Solar cell battery charging (in a overly complicated project)

[adamWest]

Hi all!
Im building a light controller for my bike, to handle turn indicators, brake lights, position lights and so on, and im concidering adding a solar cell to the project, so i dont have to remember to charge the battery..

The light controller project is based on a arduino nano, using a couple of mcp23007 pin extenders to tidy up the cable installation (from 16 wires in a ratsnest down to 4 in a Y harness).
The arduino is powered thru a self-disconnecting circuit (held connected with D13 = high, on with a momentary button) and the arduino also controls the other modules in a similar fasion, turning off parts that arent used (to minimize current leaks)
The whole system (including the lights) is powered from a central battery, currently a 5v cellphone power bank (mobile charger).

there are some power banks available at the local electronics store, with a builtin solar cell and charger on the side of the battery casing, and im thinking of adding one of those, to my project.
A battery monitoring circuit would be added to poll the voltage levels (possibly thru resistor voltage dividers) using arduino analog pins.

The idea is to measure the powerbank and the main battery, and if the main battery is low and the powerbank is (close to) full, then charge the main battery off the power bank battery.

There will be some low drop voltage regulators between the battery and the rest of the electronics, so a slight over-current will be fine (i belive my regulator can handle up to 26V, im planning on 2 or 3-cell lipo).


I did purchase some lipo charger PCB´s off ebay, i havent tested them or investigated them so i honestly dont know how they work (story of my life), but in worst case; im not afraid of building one, as long as i can find a schematic.



I have already some of the project PCB´s populated and completed, but the main card is currently being re-designed due to incompetence the first time, so i figured lets add all those bells and cup-holders that got scrapped on the initial PCB design..


So, does that battery charging idea sound valid somehow, or am i a idiot for not realizing it myself?
And does anyone have ideas of how to do it, or how NOT to do it?
Im not skilled in electronics AT ALL, just barely able to understand electrical schematics and im googling pretty much everything, but im not afraid of a little challenge, i mean, this is´nt rocket-science..
So if anyone has a torch, im a wee bit lost in the dark, even tho i might have ideas...

 

[Irv]

Overcomplicated may be correct Could this whole thing run from a suitably-sized power bank? You can probably find a more efficient/powerful solar panel to charge the bank than the one which comes as part of the combo from the local store.

 

[adamWest]

Hehe yes, its a bit over the top to be honest.. but on the other hand, its ment as a base to grow in, to allow for future upgrades, like e-motor and electronic gear deraillours..
And most of all, its a reason for me to learn programming and stuff, so the more complicated i can make it, the more i will learn, at least thats the plan..

I did make some (initial) calculations, according to all the spec sheets, if i would turn on ALL LED diodes at the same time, it would consume some 2.5Amps @ 5V...
On the other hand, that includes the trailer, with its extra floodlights and a full set of lights, both front, rear and side lights, on top of the full set of lights on the bike itself and a floodlight that would shame some motorcycles.. (2x cree xm-l t6)

So a more real-world MAX would be somewhere around 1.5A @ 5V, and around that in average while blinking like a cristmas-tree even with the trailer (on "normal" amount of lights, no trailer front lights, work lights and so on).

But on a normal daytime cruize, it should be around 20-250 mA @ 5V, depending on what the arduino is up to..

 

[Irv]

There are many solar-cell equipped power banks (Amazon, etc) that have 2x or 3x 2 amp 5 volt outputs. Any of those should do, provided the total output isn't limited in some way.
IOW, I wouldn't fool with the LIPO's until and unless these power banks fail to work.
The added complexity and 2-way conversion losses wouldn't help.

Related to this, I think the power bank would be the better choice because I could take it into the office or house to recharge during the day, so it wouldn't get stolen and would have a full charge when time to ride home.

If you want the Arduino to continue to run during the day when not riding (theft alarm, perhaps?) then one of those little $5 tubular phone chargers from the dollar store will run a Nano for several days.

 

[adamWest]

Well, the thing is i dont leave my bike outside, its ether on the balcony (6th floor), next to me at work or under my arse.
And about 4 nights a year, its stored inside the fore-tent while camping.
..You see, its my precious..

So a fixed solar cell is my way to happyness, a piece of hardware that will never be forgotten somewhere, so one less thing off my mind.
And thats just the reason why i want a solar cell, so i dont have to remember to charge it, or remember to bring it with me when i go out biking.


I was actually considering running the project from a solar powerbank for a while, but somewhere along the way i decided against it, probably for no good reason what so ever..
I might be misunderstanding things, batteries arent my main field of research, but can i still use the power bank while its being charged by the solar cell?
In that case, its a no-brainer, i will have only a solar powerbank.




Regarding trusting powerbanks over anything, the question is rather trusting your own known and measured hardware over "made-in-china" mystery box with power leads..
Ive opened some cheap chinese electronics and i would NEVER leave a solder joint looking like many of the ones ive encountered.
Im not saying that all powerbanks are bad just because ive found bad solders in other electronics, im just saying that i prefer to open them up and inspect them before i would use them with anything expensive..


Its still ways to go before i order the rest of the stuff, but i humbly thank you for your input, its always helpful to have someone else look over a project!


..But now ive started to think about a anti-theft alarm..... thank you good sir, your great tip just stole my nights sleep..