I'm going to be building a solar powered Li-Ion battery charger for a class project, and I just wanted to ask a few questions that I hope some of you may be able to help me out with.
First off, here are the specs for the battery: Camera: Minolta DiIMAGE G500 Battery: Lithium Ion NP-500, 3.7V, 820 mAh
I think I found a good match for a solar cell and IC - the links are below:
Unfortunately the only specs given for the solar cell are Voc = 8V, Isc = 310 mA. I also estimated the power dissipated in the IC (as per the equation in the datasheet) and it is nearly negligible - about 50 mW.
Some assumptions that can be made are the device will be used only during peak sun hours and will be angled perpendicular to the sun for maximum insolation on the cell. I don't necessarily need the battery to fully charge in one shot, but merely keep the battery from dying over the course of a week or so.
So with that said, is there a way to determine (or estimate) the operating point of the solar cell without an IV curve? Obviously the output of the chip will be around 4V (battery voltage), so does that imply the solar cell will be operating at that voltage? The pulse charger requires a current limited source (which a solar cell is inherently), so will that mean the solar cell operating point will be the lowest Vcc at which the IC will operate, in order to maintain the highest current? I'm just confused as to how determine the operating point of a device that uses a pulsed current, where the high current value is basically the maximum the solar cell can provide.
I'd also like to do a load analysis. What do you think would be the best way to do this? I know most are simply a static voltage and current value multiplied to give you the power (and also time the device will be used to yield an energy figure). Again, though, the IC is a pulse charger and has two main sections in the charge cycle - constant current and constant voltage (where the current pulses decrease until it reaches full charge). Should the load analysis follow the complexity of the device, or would a simple estimate of output voltage and charging current suffice?
Please do not reply with comments such as 'this project is pointless, just use a car battery adapter for power', or 'you can buy a solar powered charger at this website'. I'm doing this project and want some helpful input! Any suggestions or help in understanding the solar cell operation with this chip and battery are greatly appreciated! Thanks so much.