I'm working on a project where I want to supply a magnetic valve powered by two parallel connected Li-ion batteries. Each battery has a voltage of 3.7 V (max. 4.2 V) with a capacity of 3.5 A (in total 7 A).

The magnetic valve need 12 VDC to operate and consumes 3.8 W (approx. 320 mA).

I'm using a step up converter to boost the voltage from 3.7 V to 12 V.

My research includes the following points:

  • the magnetic valve isn't working when I only use one battery.
  • the magnetic valve is working fine if I use two batteries in parallel (capacity 7 A, 3.7 V). I assume that the maximum capacity has an impact on the consumer. Why?
  • In my final circuit I use more components than just the magnetic valve (ESP32, 5 V relay, sensors, etc.). If I connect the other consumers the step-up converter is unable to supply the load for the magnetic valve anymore. Before the step up converter I measured 350 mA (which is fine), after the step up converter 100 mA. 100 mA is not enough to supply the magnetic valve and make it work.

Is the range of the step-up converter to boost from 3.7 V to 12 V simply too large to supply 3.8 W (320 mA)?
In different videos I learned that this step up converter should be used from 5 V up.

Is there any way to solve the issue with this step-up converter?

  • 1
    \$\begingroup\$ how about use the two batteries in series to give you the required more than 5 V input? \$\endgroup\$
    – Neil_UK
    Oct 2, 2022 at 19:12
  • \$\begingroup\$ are you certain that the battery capacity is 3.5 A ? \$\endgroup\$
    – jsotola
    Oct 2, 2022 at 19:14
  • \$\begingroup\$ Two batteries in series is working fine but now I need buck converter to reduce the voltage from 7,4 to 5V for other consumers... :/ \$\endgroup\$ Oct 2, 2022 at 20:20
  • \$\begingroup\$ I need to add that I want to charge the batteries by a solar panel. Means, I need an additional charge module. Charge modules operating with 2 batteries (7,4V) are very rare. Stay to 3,7V would be great. \$\endgroup\$ Oct 2, 2022 at 20:38
  • \$\begingroup\$ I realized that there is no way around using 7.4V to supply the magnetic valve. I ordered all parts needed to make it work. Thanks for your input! \$\endgroup\$ Oct 3, 2022 at 22:31

2 Answers 2


In different videos I learned that this step-up converter should be used from 5V and above.

Yes. "Optimal operating voltage range: 5 V to 30 V"

Something like this could be better, from 2V ...
Made with MT3608.

  • \$\begingroup\$ I tried the MT3608 but it's not working. I can even hear an unhealthy beeping. ^^ \$\endgroup\$ Oct 2, 2022 at 20:22
  • \$\begingroup\$ Ok. Will check it. \$\endgroup\$
    – Antonio51
    Oct 3, 2022 at 5:44

I have a solution for you. Because I used it on 2019.enter image description here

enter image description here

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    Sep 26 at 3:25

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