Hi, I was wondering is it possible to run micro-controller constantly from solar panels inside flat near the window?
The issue is that during the day when its cloudy solar panels provide only 3V, but the "Solar Lipo Charger Board CN3065" expects input of 4.4V-6V.
Is 3.0 volts the open cell voltage? Or under load?
Is that 3V the open circuit voltage on a cloudy day? Did you measure it? If not, where did that number come from?
Also, you didn't say, but you also need a very low dropout 3.3V regulator for your STM. The panels may be nominal 5V, but that typically means they can put out close to 6V in bright sun.
Do you have any feel for how much current your circuit will draw when running? Will it be sleeping part of the time? That's going to be the biggest determinant of battery life.
I suggest to look for a different charger. Something that implements Maximum power point tracking (MPPT) . When using such a charger, you may want to put some solar panels in series, and have it step down the voltage instead.
I have measured 3V when solar panels were connected in parallel and connected to battery charger, but without connected battery itself and also without micro-controller connected. I will try to test voltage of panels without charger connected too.
Did not thought of that yet, but I would expect that charger also gives 5V "SYS OUT" (although I guess it will be 4.2V instead of 5V?) and micro-controller circuit would have 3.3V regulator itself.
I would expect that draw current of micro-controller would be in range of 20-50mA. And at night when its completely dark, it could go to sleep mode less than 1mA.
How about connecting solar panels in series (35V 50mA) and then using stepdown converter to create 5V and using same battery charger circuit? Would it be a better solution?
Hi, I was wondering is it possible to run micro-controller constantly from solar panels inside flat near the window?
I would expect that draw current of micro-controller would be in range of 20-50mA. And at night when its completely dark, it could go to sleep mode less than 1mA.
If the panels are not all facing in the same direction, there could be a difference in the output of the panels, and if there are no blocking diodes, then the overall OC voltage could be reduced. You might test the panels individually to see if the OC voltage varies.
In the final installation, will all seven panels be facing in the same direction, and all equally in sunlight, or all in shade, at the same time? If so, you probably don't need diodes.
There's no SYS OUT pin. The system is powered from the battery pin, and should be limited to 4.2V. Do you know what 3.3V regulator is used on the processor board, and what its dropout voltage is?
If there's any way to have it sleep, even for short periods, during the day, that would have a big effect on how long the battery lasts.
I have systems that use ~20mA peaks, when transmitting with radio to hundreds of meters in microseconds, and sleep for less than 5uA. 50mA to run a microcontroller is crazy high power nowaday.
I don't see what you gain from that. The seven panels in parallel will give you 350mA of charging current when the sun is out, with no conversion losses. Seven in series might give you some charge current when it's cloudy, but not very much. The panels simply can't generate much power in shade, no matter how you shift it around.
Yesterday was a sunny day, so during that time I have registered 5.2V for single panel. I have tested 7 panels and they still made 3.6V apparently it was too high on the window and half of the panels get shade, after moving them lower I have observed 4.9V, so I guess its quite similar to 5.2V of a single panel.
I don't know, but I have googled that its possible to supply the battery voltage to 5V pins of micro-controller and it still should work ok. I have tested it with charged battery and it works. So I think this is not an issue.
I would love to get any mA number from panels even in cloudy days, today is cloudy and charger does not seem to turn on... but Its quite bright outside so I would assume there is some current to harness?