Searching for a suitable Solar powered Li-ion charger

[Doedakse]

Hi all,

I´m currently designing a PCB with a solar powered Li-ion charger on board.
After a lot of searching and reading I still can’t make a good choice for a suitable (solar)charger.

My target/requirements are:
- Retrieve the highest efficiency possible from the solar cell and battery charger. 
- (Aim to) fully charge a 2200-3500mAh Li-ion battery on a daily base. (Outside, on a cloudy day and in shadow too). 
- During charging the load (<10mA) is active.
- The maximum dimenstions of the solar cell(s) are 15x15cm, but I prefer smaller ones (e.g. 5x10cm and place them in series). 

I hesitate between several IC’s/solutions:
- BQ24210 (TI)
- SPV1040 + L6924 (ST)
- MCP73871 (Microchip) (not explicit for solar charging, but I have seen some projects which used this IC).
- LT3652

All these solutions have their pro’s and con’s. Does anyone have experience with one of these solutions?
If yes, what are your thoughts about these solutions?
Would you recommend one of these or do you have another (better) solution?

A step in a right direction would be awesome! I would appreciate your help very much!


Kind regards,

Martijn

[ahbushnell]

Hi all,

I´m currently designing a PCB with a solar powered Li-ion charger on board.
After a lot of searching and reading I still can’t make a good choice for a suitable (solar)charger.

My target/requirements are:
- Retrieve the highest efficiency possible from the solar cell and battery charger. 
- (Aim to) fully charge a 2200-3500mAh Li-ion battery on a daily base. (Outside, on a cloudy day and in shadow too). 
- During charging the load (<10mA) is active.
- The maximum dimenstions of the solar cell(s) are 15x15cm, but I prefer smaller ones (e.g. 5x10cm and place them in series). 

I hesitate between several IC’s/solutions:
- BQ24210 (TI)
- SPV1040 + L6924 (ST)
- MCP73871 (Microchip) (not explicit for solar charging, but I have seen some projects which used this IC).
- LT3652

All these solutions have their pro’s and con’s. Does anyone have experience with one of these solutions?
If yes, what are your thoughts about these solutions?
Would you recommend one of these or do you have another (better) solution?

A step in a right direction would be awesome! I would appreciate your help very much!


Kind regards,

Martijn

You don't say what the battery voltage is?  Do you have more than one cell in series?
How much power do you expect to use?  15x15cm is 2.25e-4 m^2.  In Arizona (i.e.) desert the sun produces about 1 kW/m^2.  If the cells are 15% efficient that's about 34 mW.  If your load is 10 mA on a 3.5 volt cell that's 35 mW.  I assume you want to use the load 24 hours per day?  You will need 35 mW*24 hours=840 mW-hr.  If the the solar cells produce34 mW* 6 hrs=204 mW-hr.  Now your going to want to do this on a cloudy.  That will reduce the power a bunch. 

And I assume your not in Arizona. 

Good luck.

[Doedakse]

Hi Ahbushnell,

Thank you for your reply.
The battery voltage is 3.7V (1S1P).
I expect to use between the 8W - 10W of power namely during the nights.

The calculation is not really the problem, i'm confused of the many solutions on the market to harvest solar energy.
Perhaps you got a recommendation of a solution I've mentioned in my earlier post, or another solution?


Kind regards,

Martijn

[janekm]

If you do want to extract usable energy during partially overcast (forget about heavy cloud cover) then a perturb&observe algorithm such as implemented in the SPV1040 is going to be helpful. The other chips all appear to assume that the maximum power point is at a fixed voltage which is not the case with varying insolation.

[Doedakse]

Hi Janekm,

Thank you for your reply.

The SPV1040 has a bit my preference, the only thing is that the SPV1040 is not able to proper charge a Li-ion battery.
So what if I use the following setup:

SOLARCELL -> SPV1040 -> MCP73871* -> LI-ION
*Could be replaced by a different charger

Would this be a good idea? Or is this overkill?


Kind regards,


Martijn