# Source for small 12V 1-2A solar panel charger / controller?

#### spinnaker

Joined Oct 29, 2009
7,835
I have been trying to get this solar panel charger / controller working and it is giving me nothing but grief.

I don't want to build one just go out and buy a charger (it is for our home owners association).

Can any one point me to a source small sized (less than 4" x 2" x 2") 12V 1-2A solar panel charger / controller? Hopefully low cost.

I searched everywhere but can't find one. Most seem to be several amps an expensive.

I found this one which is almost perfect except it is 6v.

#### SgtWookie

Joined Jul 17, 2007
22,210
Do you need the solar panel AND the controller?

Or just the charge controller?

#### spinnaker

Joined Oct 29, 2009
7,835
Just the controller for now. But I just went out for a bike ride and it gave me a chance to think.

Maybe I will build one?? What I have always hated about this light is that it always came on too soon. It monitored the voltage from the panel and if it dropped beyond a certain voltage, the light came on. There would still be plenty of daylight but the light was on.

So on my ride, I was thinking. Why not a PIC controlled solar panel controller??

I could regulate the voltage with an off the shelf voltage regulator. Use the A/D inputs to monitor the panel and the battery.

I could have lots of options like light on delay, light on duration, battery level light off, input voltage level to start the light on timer. Maybe over kill but it would be a interesting project and a practical one at that.

If I really get things rolling then I can add a servo motor and get the thing to track the sun!

Does this sound feasible? I understand these PICs are pretty low power. But are they low enough to not shorten my charging life too much?

Seems like it would be fairly easy. The only hard part (for me) is the switching transistor to switch the light on and off but I am sure I could figure that one out. If not I know this forum where there are some really smart people that know a whole lot about electronics.

#### Bernard

Joined Aug 7, 2008
5,555
3A controller,2.53x1.78x1.05 in.12V, CAT# SCN-1, allelectronics.com About $17. Last edited: #### SgtWookie Joined Jul 17, 2007 22,210 Just the controller for now. But I just went out for a bike ride and it gave me a chance to think. Maybe I will build one?? What I have always hated about this light is that it always came on too soon. It monitored the voltage from the panel and if it dropped beyond a certain voltage, the light came on. There would still be plenty of daylight but the light was on. You could change that to be controlled by a CdS LDR (light dependent resistor). Building your own charge controller can get pretty involved, especially if you're going to be building a maximum power point tracking controller. You really need a solar panel that is rated for about 12v, 10w. This gives about 834mA at peak output. Your tiny solar cell won't do anywhere near that much, even if it were brand new. So on my ride, I was thinking. Why not a PIC controlled solar panel controller?? I could regulate the voltage with an off the shelf voltage regulator. Use the A/D inputs to monitor the panel and the battery. I could have lots of options like light on delay, light on duration, battery level light off, input voltage level to start the light on timer. Maybe over kill but it would be a interesting project and a practical one at that. If I really get things rolling then I can add a servo motor and get the thing to track the sun! Does this sound feasible? I understand these PICs are pretty low power. But are they low enough to not shorten my charging life too much? PICs have a "sleep" mode. They draw very little power when asleep. They can be programmed to sleep for milliseconds or many hours. Seems like it would be fairly easy. The only hard part (for me) is the switching transistor to switch the light on and off but I am sure I could figure that one out. If not I know this forum where there are some really smart people that know a whole lot about electronics. A logic-level MOSFET would likely be the easiest way to turn the light on and off. Look at the charge controller that Bernard posted. It looks promising. Thread Starter #### spinnaker Joined Oct 29, 2009 7,835 You could change that to be controlled by a CdS LDR (light dependent resistor). The box is encased in the light. I'd hate to have to drill a hole for the resistor. Could I just not just use the panel? Or do you have a suggestion on how I could mount the resistor? Building your own charge controller can get pretty involved, especially if you're going to be building a maximum power point tracking controller. Tracking will be version two or maybe version 3 (or maybe version Never ). Version 2 , I figure I could just adjust angle based on the day of the year. I have read about how the angle of the panel should be adjusted (manually) at least four times a year based on your location. OK forget tracking for now. I figure I have three things I have to monitor. Input from the solar panel. I would think that would be pretty easy. Then there is the battery. The two parts I am unsure monitoring for overcharge and undercharge. I would think undercharge could simply be handled by shutting down the light when the battery voltage reaches a certain level. I would think overcharge is more complicated because the regulator is charging the battery. You really need a solar panel that is rated for about 12v, 10w. This gives about 834mA at peak output. Your tiny solar cell won't do anywhere near that much, even if it were brand new. My panel is 11" x 35". Here is a 12V 10W and it only measures 12" x 13". Granted it probably has newer technology. One of my settable options would be to shut the light down after a few hours. I don't need it to run all night. running down the battery. PICs have a "sleep" mode. They draw very little power when asleep. They can be programmed to sleep for milliseconds or many hours. A logic-level MOSFET would likely be the easiest way to turn the light on and off. Look at the charge controller that Bernard posted. It looks promising. So I could put it to sleep and wake it up say every 30 minutes to check status. That is what I was already thinking. Last edited: Thread Starter #### spinnaker Joined Oct 29, 2009 7,835 3A controller,2.53x1.78x1.05 in.12V, CAT# SCN-1, allelectronics.com About$ 17.
Thanks Bernard! Seems to be what I need. Maybe will will buy this to get the light up and running now. The only thing I don't see is if it monitors sunlight level to turn the light on (should have put that in my requirements).

