So for my project I needed very low consumption, so cutting out the led, the inner tension regulator, and going into deepsleep whenever I could was the solution.
On top of that I use a 3W 6v solar panel. I couldn't find any working MPPT that would charge the battery with the solar current, so I directly connect the solar panel to the 3.7v lipo battery. It works great. But when the battery is full, it separates itself from the system. It means that the solar panel has no load anymore, and its tension goes from 4.2v to 6.8v. The step up (3.7v to 5v) receive that, does not transform it all apparently, and so the arduino is running at more or less 7v during the day.
I did not observe any damage.
Is it a problem to run the arduino at 7v ? Longterm damage ? basically during the day my arduino is just deepsleeping 2s and read a photoresistance, and then deepsleep again 2s and so on.
If you have the power connected to the Arduino 5V in pin, it is likely to damage it. Assuming it is a 5V board.
Could you please post an actual sketch of your circuit? And also the exact Arduino you are using.
Just checking the ATmega datasheet (which I have on my computer) it says the "absolute maximum" voltage is 6V. That doesn't mean it's going to blow-up at 6.1V or 7V but "you can't complain if it does".
I didn't look-up the other chips.
It's entirely up to you if you want to take the risk. I wouldn't go into production with something like that, but for a one-off hobby project the worst thing that can happen is you fry your Arduino and then you'll have to replace it (or the dead chip(s) and then you'll have to come-up with a different solution.
...I test some (non-Arduino) boards at work. They also have a 5V regulator than can be bypassed by moving a jumper. I have to test the voltage regulator so I don't normally bypass it and I like to keep the power supply at about 7V. These particular boards can always survive 7V when I've accidently had the jumper wrong. But at 12V the RAM chip will blow every time and sometimes the CPU and maybe the flash chip, but most of the 5V chips are OK after being over-voltaged to 12V,
Can you post a circuit diagram of your charging circuit, how are you disconnecting the PV when the battery is full?
An image of a hand drawn circuit will be fine as long as you include all power supplies, component names and pin labels.
It sounds like a language translation problem here, what do you mean by;
The step up (3.7v to 5v) receive that, does not transform it all apparently, and so the arduino is running at more or less 7v during the day.
The battery has its own internal self protection circuit against short-circuit, too low tension, and overtension. The overtension is set between 4.2 and 4.25v, basically a MOSFET just switch off, the battery can not receive current anymore, but it can deliver some.
For the step up, it transforms <5v into 5v, but if I applied on it any higher tension than 5v it won't get it higher at all.
At first I was using a 5.1v 5W zener diode as shown on the circuit so that when the battery is full the tension would never be higher than 5.1v (5.3v in reality). It works, but the zener diode got very very hot. Apparently at a temperature of 75°C it should withstand and dissipate 5W, the solar panel is around 2/3W max so I don't understand why the zener is so warm. Maybe it is just its normal behaviour...
If you apply voltage above 5.5V to a 5V Arduino chip, you will very likely damage it, or destroy it completely. Likewise for applying voltage greater than 3.6V to a 3.3V chip.
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