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I am using SIM800L which requires voltage range between 3.4-4.7 V with 2 Amperes. On the other hand Arduino Uno requires 7-12 V. The question is how to power both of them with the same Lithium battery?

I have two Lithium batteries each of them is 3.7 V.

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  • \$\begingroup\$ I assume you mean "2 amps" not "2 amber". It is normal to say "between 3.4V and 4.7V at 2A", as current isn't in addiion to voltage. What have you looked at so far? What is the votlage range of your batteries? Areyou plannign on them being series or parallel? What do you have for a battery BMS? You just need two DCDCs, one to give you something between 3.4 and 4.7 volts, at 2 amps, and another to give you something between 7 and 12V at whatever current that Arduino uses. \$\endgroup\$
    – Puffafish
    Commented Dec 16, 2022 at 12:12
  • \$\begingroup\$ I have the batteries in series. They are Lithium Ion batteries 18650 And for charging I have TP4056 board but not really sure how to integrate it in this circuit as it can only charge one battery at a time \$\endgroup\$ Commented Dec 16, 2022 at 13:20
  • \$\begingroup\$ Consider powering the Uno directly from the same source, bypassing its internal (5V) regulator. You may need to make other adjustments (check the requirements of all peripherals you're using). \$\endgroup\$ Commented Dec 20, 2022 at 6:39

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To clarify your question, you want to power two sub-modules. One takes 3.7-4.7V and requires 2A peak. The other takes 7-12V and requires some unspecified current. To power this, you have two lithium cells, I assume lithium ion, and have a working voltage range of between 3.1-4.2V (this is a guess, but will do for now).

You have two options:

  1. Put the batteries in series (ideally with a good BMS for cell balancing, charge control and safety features). This gives you 6.2-8.4V. You then fit one buck DCDC converter to get you something close to 4V (anything between 3.7-4.7V is ok) and can supply 2A. Then you get another DCDC, a boost one this time, which outputs something like 10V, (while you need 7-12V, many boost DCDC don’t handle outputting a lower voltage than the input, so I’m sticking with some good headroom over the max 8.4V the battery may be outputting).
  2. Put the batteries in parallel (ideally with a good BMS for charge control and safety features). This gives you 3.1-4.2V. You then fit one Boost DCDC converter to get you something close to 4.5V (as before, while you need 3.7-4.7V, many boost DCDC don’t handle outputting a lower voltage than the input) and can supply 2A. Then you get another boost DCDC, which outputs something close to 10V, (anything in the range 7-12V will do).

Other things to note, I've asssumed the batteries will be removed for charging. If not, then the votlages used may need to be tweaked as the charger will increase the upper votlage input.

I’d personally go for the first option, as boosting up can be a bit more tricky than bucking the voltage down.

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