If this works, I could then work on my PIC controlled light if I can get the details worked out. And if it doesn't work out we always have the

#### spinnaker

Joined Oct 29, 2009
7,835
I think I might go with one of these . I think it is obvious these folks know a bit more about charging batteries then I currently know.

Of course that does not mean I can't work on my own charger project.

The only problem is that this charger is a bit too large for my current enclosure, which is the light itself. I did not like that enclosure anyway. It is already too tight. Can anyone recommend a source for water tight enclosure big enough for the battery and charger?

Battery: 3.5" W 4"H 2.75 "D
Charger 1: 5.24" W 2.75" H 1.31" D
Charger 2: 7.5" W 3.5"H no depth specified

#### SgtWookie

Joined Jul 17, 2007
22,210
Those charge controllers require vertical mounting, and airflow.
You can't put them in a closed box. They are for indoors operation only.

Futurlec is very quick to charge your credit card when you place your order, but it may take over a month for your shipment to arrive, and communication with them is difficult as English is not their primary language. Ask me how I know this.

The only reason I ordered anything from them is that they happened to have MAX038's in stock, and everyplace else I checked has been out of them for years.

#### spinnaker

Joined Oct 29, 2009
7,835
Those charge controllers require vertical mounting, and airflow.
You can't put them in a closed box. They are for indoors operation only.

Futurlec is very quick to charge your credit card when you place your order, but it may take over a month for your shipment to arrive, and communication with them is difficult as English is not their primary language. Ask me how I know this.

The only reason I ordered anything from them is that they happened to have MAX038's in stock, and everyplace else I checked has been out of them for years.
OK Note to self: If you are to remain in good standing on the AAC forum, at least make an attempt to read the datasheet!

Actually in my defense only the 3rd one mentions mounting instructions. Why does it need to be mounted vertical?

My search continues I guess.

Thanks for the warning on the company!

#### SgtWookie

Joined Jul 17, 2007
22,210
Actually in my defense only the 3rd one mentions mounting instructions.
That's the only one I read, because it's the only one that seemed to somewhat match your requirements.

Why does it need to be mounted vertical?
Airflow. The ventilation holes are in the bottom and top panels. If you don't mount it vertically where it can get good airflow, it burns up.

If you put it in a box with no airflow, it burns up even faster.

#### spinnaker

Joined Oct 29, 2009
7,835
I did not realize the position would make that much difference in airflow.

But my simple little light and battery under charge should not draw all that much anyway. Correct?

Is there some place I can learn about heat dissipation requirements as it relates to power? Obviously an important part of the design and sounds like an interesting topic too.

#### SgtWookie

Joined Jul 17, 2007
22,210
I did not realize the position would make that much difference in airflow.
It's the design of that particular controller. Since it needs so much airflow, you can figure it's not very efficient. If something is getting hot, it's dissipating power - power that might have otherwise been doing something useful.

