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misch2 / ups12v

12V UPS
MIT License
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Ideas for V3 #1

Open misch2 opened 4 months ago

misch2 commented 4 months ago

Because the V1 works but for small currents only and the V2 failed, I'm considering a new approach:

  1. Use 4S 18650 to achieve 12.8 - 16.8 V which could then be connected to a much more efficient buck (step down) converter
  2. Power the whole thing from 19 V or 24 V source, eliminating a need for boost converter charger
  3. Use CC/CV capable buck DC-DC converter + BMS to charge the battries. The converter will take care of charging, BMS will protect the batteries.
    1. Maybe add a disconnection circuit (or EN pin on the converter) to allow for a software defined charging stop.
  4. Use 2nd buck converter on the output to produce 12 V (with >= 3A) from batteries
  5. Use P-type MOSFET to control batteries output (to prevent continuous load sharing)
  6. Optionally generate additional output voltages if needed (9V or 5V etc.), always with it's own additional buck converter.

This would also produce smaller currents compatible with INA219 and with narrower PCB traces.

Rough idea: image

misch2 commented 4 months ago

For example this step down https://www.laskakit.cz/step-down-menic-s-xl4016e1/ should handle up to 8A and convert 24V to anything between 2V - 22V.

Alwo with 24V / 16.8 V / 12V combo there's no need for a MOSFET to prevent load sharing: when powered the D2 diode has always 24V and is therefore reverse-biased. Only when the input power drops below the battery voltage the D2 will get foward-biased and will start to conduct.

Controls

RELAY1: test or calibrate the UPS (force disconnect the input)

RELAY2: disconect the output. This might be a bad idea, possibly do not even use it.

Q4: disconnect the CC/CV buck converter. And as D2 is normally reverse-biased the batteries should last long because they won't be permanently being charged or discharged. MOSFET is better than relay here because it's going to turn on and off quite often and a realy might be noisy.

misch2 commented 4 months ago

Updated schematic: image It's still missing a lot of circuitry (ESP32, relay drivers, current/voltage sensors etc.) but in principle it should work. Time to test it.

misch2 commented 4 months ago

⚠️ Don't forget that IRF5210 (and almost any other MOSFET) has |Vgs(max)| < 20V.

Simulation for controlling the IRF5210 using 3.3V source:

image

image

This should be within a safe Vgs range. For 3V3 on input it produces -12V as Vgs.

⚠️ CC/CV buck converter has a separate GND on IN vs OUT. There's a shunt resistor between them and it must not be clamped otherwise the CC won't work. Separate GND1 and GND2 must be used there!

misch2 commented 4 months ago

Good point on CCCV modules with isolated ground: https://forum.arduino.cc/t/using-constant-current-buck-converter-with-common-ground/861109/4