Electronics > Power/Renewable Energy/EV's

100W 12V to 4.2V buck converter / voltage regulator ?

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ponas:
Hi there,

 So I want to run a small, purely solar powered, linux "server" based on Olimex A64-OLinuXino-2Ge8G-IND.
Olimex board has a battery connector (JST) which can be used to power the board, as well as getting battery voltage, discharge rate, etc all from within the linux running on the board (no external voltage/current sensors required, which simplifies whole setup).

For the solar panel I've chosen 100W SPR-E-FLEX-100.

Now the battery. Olimex battery connector supports single 18650 or multiple connected in parallel, so I plan to make a 20P (or so) battery pack (and use protected cells!).

The challenge I have is how to charge the battery pack as fast as possible, because solar panel location will be suboptimal. So basically I'm looking for a 12V to 4.2V buck converter, which can handle 100W or so.

I found couple of cheapish Chinese buck converters ala.

https://www.prodctodc.com/10a-dc-buck-converter-10v35v-to-42v-stepdown-power-supply-volt-regulator-p-375.html

but I'm not sure if I can trust them running 24x7 all year around, so I'm looking for a high quality and efficient alternative.  Best, of course, would be a solar charge controller which would output 4.2V, but I have not seen such controllers as they usually support 12V or 24V batteries only... Any ideas ?

fourtytwo42:

--- Quote from: ponas on March 28, 2019, 12:14:04 pm ---I found couple of cheapish Chinese buck converters ala.

https://www.prodctodc.com/10a-dc-buck-converter-10v35v-to-42v-stepdown-power-supply-volt-regulator-p-375.html

but I'm not sure if I can trust them running 24x7 all year around, so I'm looking for a high quality and efficient alternative.  Best, of course, would be a solar charge controller which would output 4.2V, but I have not seen such controllers as they usually support 12V or 24V batteries only... Any ideas ?

--- End quote ---

Hoverboards come to mind (the exploding catching fire variety)! I don't think Lithium chargers are as simple as that.

george80:

If you are using 18670's you will need a proper charger.
They are cheap as chips on ebay. you would be very unwise just to hook them to a power supply especially one that does 4.2V which is right at their upper, life shortening limit.

Just look through Ebay, aliexpress, bangood... whatever.
 Hardly a rare thing to get.

NiHaoMike:
Connecting all the cells in parallel avoids the usual balancing problem, at the cost of high currents. You'll be looking at up to 30A or so, enough to make the converter design still fairly easy but not trivial. Limit the voltage to 4.1V/cell or less and the charge current to 1C or less for good service life.

100W of solar sounds like a lot to run just one single board computer - I have personally used a single 100W panel to power 4 cheap smartphones, 2 old tablets, two Raspberry Pi 3s, and a small mining ASIC with some power left over. (All of those were part of my cryptocurrency mining setup, the Raspberry Pis used as management controllers and the rest calculating hashes.) I used a 4S LiFePO4 pack (12.8V, 82Ah) with a balancing BMS, then used buck converters to step that down to 5V to actually run all the equipment.

Seekonk:
Running a solar panel into a buck converter can put it into a death spiral reducing maximum power.  The panel can be kept at power point  with a simple circuit that fakes the feedback pin of the converter into thinking there is an over voltage on the output.

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