...
To start with, a 1.5W solar panel may run your strip light for max 1 hour per day, as that size solar panel is waaaaaaaaay too small.

I would like to design a circuit that charges by day, illuminates the leds at night.
I understand that I need a blocking diode. Could someone please help me with this design? And better yet, to understand it?

Just use a voltage regulator, like a LM317, and set it to the voltage that you require. I have built lots of regs with that chip, and it works well. Plus, it has minimal parts count, so it shouldnt be too complicated for you to put together. Just pull up the datasheet for the LM317, and most of them list a basic schematic that you can use!
Blocking diode is not necessary when using the 317, as that is all internal for you.

[robertk445]

Getting closer one step at a time!

Daz Wow thanks for a quick response. My project requires a specific size panel that is why I cut this one down. Since the chips are stacked in only one direction, it was easy to use a glass cutter and cut off 6 of the 31 rows. This panel seems to yield more power then other types that I have tested. If my project is a success, I can have the panel made specifically to this size but I don't think it is possible to get more power given the required foot print. The voltage drop was as expected from the panel. From my understanding the panel should be rated avg of 1.5 times your battery. I was using 6AA and charging with same panel and batteries were maintaining good charge. I use 1 meter of 12V Led rated at 4.8Watts/meter. so that is why I switched to 4.5V leds and 4 batteries to hopefully get even better results?

I guess I need to know what the performance of this panel is. How do you measure the amps accurately?

Thanks Dax!

[SunEagle]

Daz Wow thanks for a quick response. My project requires a specific size panel that is why I cut this one down. Since the chips are stacked in only one direction, it was easy to use a glass cutter and cut off 6 of the 31 rows. This panel seems to yield more power then other types that I have tested. If my project is a success, I can have the panel made specifically to this size but I don't think it is possible to get more power given the required foot print. The voltage drop was as expected from the panel. From my understanding the panel should be rated avg of 1.5 times your battery. I was using 6AA and charging with same panel and batteries were maintaining good charge. I use 1 meter of 12V Led rated at 4.8Watts/meter. so that is why I switched to 4.5V leds and 4 batteries to hopefully get even better results?

I guess I need to know what the performance of this panel is. How do you measure the amps accurately?

Thanks Dax!

The best way that I know is to use a DC clamp on meter. Once the panel is connected to a load you can measure the amperage on either the supply (+) or return (-) wires.

[daz]

How do you measure the amps accurately?

You have to options;
1) you can do as Suneagle says and use a clamp on meter, or
2) you can use an inline ammeter (ie digital multimeter, lab ammeter, etc)

Those two will be your best options for getting accurate measurements!

[Mike90250]

Be advised, the raw edges you cut off the panel, will allow moisture in and ruin the panel over time. Panels are very hard to seal well, you have to seal out water VAPOR, not just fluid.

[robertk445]

OK I almost GET IT!

Thanks SunEagle and DAZ
Here is the update, I followed the advice and ordered and 5V 2.5W Mono panel. at 2.5W I can charge 2500mA per day. My usage should be with 1 full meter of leds = .157A
157mA * 8 hours =1256mA 50% draw

Is this looking better? Now my next step is to draw a wiring diagram and get a board made. I want to run the lights at night and off during the day. I think I need a blocking diode?
I have no idea how to draw this diagram, can anyone assist.

Also I have two choices for batteries. a 3.7 Lithium Ion rechargable OR 3AA 1.2V for 3.6V NiMH Will these batteries work the same or is
one different then the other. I cant thank you enough, I am finally making some progress!!!!: biggrin1:

Thanks again for any help!

Robert

[inetdog]

Thanks SunEagle and DAZ
Here is the update, I followed the advice and ordered and 5V 2.5W Mono panel. at 2.5W I can charge 2500mA per day. My usage should be with 1 full meter of leds = .157A
157mA * 8 hours =1256mA 50% draw

Is this looking better? Now my next step is to draw a wiring diagram and get a board made. I want to run the lights at night and off during the day. I think I need a blocking diode?
I have no idea how to draw this diagram, can anyone assist.

Also I have two choices for batteries. a 3.7 Lithium Ion rechargable OR 3AA 1.2V for 3.6V NiMH Will these batteries work the same or is
one different then the other. I cant thank you enough, I am finally making some progress!!!!: biggrin1:

Thanks again for any help!