But my simple little light and battery under charge should not draw all that much anyway. Correct?
I already told you what current you needed to charge your battery, and what the minimum recommended charge time was for a fully depleted battery. I haven't changed my mind.

Is there some place I can learn about heat dissipation requirements as it relates to power? Obviously an important part of the design and sounds like an interesting topic too.
You might be more interested in efficiency. Power in vs power out. The difference relates to the efficiency of the device. If the power out is significantly different than the power in, the power consumed in the device will be dissipated as heat.

#### Bernard

Joined Aug 7, 2008
5,555
Extrapolating from my 6" X 11" , 1W panel, yours might be about 6W peak & 600mA. Have you measured short ckt. A & open circuit V ? What is the rating of "your" lamp? Where is the reverse current diode located.

#### spinnaker

Joined Oct 29, 2009
7,835
Extrapolating from my 6" X 11" , 1W panel, yours might be about 6W peak & 600mA. Have you measured short ckt. A & open circuit V ? What is the rating of "your" lamp? Where is the reverse current diode located.
Thanks Bernard. Location of the reverse current diode is unknown. I do not have a schematic. Looks like the board is fried anyway.

Rating of lamp is unknown but it as an array of 18 x 6 large white LEDs .

I guess I could measure open circuit current, then measure with array connected and figure it out from that?

#### SgtWookie

Joined Jul 17, 2007
22,210
Here, get one of these:

A 10 Ohm resistor. RS only sells them in pairs, but that's OK. Just use one of them.

Short your multimeter leads together on the lowest Ohms setting (probably 20 Ohms)

Measure the resistance of the resistor using your multimeter. Record the reading.

Then connect just the solar panel's leads (without the charger board) across the resistor.

Then set your meter to the 20v scale or higher.

Take the panel/resistor assembly outside in the sunlight and record the voltage reading you get across the resistor - at various times of the day in bright sunlight.

This will give us a good real-world indication of the current capabilities of your solar cell.

Until you can provide us with that information, we're just kind of spinning our wheels.

#### k7elp60

Joined Nov 4, 2008
562
If you use a PB137 IC it will work great as a charge controller. It is a 3 terminal regulator designed to be a charger for 12V batteries. The quescient current with no load is only about 4mA.
I have one mounted on a TO220 heatsink and I just tested it with a varying load from about 25mA to 2.0 amps. The output was 13.7 volts and no current limiting until about 2.0 amps.
I have attached the PDF file.
I have mine mounted on 1/2 of a Radio Shack 276-159 proto board. I drilled some holes to mount the 1 inch high heatsink.
I have some extra PB137's, send me a PM with some shipping info and I''ll send you one.

#### Attachments

• 86.5 KB Views: 19
Last edited:

#### SgtWookie

Joined Jul 17, 2007
22,210
The PB137 is a linear regulator.

It's basically the equivalent of an 78xx regulator that's set to a fixed output voltage of 13.7V.

During daylight hours, it won't charge the battery at a decent rate, and will basically throw away 2.1v to 2.6v of the solar cell's output due to it's Vf.

#### k7elp60

Joined Nov 4, 2008
562
The PB137 is a linear regulator.

It's basically the equivalent of an 78xx regulator that's set to a fixed output voltage of 13.7V.

During daylight hours, it won't charge the battery at a decent rate, and will basically throw away 2.1v to 2.6v of the solar cell's output due to it's Vf.
That is true, but for simplicity and cost I think it's pretty good.

#### spinnaker

Joined Oct 29, 2009
7,835
Here, get one of these:

A 10 Ohm resistor. RS only sells them in pairs, but that's OK. Just use one of them.

Short your multimeter leads together on the lowest Ohms setting (probably 20 Ohms)

Measure the resistance of the resistor using your multimeter. Record the reading.

Then connect just the solar panel's leads (without the charger board) across the resistor.

Then set your meter to the 20v scale or higher.

Take the panel/resistor assembly outside in the sunlight and record the voltage reading you get across the resistor - at various times of the day in bright sunlight.

This will give us a good real-world indication of the current capabilities of your solar cell.

Until you can provide us with that information, we're just kind of spinning our wheels.
OK everything sounds really easy except for one item. A sunny day.
I hear we are supposed to get one Sunday.