Solar Freaks

Hi, great forum.

So I am using a Linear Technologies LT3652(data sheet) Peak Power Tracking solar charger IC for a project.

From the data sheet, "Connecting a resistor divider from VIN to the VIN_REG pin enables programming of minimum input supply voltage, typically used to program the peak power voltage for a solar panel."

So my question is, how do I calculate the peak power voltage for my particular panels? I am using some 6v 400ma panels that I eventually hope to use to charge a pair of Li-ion batteries.

Googling suggests that I use some power wirewound resistors and plot the voltage vs calculated current. Is there a better more efficient way?

Any help will be greatly appreciated!

Hi DisplacedTexan,

Typically, you will need a variable load, and a power meter, but personally i think its not worth going through that.

All i would do is, measure Voc at full sun and NOCT. Then take a value of 0.75 x (Voc) as your Panel operating point. You will see that for any solar panel of reasonable quality, the maximum power point is usually at 75-80% of Vin.

So if you have a 10V panel, take 7.5V as your working voltage.

TonyB,

Thanks for the quick response. It's amazing how someone who knows what he is doing can answer a question that days of me googling couldn't.

Another quick one... from page 16 of the data sheet:

Code: Select all

The LT3652 contains a voltage monitor pin that enables programming a minimum operational voltage. Connecting a resistor divider from VIN to the VIN_REG pin enables programming of minimum input supply voltage, typically used to program the peak power voltage for a solar panel. Maximum charge current is reduced when the VIN_REG pin is below the regulation threshold of 2.7V. If an input supply cannot provide enough power to satisfy the requirements of an LT3652 charger, the supply voltage will collapse. A minimum operating supply voltage can thus be programmed by monitoring the supply through a resistor divider, such that the desired minimum voltage corresponds to 2.7V at the VIN_REG pin. The LT3652 servos the maximum output charge current to maintain the voltage on VIN_REG at or above 2.7V.

So, do I want to set (via voltage divider) VIN_REG to the peak power voltage? If I reading the above correct, VIN_REG is used to program a minimum input supply voltage. Do I want to set the minimum voltage to the peak power voltage? Common sense says I don't...

If not, generally what minimum voltage value do I want for solar panels with Voc of about 6.5-6.8v.

Thanks again...

Hello DisplacedTexan,

I'm discovering the LTC6352 component and i'm very interested by its capacitys.
Do you succeed in the configuration of the regulation of the photovoltaique pannel?
Which type of batteries do you use?

Thank you very much for your informations.

Christian

I to have been looking with interest at this chip - just trying to fathom how to solder that *TINY* package!

I have been lucky enough to get some "pre-production" versions in a bigger package but they are still TINY!!!

Have you had any luck with your project? I'm trying to use them to make a more efficient solar regulator for small telemetry systems (panel size max 20w) so that we can do way with the bulky commercial regulators we have to use at the moment

Regards

Stocky