Want to power a GPS with solar, need help!

[Grandpapabi]

Hi, I would like to power my Garmin ETREX VISTA with a solar array. I know that The GPS as a current draw of 90ma to 130ma depending on which mode I am. I bought 10x 3v 25ma solar cells, the GPS needs at least 2.75 volts to work, and a maximum of 3.3v. I did a bit of reseach, and i've been mesuring the voltage i'm getting a various sun exposure with no load. I would like to be able to use the GPS an a fairly cloudy day. So far i'm getting around 1v at the worst condition i'm willing to use the GPS. So, in order to regulate the power to the GPS regardless of the exposure to the sun, I think I need a voltage regulator " a 78L03" that as an output of 3v 200ma and the input voltage could be as high as 20v. So far i think i'm in the right ball park, I yust want to know at which voltage should I feed my 78L03 (which I think need a differential of 3v to work properly) and how much current should I supply? If you need more info on the parts or ETREX let me know I'll try to dig them out. Your help would be greatly appreciated.

Thanks to all!

 

[Grandpapabi]

Please help.

 

[Russlk]

The LF30AB voltage regulator (ST Microelectronics) will do a better job. The needed differential is less than 1 volt and current limit and power limit are built in. You need to supply the maximum load current (130mA) and voltage of 4 volts minimum, 40 volts maximum.

 

[Grandpapabi]

Great, thank you Russlk for your replay, it's really appreciated. I'll get to work with this info. Do I need capacitor between the leads like the other circuit I was mentionning?

 

[Russlk]

You will need input and output capacitors for stability, read the data sheet, which is available at www.mouser.com.

 

[Grandpapabi]

Hi, I made a schematic of the circuit. Just le me know if it's what I should do. I'm pretty sure i'm right with this. Please let me know if I did it right.

Thanks

 

[Russlk]

That looks good to me.

 

[Grandpapabi]

Thanks, your help has been really helpfull!

 

[Grandpapabi]

Hi, I've made my little curcuit and something must be wrong? I'm not getting my 3v output like I was supposed to. If you look at the pics, you will see that i'm not even getting 0.6v. I think i've connected everything the right way, according to my schematic. Can you think of something wrong with this? I've observed the polarity for the 2 capacitors, long leg positive and short negative. Could it be my ground that's not right, or maybe my iron for soldering burnt my IC? On my panels I was getting 6 7 volts and nothing good on the other end. i don't really know what to do next?

 

[Grandpapabi]

Some one review my connections please!

 

[hjames]

The connections look fine, remove the solar cells temporarily and plug in a 9V battery to double check things...

James

 

[Grandpapabi]

Good idea, i'll check that! Thanks

 

[Grandpapabi]

YEAH! I've solved my problem, I had a wrong connection. It's working ok now, exept that 125ma seems to be a bit short. So i'll upgrade to 9v 175ma. That should help on the "enough sun" and the current available. Thanks everyone for your help!

 

[hjames]

YEAH! I've solved my problem, I had a wrong connection. It's working ok now, exept that 125ma seems to be a bit short. So i'll upgrade to 9v 175ma. That should help on the "enough sun" and the current available. Thanks everyone for your help!

Solder problem? Putting 9V worth of solar cells across it definitely isn't required - unless you're going to be working in some pretty dark conditions. I'd suggest that you just parallel more cells together.

 

[Grandpapabi]

OK, you are right, except that the voltage drops pretty fast when the sun is not shining. And I'll probably use this device more on a cloudy day then on a bright and sunny day. For now I only get around 1v per cell for a cloudy day, so I don't get my 4 volts minimum. Anyway, I'll make some tests and I'll se what's better, more amps, or more voltage. Thanks again everyone for your help.