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2018/06/30 DC charging with DC to DC conversions when off the grid
π 2018-06-30 01:01 in Bm, Electronics
When you're off the grid (for many, still true at burning man, or Ephemerisle, you can:
  • bring big batteries (Li-Ion USB packs and/or big Lead Acid Batteries (AGM is better than car battery)
  • use solar panels to help recharge the batteries, but most people don't quite realize that panels need to be sufficiently big (and heavy) to charge sufficiently. You also need a charge controller.
  • use a generator. Generators are quite efficient and cheap for occasional use and make way more power than solar panels per unit of weight. Sadly, they are noisy and not environmentally friendly.
  • The ideal solution is batteries only if your event isn't too long and you've done the math that the batteries have enough Wh for your needs
    Next, is usually batteries + generator that you start as needed. Solar is really the best solution, but it requires more complicated hardware and setup (charge controller, MPPT charger, etc...), but more importantly for any non trivial power need you actually need pretty bulky and heavy panels to handle the load (of course this also relies on you being able to count on enough sun during your event at that location, not an issue for burning man, but potentially an issue for a spring festival in some place that could be overcast or maybe even rainy).

    12V Charging

    Anyway, back to charging, your best bet is to use 12V lead acid (marine, or AGM are even better), and use DC to DC converters to power all your stuff. For 12V, well, you're done, just plug into that using the appropriate cabling with fuses. You will likely be happy with those two:
  • DC 1 Female to 8 Male Power Splitter Cable for CCTV:

  • SoulBay 34pcs Universal Laptop Notebook Input DC Plug Set Jack Tips for Lenovo Toshiba Dell HP Asus and most Laptops: (sadly even some simlar looking barrel connector are not actually the same)

  • Plenty of chargers work off 12V, you may just need to use some barrel adapters:

  • Socket Cigarette Lighter Power Adapter DC Outlet Splitter + 2-Port USB Car Charger:
  • small 12V lipo charger for 1S to 4S lipo: (cheap but slow)
  • AccuPower IQ338 Fast Charger and Analyzer Tester: Li-Ion + C/AA/AAA battery charger (fast)
  • XTAR Xtar-VC4-Charger-T VC4 Li-ion/Ni-MH Battery Charger Premium USB: Li-Ion + AA/AAA battery charger (slow)
  • Powerex MH-C9000 WizardOne Charger-Analyzer for 4 AA or AAA NiMH Batteries:
  • 20V and other higher voltage high amp charging

    Now, some laptops may charge from 5V USB if you're lucky (but that will be slow). Some will charge from USB-C which may allow 12V charging or even 20V charging, but finding such a charger that works from 12V may not be trivial. In the case of my thinkpad, it just plain requires 20V, and not only that, it requires 20V at 5.5A or it will power itself, but it not charge (yes, it is stupid).
    I wrote this page on how to hack a 20V power connection to look like it's at least 135W so that a thinkpad will charge, however I need to upconvert 12V up to 20V with more than 10A from the 12V source. I used a discontinued version of this boost converter, and I also have a 100Wh Li-Ion battery pack that can output enough power to sustain my laptop, but not to charge it. That one also requires 20V to charge (sadly it won't charge from 12V):
  • 16A DC Boost Voltage Converter 12-60V to 12-80V Step-up Power Supply Transformer Module Regulator:
  • RAVPower 100Wh USB battery pack, 20V charging, 9 to 20V output for laptops (plus USB):
  • this battery pack can output 9, 12, 16, 19, or 20V
    this battery pack can output 9, 12, 16, 19, or 20V

    You can see the 12V being split and going into the little white box with the step up boost converter. It shows that it's taking 3.5A at 12V and the red display next to the laptop shows it's turned into 1.7A at 20V which goes both into the already charged laptop and the almost charged ravpower battery pack:

    it might not look like much, but this is my new 160W laptop power supply :)
    it might not look like much, but this is my new 160W laptop power supply :)

    5V USB charging

    Now, let's look into 5V charging, i.e. USB devices. There are plenty of ways of turning 12V into 5V, that's what all car phone chargers do, but most don't deliver many amps, and don't allow full speed charging for more than 2 or 3 devices on a good day. As a result, I'l recommend this 14 port anker USB hub where you'll ignore the USB part and simply use the fact that it has 80W of charging capacity from 12V input:
  • USB Power Hub that will provide 14 outlets at 1A each (works off 12V power):
  • you can see the anker 14 port USB hub next to the powerex battery charger for scale
    you can see the anker 14 port USB hub next to the powerex battery charger for scale

    Then, I personally use this for my trips when I want a lot of USB (5V) power:

  • RAVPower Battery Packs 26800mAh Total 5.5A: (can charge and discharge at the same time)
  • USB C RAVPower 26800mAh: with USB-C support at higher voltage for fast charging:
  • And here is the end result, lots of different chargers all from that same 12V source (including all the adapter tips in the upper left)

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