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I'm designing small 5 volts UPS that would allow me to run on battery or 5V source.

If source is unavailable, step-up module takes power from battery.
If this 5V source is restored, then this source is taken for step-up module, but also battery is being charged

There are two diodes, so only one source will be taken to step-up module, by comparing voltages - 5V or from battery (3.7-4.2V),

I've decided to do it semi-DYI, so I used some ready made components,
but I'd like You to review these connections.

Connection and modules in short:

  • charger module is a widely available TP4056 module, available for few bucks. It stops charging at 4.22V and resumes charging when battery voltage below 2.8V
  • Li-ion battery is a 18650, 3.7V one, scrapped from battery bank (no protection)
  • two diodes shown on image below are Schottky 1N5819 1A / 40V
  • at the output, I have step-up module that gives me a stable 5V/500mA source for devices connected

Is this module safe to leave it unattended, or maybe you would change something here, like adding extra protection, modules replacement ? I used Schottky diodes, but since this is my first real electronic project (without the ones did for a fun and learn), I didn't want to complicate this design with PNP/NPN transistors. I need to know them more, or learn all theirs weaknesses first.

enter image description here

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  • \$\begingroup\$ It appears that your diagram is not showing the "correct" connection between the battery (+), the charger output (+), and the diode connected to the battery. They should be the same node. this may cause the battery to overcharge/overheat. Also, I would connect the battery to the chip rather than the step up module. \$\endgroup\$ – Guill Apr 21 '16 at 22:06
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The TP4056 module is good for charging but it's quite possible the step up module has a 20mAh or so quiescent current and it might drain the battery even when it's not powering something. If you're not using this for a very low power device then it might not matter.

In my opinion, a better option would be to use something based on TPS61090 such as the PowerBoost board.

Otherwise your concept it's clearly cheaper if that is more important here.

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  • \$\begingroup\$ good catch. I think I'll insert some relay module between 5V and charger. You mentioned TPS61090, but I forgot to mention that my goal is to make something DIY, but still keeping it cheap and safe. \$\endgroup\$ – Alan Staney May 30 '16 at 12:47

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