Solar Array and Lipo

[aerosacha]

Hi there, I'm a 3rd year Aeronautical Engineering student at Brighton University (UK) currently working on my dissertation, which is a solar powered model aircraft.

I am not the best with electronics so I apologise if I'm a little dense not the topic.

My aircraft will have an array of solar cells producing around 2.5A at 12V

I will be using a 3s Lipo battery 1100mah 11.1V

The motor will be drawing more power than the solar array provides, so how can I draw all the current from the solar array and the rest that is needed from the battery?
I was going to use a maximum power point tracker but as I will be using more power than I am producing I feel it is an unnecessary weight.

Any help would be greatly appreciated, as it is holding my project up but it is not an important aspect I am being assessed on due to being an Aero engineer.

Many thanks, Sacha.

 

[Harald Kapp]

Insert a LiPo charger suitable for your battery between the solar cells and the battery.
Draw all load current from the battery.
That way the solar panel will recharge the battery while the battery will provide the power to the load.
Note that you may have to provide a protection circuit to prevent the battery from deep discharge (this will damage the LiPo). This circuit will disconnect the load from the battery in case of too much energy draw from the battery. You may want to have a circuit that gves an early warning before disconnecting the load so you have time to land the aircraft safely.

Im not an expert on this kind of circuits, but I'm sure you will find ff the shelf components or hobby kits performing this task.

 

[Arouse1973]

Dont forget 3 Lipos in series will require 12.8 Volts for charging not 11.1V.
Thanks Adam

 

[aerosacha]

Thanks for your help, I have considered that way, charging the battery with the solar array, but I feel that it waste energy going through the battery rather than straight to the motor, is that correct? If i do do it that way then i have calculated I need a maximum power point tracker in order to charge the battery efficiently, which adds around 80g to my aircraft.
Is there any way for it to go straight to the motor and take some of the current from the battery or is that quite a complex system?
I think my ESC turns the plane off before the battery gets too discharged, but without a warning, it would be nice to have some kind of warning like you said
And to Adam, yea I haven't finished my solar array yet, I am going to add as many cells in series till i get 13V+ in realistic daylight conditions, thanks for reminding me.
Thanks, Sacha.

 

[Arouse1973]

Dont forget each cell needs a charging voltage upto 4.2 Volts.
Good luck
Adam