Need help creating a solar charging circuit for hobby

In summary: Would this work?It has an output voltage of 8v and output current of 3.6mA. The low current worries me that it would restrict the charge. The solar panel has a max output of 50mA. would charging a 4.5 v circuit with an 8v booster hurt anything? Is this why I need the buck converter to bring the voltage back down to say 5v?This is a buck converter I found:http://www.linear.com/product/LT1076-5
  • #1
Jaron Wiley
4
0
Hi I am fairly new to electronics and I have a project I want to create a circuit for. I have a solar panel rated 6v 50mA. I want to make a rechargeable battery run a series of 2 or 3 bright LEDs.

My question is: What voltage limit will the source need to have in order to take a charge from a 6v solar panel? Will 1.5v batteries in series require greater voltage to charge?

and What components do I need to include in the charging circuit besides the panel. (can I just connect it directly to the battery?)
 
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  • #2
Jaron Wiley said:
Hi I am fairly new to electronics and I have a project I want to create a circuit for. I have a solar panel rated 6v 50mA. I want to make a rechargeable battery run a series of 2 or 3 bright LEDs.

My question is: What voltage limit will the source need to have in order to take a charge from a 6v solar panel? Will 1.5v batteries in series require greater voltage to charge?

and What components do I need to include in the charging circuit besides the panel. (can I just connect it directly to the battery?)

Welcome to the PF.

It sounds like a good project. Keep in mind that the output of the solar cell will vary, depending on the amount of sunlight hitting it ("insolation"). Because of this, the solar cell's output voltage may vary from above your battery voltage to below your battery voltage.

So the type of DC-DC converter you would use for this application is the SEPIC topology DC-DC:

www.ti.com/lit/an/snva168d/snva168d.pdf

Or alternately you could use a Boost DC-DC followed by a Buck DC-DC:

http://en.wikipedia.org/wiki/Dc-dc_converter

You will also probably want to put a diode in series with the output of your charger circuit, to keep from discharging the battery when the output of the DC-DC falls below what is needed by the DC-DC to make the charging voltage.
 
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  • #3
berkeman said:
Keep in mind that the output of the solar cell will vary, depending on the amount of sunlight hitting it ("insolation"). Because of this, the solar cell's output voltage may vary from above your battery voltage to below your battery voltage.

So the type of DC-DC converter you would use for this application is the SEPIC topology DC-DC [...]

You will also probably want to put a diode in series with the output of your charger circuit [...]
The solar cell output voltage is linearly dependent on temperature but only (indirectly) logarithmically to the insolation, so large temperature swings are a greater threat to a steady output voltage than varying insolation levels.

Considering his inexperience I think he would be better off following the KISS (keep it stupid simple) principle here and simply clamp his solar cells with e.g a 3 x 1.5V (4.5V) battery that would be in parallel with 2 x 2V(?) LEDs + a resistor. The series (Schottky) diode would still be necessary to avoid discharging through the solar cells. This approach has at least one glaring pitfall though; since the battery would clamp the solar cell, its output power would be at its lowest when the battery is discharged (when you need it the most), so it might be a good idea to throw in a comparator or something to prevent the LEDs from draining the battery too much.

In my mind this should work (albeit rather inefficiently), but my mind doesn't always work. What do you think?
 
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  • #4
berkeman said:
Welcome to the PF.


Or alternately you could use a Boost DC-DC followed by a Buck DC-DC:


I looked at the schematics for the SEPIC converter and I believe our friend is a correct that it is a little over my head. I understand the basics, I just have trouble with the equations (not knowing the desired values of Vd, etc.) Since this is just one part of a larger project I'm trying to finish by november I will try something more simple. I see the importance of having a DC/DC converter, so I will because I expect to have periods of low Vin. So in a follow up to Berkeman, Will this boost converter work?:

http://www.newark.com/diodes-inc/zxsc300e5ta/ic-led-driver-smd-sot-23-5300/dp/34M9011

It has an output voltage of 8v and output current of 3.6mA. The low current worries me that it would restrict the charge. The solar panel has a max output of 50mA. would charging a 4.5 v circuit with an 8v booster hurt anything? Is this why I need the buck converter to bring the voltage back down to say 5v?

this is a buck converter I found:

http://www.linear.com/product/LT1076-5

Note it says it "only 9.5 mA quiescent current." Does that mean it needs 9.5 mA input to work. Could it work with the boost above.

Im thinking: A series circuit 3*1.5v(4.5v) source to the solar panel to the boost to the buck (I'd like to discard the buck if I can use the 8v output) to a diode. Then I could create another series led and resistor circuit in parallel to the charging circuit. What do you think? I greatly appreciate your help!
 
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  • #6
To effectively charge a battery the Voltage and Current need to be well regulated - so this does depend on how long you expect this system to last. If you do not charge the battery properly it will not last long - and different battery technologies ( chemistry) like to be treated differently.
The LED is much easier however - a LED driver can probably be found that will run off of what ever Battery voltage you use.
 

1. How do I design a solar charging circuit for my hobby project?

To design a solar charging circuit, you will need to determine the voltage and current requirements of your hobby project. Then, choose a solar panel with a voltage and current output that matches or exceeds your project's requirements. Next, select a charge controller that is compatible with your solar panel and can regulate the charging process. Finally, connect the solar panel to the charge controller, and then connect the charge controller to your project's battery.

2. What components do I need for a solar charging circuit?

The main components you will need for a solar charging circuit include a solar panel, a charge controller, and a battery. You may also need additional components such as diodes, resistors, and capacitors, depending on the specific design and requirements of your circuit.

3. How do I choose the right solar panel for my hobby project?

To choose the right solar panel for your hobby project, you will need to consider the voltage and current requirements of your project, as well as the size and efficiency of the solar panel. It is also important to consider the environment in which your project will be used, as this can affect the performance of the solar panel. Do some research and compare different options to find the best fit for your project.

4. Can I use a solar charging circuit for any type of battery?

In general, you can use a solar charging circuit with most types of batteries, including lead-acid, lithium-ion, and nickel-metal hydride batteries. However, it is important to choose a charge controller that is compatible with the specific type of battery you are using. Some charge controllers may also have adjustable settings for different types of batteries.

5. How can I ensure the safety of my solar charging circuit?

To ensure the safety of your solar charging circuit, it is important to follow proper wiring and installation procedures. Make sure to use the correct components and follow the manufacturer's instructions. It is also important to regularly inspect and maintain your circuit, especially if it will be used in outdoor or harsh environments. If you are unsure about any aspect of your circuit, consult a professional or do additional research before proceeding.

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