Robert

To keep the lights from turning on during the day and wasting your battery and panel power you need more than just a blocking diode. A commercial solar charging and lighting controller will do all of those things for you. And if you have a good knowledge of electronics you can build a board to do same thing for only twice the cost. But it is not something that you can easily wire up from a wiring diagram we could provide to you.

Do not use any Lithium rechargeable battery unless you are using a commercial charger which is designed for that battery type. The dangers of explosion (excuse me: spontaneous rapid disassembly) and fire (excuse me: venting with flame) are too great. NiMH are a lot more tolerant but still require a well designed charger.

Your project to learn more should probably be designed for a commercial solar lighting controller and a small (~20AH) flooded cell lead acid battery instead.) But to do that will require a bigger panel.

If you are going to try to do something with the 2.5 watt panel and a few LEDs, I recommend that you get a few (~3) NiCad batteries instead, since they are very tolerant of overcharge, and then use a simple two or three transistor circuit to turn off the LEDs when there is voltage coming from the panels.

At 2.5 watts and 5 volts, you will get 500ma, or about 2500mah per day, since you will have at most 5 hours of full sun equivalent. If you get a 5,000 ma set of NiCad batteries, there is no way that your panel can damage them through overcharging, and just letting the LEDs run from the time the sun goes down till the battery runs down or the sun comes up should work just fine.

[robertk445]

Thank you Inetdog! Almost Complete solar Charger!

Inetdog Thank YOU! I am glad you posted that because I was leaning towards the flaming blow up batteries! I will focus now on NiMH. It looks like if I want to make the panel just a bit smaller and produce only 2 Watts, then I will still be in good shape with 4000mAh. I think 5000mAh would be hard to find at Walmart! so thank you for confirming that. You said you had a circuit design? Can I please get that?
I need to have a board produced. I spent part of yesterday trying to find a circuit but I just don't have command of the components to know which is the right one. Could you please post the circuit that would work for me? I like the method of turning off led when sensing voltage. I will actually have a board produced from one of these mail order companies. I need a very compact 30mm x40mm max board size.

I have to say it is really exciting to actually see something come together. So thanks for your assistance.

[russ]

spontaneous rapid disassembly and venting with flame

Love your description!

[inetdog]

spontaneous rapid disassembly and venting with flame

Love your description!

I picked them up from Candlepower forum.
Also got some other rather laughable circumlocutions from Boeing's PR responses to their LiCo battery problems.
My favorite there (paraphrased): "Although the event involved what some would call thermal runaway at the cell level, or even at the battery level, we properly say that there was no thermal runaway because there was no thermal runaway at the aircraft level."
In other words, since the whole aircraft did not catch fire and burn to a pile of ashes, there was no thermal runaway.

[inetdog]

You said you had a circuit design? Can I please get that?

I think I said that it would be easy to put together a circuit. But I do not have a design myself and I have not looked for one on the net. Sorry....
I would not be comfortable sending you a circuit unless I had tested it myself.

[robertk445]

Please Help I need working diagram for 5V 2W Solar charger!

Thanks Inetdog I really appreciate All then input.

HELP! I am looking for a diagram for my project. This is not my area of expertise. I need a board that is sustainable and efficient. Please Please give me a hand. The system now: 5V 2.5 W Mono Solar Panel. (3) 1.2V AA NiMH for 3.6V I will light up LEDs at night that draw .157A at full charge. I need 2 4pin micro connectors on the board to carry power to LEDs Perhaps there is a service that someone can recommend. Thank you for your help again in advance!!!

Robert

[PNjunction]

The project at this point is way too complex and not efficient on either the solar or nimh charging side.

I'd back up and rethink it and simplify.

Nimh AA charger - get one that can handle DC input and will charge each cell individually especially since you are charging an odd number of cells. Although no longer made, these are still available, work well, and are inexpensive:

Duracell CEF23AU charger. It will do both DC and AC input, AND charges cells individually. Made for the Australian market, it comes with a slide-on adapter for US markets (or should). Since you are wanting a DC input, this is not an issue. I have one - works well. USB output is limited to the old standard of 500ma max. Don't burn it out with a tablet that draws more. Personally I don't use the USB port.

Now that you know you can efficiently charge your AA's, work on the solar side. Simple - 5-10 watt panel. 5-7ah agm battery. Morningstar Sunguard 4.5 charge controller. Attach the Duracell charger to the battery. Done.