Solar-Powered Espruino + CC3000

Posted on
  • I try to power the espruino incl. a CC3000 WiFi module via a solar panel - the panel is charging a 12V battery and the 12V battery is connected to VBAT and GND of the espruino.

    Now, the CC3000 was connected to VBAT, but I assume 12V would kill it. So I use the 3.3V pin on the espruino to connect the 3.3V pin on the adafruit CC3000 breakout.

    It does not seem to work - maybe the CC3000 does not have enough power. But I think 5V is max for the CC3000. How would I connect the Espruino to 12V, but still supply enough power to the CC3000 - is VBAT with 12V an option?

  • OK, although I've been super careful and really never connected BAT (which was 12V during the time the solar panel was connected), it seems my CC3000 is burnt. I've had troubles connecting and finally switched the CC3000 against a second one that I have. In the old setup, with 5V connected to the micro USB, CC3000 again on BAT/GND, it now works again.

    During the solar panel testing, I really unplugged espruino from power, then connected CC3000 to GND and 3.3V - as BAT would now be 12V - and started up. After that did not want towork, I began investigating.

    Is 3.3V on Espruino guaranteed to be 3.3 - even if a 12V battery is connected to BAT and GND?

  • the 3.3V regulator is very tiny, and I would not connect a 12V battery and expect it to work. a look at the datasheet for the MIC5205 shows that the temperature rise is about 220 degrees per Watt. if the Espruino draws 35mA and we connect a battery with 15V then the dissipation is 0.41W which means that we may reach over temperature and the regulator shuts down. it is better to use a 5V USB charger of the type you plug into the cigarette lighter in your car, between your battery and the Espruino. this way you can add some additional load to the 3.3V (about 100mA I believe). or you can power your extra gadgets from 5V.
    be aware of the danger when you connect a battery. the battery voltage can be above 15V and there is an inrush current at plug in because the capacitor at the input of the 3.3V regulator is quickly charged. there can be an overshoot in capacitor voltage because of the inductance in the battery leads (an LC resonant circuit is formed) and if the resistances are low, the capacitor voltage can theoretically double when you plug in the battery. this would kill the regulator.
    if you are working with solar panel charging of the battery you should also be aware that the voltage from the panel will be as high as 24V when the battery is not present.

  • Also, the Espruino's 3.3v is rated at 150ma, but the CC3000 peak current is 350ma - there's no way it's gonna work off the Espruino's internal 3.3v.

    Note also that the CC3000 board VCC spec is 4.6 max - this means you can't expose it to 5v, though the 4.3 off USB is okay).

    I think you're going to need a dc-dc converter of some sort - the 12v->5v stepdown ones for USB car chargers (also available as bare boards from china - dirt cheap either way) might be a good choice.

    I would be inclined to use a 1S LiPo battery or a 18650 cell, and charge it with an appropriate charging board (powered off a 5v dc-dc converter), instead of using a 12v battery, though this might not be appropriate for your application...

  • Espruino's voltage regulator is only 150mA so it won't power the CC3000 - unfortunately bigger regulators draw way too much power.

    The Adafruit module has a very hefty 3.3v regulator on-board though, so it should run off of a 12v battery just fine unless I'm mistaken... See the schematic:­assets/000/010/985/original/adafruit_pro­ducts_cc.png?1379351147

  • Woah, so that means I could connect the CC3000 to BAT and the espruino itself is also powered via the battery, which is 12V. As I got just one CC3000 left, I'll not try it out now but it's great to know.

    Just wondering: when the other CC3000 died, I really connected it to a 3.3V pin of espruino (and 3.3V pin on the CC3000) and the GND of course. Other pins are unchanged. Now, it might have just died as it was time for it to die, but would there be another reason I am just too blind to see? I would have expected the espruino to die if the max power I can get across all 3.3V pins is 150mA - wouldn't that somehow overheat the espruino, but not the CC3000?

  • Yes, it's strange. You'd have though that the voltage regulator on the Espruino (the small black IC by the JST battery connector) would have got quite hot and maybe died - but otherwise I don't know what killed it - unless you accidentally connected it to 5V by mistake one time?

  • Post a reply
    • Bold
    • Italics
    • Link
    • Image
    • List
    • Quote
    • code
    • Preview

Solar-Powered Espruino + CC3000

Posted by Avatar for hansamann @hansamann