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Solar cells, batteries and motor

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halvorlu

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I'm working on a project to build a (mainly) solar-powered boat. The boat will also have a battery for storing energy, and (naturally) a motor for propulsion. Additionally it will contain some electronics for turning the motor on/off, turning the rudder and so on.

What I've found challenging is to design the circuitry to connect the solar cells, battery and the loads (i.e. motor, electronics). The solar cells will have a peak power of about 30W-40W. They will probably give a voltage of about 8-9V, and currents up to ~5A (or 4-5V, ~10A). The battery voltage is not yet decided, but it may be 6V (or 12V if 6V gives too high currents). It will probably be a Li-Ion battery.

My question is: What kind of circuit will I need to charge the Li-ion battery with my solar cells? It would be an advantage if it is as simple/cheap as possible, but still treating my batteries properly.

Thanks in advance.
 

Sceadwian

Banned
There are many dedicated Li-ion/Li-poly battery chargers IC's out there from various makers. I would not recommend home brewing your own, it'll be cheaper to buy a custom made IC for it than do it yourself.
 

halvorlu

New Member
Which IC?

Thanks for your answer. Could you give me a few examples of which IC's i could use? I'm not very experienced when it comes to electronics...
 

Sceadwian

Banned
You can check Digikey or possibly Mouser, I can't recommend any off hand though other users here might be able to. Just look for Li-poly Li-ion charge IC's.
 

halvorlu

New Member
Thanks again. As I see it, I have (at least) three goals:
  1. To operate the solar cells at their maximum power-point
  2. To charge the Li-ion battery properly
  3. To deliver enough power to the loads

I would greatly appreciate a simple schematic or something similar to help me on the way. At the moment I really don't know where to start, and I have quite a few unanswered questions... Can I connect the charger to the battery and then the loads directly to the battery? Can I use a MPPT (maximum power-point tracker) and Li-ion charger IC in series to achieve goals 1 and 2? Where do I find a Li-ion charger IC for such high currents?
 
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