Hi!
If I would like to run a arduino straight from a solar panel this would mean that twice a day the board would receive less voltage than required but still voltage (everything from 0.1 to 2.5 if I have understood it right for the uno rev 3).
Would this be harmful for the board?
Would this in any way affect the performance or would it be business as usual once the voltage is high enough? Would it be a problem having the voltage differ from 2.6 to a bit over 20 over the day?
Best
Martin
The board is not guaranteed to boot up correctly if the voltage rises too slowly.
Use a "reset controller" IC to keep the board in reset until the panel voltage is high enough to power it. They are typically 3 pin ICs and are available in a wide range of voltages and other options.
Would it be a problem having the voltage differ from 2.6 to a bit over 20
The Uno can have a problem if the Vin voltage is above about 12V, as the regulator has to dissipate the excess voltage as heat.
Your best option is to use the panel to charge a battery, either lead acid, NiMH or NiCd, as those tolerate much more abuse that lithium-based batteries, and do not require sophisticated charge controllers.
Did you mean "brownout" - not "burnout" ?
You might find this solar powered Arduino project interesting. It uses a supercapacitor to power the Arduino at night.
Over 20 volts? Yes, that would be very bad. The power supply on the Arduino can only handle 12v. But when the voltage was below the brownout voltage, the board would shut off. If it is what is controlling the solar circuit, that would be a VERY bad thing to have happen. I would recommend that instead of powering directly from the solar, power from a battery and use the solar to recharge the battery. That way the Arduino gets nice clean power all the time.
Thank you for all the answers!
When thinking about it I knew 12 v is the recommended max and 20 v is the absolute max.
To continue, if I’m trying to stay away from batteries, is the a way, as with reset controller, to send everything above 12v to burn as heat or to run a motor?
If I would like to go with the battery-option and anyone has some nice does and don’t for a build that is to be placed outside where it can be between +35 C and -30 C sending temperature and humidity-updates every hour through 900 mhz adafruit radio it’s warmly welcome.
Best,
Martin
The best approach for powering Arduino from a higher voltage source is to use a switching buck regulator to directly provide 5V or 3.3V, bypassing the inefficient linear regulator.
That avoids the need to "burn" significant energy as heat. I strongly prefer this one.
Hi!
Thanks for all the great answers!
The question of why keep away from batteries is a good one - one that I don’t really have a good answer to.
Things that I have as arguments is that I live where the temperature goes from approx. -30 C in winter to +30 in summer and I’m not sure how the batteries will behave in that kind of cold.
Another one is that I had an idea that the application is only needed in day-time. It’s some sort of (a bit advanced for the actual need) pool-heat-managing device. It started out as a project to build a database with data to practice machine learning on and it has grown from there.
I have an idea of a set-up using relays.
0-5 v burn the energy to heat water.
5-15v a relay kicks in and the arduino is running.
15-24v a relay kicks in the the energy is burned heating water.
The thing is, how do I prevent the arduino from getting more than about 15v? Is there some sort of voltage-roof passage that could be used?
If I’ll use batteries, the 15-24v could be used to charge the battery and the use the eventual excess to heat water.
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On the same subject but in a different application I have another question, let’s call above for number one and this number two. 
If I would get for example two solar panels that gives 100w each during the best prerequisite that my location can offer during the best summer days.
All energy should be used to heat air.
So I have 200w during full summer.
In winter I’ll have perhaps 100 w.
Let’s say I get 8 heater at 25w each.
During summer it’s full blast on all of them - happy days!
But during winter I don’t want 8 lukewarm heaters, I want 4 really hot ones.
Is it the same here, that relays is the best option or is there a smarter way to get this working?
All values are just for example, I’m still at learning phase before I go in to actual calculations.
Thanks for all the help that I have received, this forum is great!
Martin
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