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Building a rudimentary battery backup for your USB powered devices (IoT, Raspberry, etc)

Posted by jpluimers on 2020/07/14

Malcolm Lewis [WayBack] came with these interesting pastes for a rudimentary battery backup servicing USB powered devices:

Since both expired, here is some more elaboration with Amazon.com links:

From the picture linked above (full one at the bottom of the post): a switch is missing from the parts list (:

Note that this is only the hardware parts, and no measurements of the voltage from the Raspberry Pi. So it is a battery backup, not a UPS.

For a UPS kind of functionality, you need more hardware (measure voltage to assess when to safely shut down, reset circuitry for when power comes up), and software (so the devices can shutdown).

Connections

After IRC chatting with Lewis (see his [WayBack] profile), this is how they should be connected:

  1. USB charger:
    1. OUT connector type A of USB charger cable
  2. Connections to the TP4056 battery charger (a nice video on this is at Charging a Lithium 18650 Cell using the TP4056)
    1. IN mini/micro USB from connector type B of USB charger cable
    2. BAT pins B+ and B- to the + and – of the 18650 battery holder
    3. OUT pins +/- to your LM2577 IN pins+/-
  3. 18650 battery holder
    1. IN pins +/- to the TP4056 BAT pins +/-
    2. One or two 18650 batteries
    3. Note
    4. Most of the wired “parallel” 18650 dual battery holders on non-USA Amazon sites are in fact serial (you see that in the comments, or by watching the wiring carefully), so better buy an unwired one!
  4. Connections to the adjustable LM2577 step-up converter having a max current of 3A
    (get one *with* voltage meter, as voltage meteres themselves are about half the price of the LM2577!)

    1. IN pins from the TP4056 OUT pins
    2. Adjust to slightly above 5V before connecting anything else!
    3. OUT pins +/- to the red/black pins of a connector A stripped micro USB cable
  5. USB powered device (like Raspberry Pi)
    1. Micro USB connector: connector B of the USB cable coming out of LM2577

If you want to measure both voltage and current, then a combined piece like Voltmeter Amperemeter Dual Digital Volt Amp Meter Messgerät 100V 10A is very convenient. Most of these do not come with schematics, so here is one:

Specs

Parts from Amazon.de

Media

There is a 6A module; though I’m not sure it is based on LM2577

Bad battery box example

–jeroen

 

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