Solar Panel Charger For Arduino

Is it possible to connect a solar panel charger that has a output of 5.0V, 0.5A to a Arduino board that has a 14V battery with a step-down voltage regulator. And if so, how?

Magician: No problem, if it is 5V output you can connect it directly to Vin, instead of power connector jack.

That is just plain wrong. External power connector and Vin pin must have at least 7vdc to power the on-board +5vdc regulator correctly.

Magician, I've noticed you frequently give out advice and answers that are just not even close to correct. Perhaps if you read and study more you might gain the knowledge to give more accurate advice.

Maybe you don't understand the questions being asked correctly? Not meant to offend you, but it's just that most of your responses to posts are just kind of off the wall. Why is that?


You are absolutely wrong that Vin MUST to be more than 7V, nothing of the kind. What happened if you apply voltage less than 6V? Nothing, read how voltage regulater works, chip will just supply "at most" to the load, in this circumstances Atmega328 will get 5 - 1 = 4, that is good.

Have you studied the Arduno auto-voltage switching circuit. Tell me how the external power will be utilized by the arduino board if it's at 5vdc and if the board is connected to USB power to upload or monitor serial data. Notice the op-amp circuit on the arduino board, what is it's function and how specificaly does it operate?

Again you stated simply that one could apply a regulated +5vdc to the Vin pin. Is that still your opinion?

There are several ways to power an Arduino board, even applying regulated +5vdc right to the +5vdc pin, however the board is designed to operate a certain way under all conditions such as uploading, running, serial monitoring and being able to supply voltage to external components up to a certain current limit.

My main point was applying regulated +5vdc to the Vin pin is not such a way.

The Arduino 'official' specs for external power voltage is stated as: Input Voltage (recommended) 7-12V Input Voltage (limits) 6-20V


Magician: Yes, I checked it out.

OPA will turn down power from USB, if Vin more than 6.6V And what ? This switch works ONLY on USB power line. It has nothing to do with what we are discussing. Vin has no "interrupter switch" , if board is not connected to USB (that is the case)

this circuitry (OPA) is useless when you power board from Vin , it is comparator if you know what does it mean, and in my opinion you have know clue.

OK you win, +5vdc to the Vin pin is fine in spite of Arduino's board specification. I will go back to just ignoring your answers that I either don't understand or disagree with.


Magician: O'K, let have a piece. Power can go down as low as 3.7V, from formula: Vin(3.7) - dropout voltage(1.0) = 2.7 minimal voltage for 328p chip. There is a disadvantage in powering low voltage, as on board voltage regulate would not filter a noise from power line. It make sense to power low voltage (3.7 - 6.6) if the source is clean, like battery or supply with voltage regulator build in, most Switching Power Unit would be o'key.

analogRead() will require lots of fuzzing with to get any consistant readings? How much voltage required to maintain 16Mhz operation per Atmel specs?

Now, can this recharge the 14v battery or would I need to add something else?

Also, the voltage regulator is labeled SHDN, VIN, GND and VOUT. What gets connected to the 14v battery and what gets connected to the Arduino board (positive/negative)?


So, if I was using a step-down regulator so the Arduino ran cooler and connected the positive terminal of the battery to vin and negative to gnd. Where does VOUT and SHDN get connected to the Arduino?

@bnewbi, You have a stepdown regulator similar to something like this? with 14 Vin, 5V out. battery+ goes to regulator Vin, battery- goes to regulator ground and to arduino ground. Vout set to 5V goes to 5V pin on the arduino. This one has a SHDN pin, it can be used to SHutDowN the regulator if the battery voltage goes too low to prevent damaging the battery. Its specs say "If the voltage on the SHDN pin drops below 1.1 V, the regulator will turn off."

Now you want to connect solar panel 5V out in parallel with that 5v? I would add a transistor to the circuit to pull SHDN low when the solar panel was active so that you don't have the battery current trying to possibly overpower the solar panel output when it was active.

Need more info on your parts to offer more advice. Perhaps bringing in power from both together with a diode on each going to the 5V pin would be best. Arduino would see ~4.3V, but it runs fine on that. I have run mine on 3 AAs into the 5V pin, was still going fine when voltage had dropped down to 4.25V, and should all the way down to ~3.8V. And maybe past that, altho below that operation is only guaranteed for 8MHz operation. So you could use a 3.3V Promini instead; I have one running in an RF remote control powered from 3.7V LiPo battery that was putting out 4.1V last I measured it, draining veeeeery slowly from a full charge (draws 0.99mA in sleep mode).

What's your application?

Don't mix up the parts being used. Arduinos use ATMega328P-20PU (DIP) or -20AU (32 pin TQFN)

is the solar panel charger output(5.0v,0.5A) enough to charge the 14v battery when in sleep mode?

No way 5v will charge 14v unless you up the voltage with a switcher of some kind.


@bnewbi, Graynomad is right, you need some kind of boost regulator to do that. Such as this

Then I would mate it with battery charge control chip from Maxim to control charging. Can't recommend any particular device as you haven't indicated what the 14V battery is.

Go browse the possibilities, filtering of choices is available:

The 14V battery is a rechargeable Li-Ion.

14VLi Ion, I think is really 4 Li-Ion cells stacked up end to end, for example

So look for a charger chip that can drive that, hopefully one that will not need too many external components.

Thanks Crossroads, I appreciate the help.