Do you only want the photon to work when it the solar panel is illuminated ?
If not, then you’ll want to use some form of battery shield (SparkFun have one, Particle have one and I believe will be selling it just as soon as they can get their ecommerce site to understand the shipping constraints on LiPo batteries…)
Well… Curious… My current setup involves a SparkFun battery shield, a WeatherShield and the Photon.
What I want is the system to have enough power to charge and be used during the day. I am charging a 2000mah lipo… When it goes dark, I will enter a battery conservation mode… Where the weather instead of being reported every 10 seconds, will be reported every 3 minutes and in between the wifi radio will be turned off to conserve energy.
Also a DEEP sleep mode will be used if the power for some reason goes bellow 30% charge. Then the deep sleep will be waken every 2 hours. After two hours of deep sleep the system will boot, report status and decide if it will keep in low power mode, deep sleep again or return to normal mode depending on the power.
What I want to determine is how big a solar panel I need to charge the battery, use the photon with WiFi and still contemplate a not so sunny day.
Now the take home value, is I want to learn how to calculate this things .
Any help welcomed!
PS @AndyW I tested the other project with the isolation transformer. Works great! I am still alive! On my first trip to US, Il send it back to you!
Do you have a part number for the 10W solar panel!
I bought a 5W from adafruit, if I can’t find a 10W il wire two in parallel.
Is the photon ON 24x7? Or do you use sleep mode or turn off the radios or shut down at night? Or at intervals?
After the solar cell, I am guessing you have 12volt cell… Do you regulate the power to the VIN of the photon or how do you hook it up to the photon. I am guessing VIN input has to be regulated with no more than 5.5Volt?
Its charges OKish, it gets to 85-90% during the day and doesn’t seem to get any higher… i guess its a voltage thing with the tiny solar panel. overnight it was dropping to about 50% and i estimate it was on for about 10min total.
last night i had the unit inside and had it in programming mode (keeps the unit on) and flashed the photon a few times and drained the battery down to 30%. It went back outside at 8am this morning, now at 10.30am its at 63%. The location of the panel is slightly obscured by trees too so its not direct sun the whole day.
Thank you for great information… I guess il use two 5 watt panels in parallel. I will leave the photon on while the power is above 50% when it drops below I will enter intermittent mode… (Radio off) for periods,… If it drops below 20% I will enter deep sleep mode for 4 hours to allow either day charge or to allow night to turn into morning… Il report my findings…
I wish I could calculate all this instead of doing it by heart.
I am still worries that I need to regulate the 6V to 5V… The weather shield has a regulator. I will try to configure it. And use it.
You can calculate with such a method: for simplicity assume your Photon draws 100mA at 5V. It means Photon consumes 0.1A x 5V = 0.5 W. If it runs 24x7 daily consumtion is 0.5W x 24h = 12 Wh. This amount of energy must supply your solar panel. Now look at this map: Solar Insolation Map and locate place where you live (this map shows data for USA. If you live in other country google to find out). Let’s take zone 5 for calculation: daily average (over the course of the year) amount of solar insolation is 4.2 hour. If your solar panel rated 5W means it gives 5W at STC (standard testing conditions). In practice it is only 70% of this value. So you have around 3.5W. Daily you get from solar panel 3.5W x 4.2h = 14.7 Wh. You can see it is enough to power your Photon. Use 10W panel or more if you want more power for some thing else or to secure when no sun light (rain for example).
Hope that it’s useful.
OK so i added some code to track how much awake time my photon has or you,
Awake 683sec 1.05% of total 65000seconds
and this dropped the 2200mAh battery from 85.1% to 75.2% while the solar panel was covered over 18hrs
I change the times slightly too, so that’s based on awake for 15sec, sleep for 30min, unless woken by pulse. And it calculates and publishes 4 strings during each awake time.