pátek 30. ledna 2015

Solar power - part I

A small experiment this evening. This is a standard basic MC34063a step-down converter attached to two solar panels in series. The panels are rated 9V / 5W, but I sincerely doubt they would get anywhere near that. Last time I tried, I got a few milliwats from them on a cloudy winter afternoon... Anyway, my first attempt to use them with my beloved KIS-3R33S converter failed - that thing draws way too much current, making the solar voltage drop to 4V which is too low for the KIS to operate.
That's where MC34063a comes into play. Since I bought a handful of KIS-3R33S modules, I did not use any MC34063a (except for LCD panel driving voltages). It works great, playing nicely with the solar panels even when exposed to a 30W desk lamp, and makes a blue led shine! I've set the output voltage to 4.5V, but I might increase it a bit over 5V later as it will feed a bunch of goldcaps rated for 5.5V.
One thing I quickly realized - I'll need a Schottky diode to make sure the goldcaps won't discharge back through the converter on low light condition.
The plan is to convert the output voltage with a LDO to 3.3V and make my sensor nodes run from it. It's a bit of overkill, but at the moment I have no good use for the solar panels, and letting them just sit in the cellar is a waste. I need to find a good place for those panels, probably on the balcony. That'll be a challenge as my wife fills the space with flowers and stuff every spring. On the other hand, I won't need that much of light after all, and the balcony is mostly empty in winter. I'd guess that the amout of light available to those solar panels will be about the same in summer and winter after all!

On another note - I ordered two GM tubes from Bulgary, one CBM-20, one CBM-20U. The SI-3BG I have made a great proof of concept, but it's not really sensitive, and my best uranium ore sample barely makes it tick. No wonder, the tube is supposed to be used to detect high doses (300R/h). Anyway, the simple GM counter I made works, and with those new tubes... mmm!

Another thing I ordered today was a few thingies from China, namely the BMP180 barometric pressure sensor. I am considering complex sensor node - humidity, barometric pressure, temperature... and radiation background *insert evil grin here*

Žádné komentáře: