I've tried searching through existing topics but haven't found an answer. I'm a beginner enthusiast. I have a couple of questions that I would appreciate input for. My plan is to make a battery pack that can be charged via wall adapter/PC/solar. I have found information here that helped greatly.

1) I plan to use 2x 18650 batteries in parallel as the power supply. The only ones I can find are rated at either 35A or 40A. All others I have found do not list the amp value.

2) Through other questions/answers I have been made aware of voltage boost modules. My concern is that the ones I have been able to find specify a max input of 4A from the battery source. Will the batteries I mentioned above fry the circuit? Will I need to make a step down circuit between the batteries and the voltage boost module to decrease the amps or an I just overthinking this?

3) The modules I found have mini USB connectors for charging the batteries. Can I tap this circuit with a solar panel (with inline diode) to charge the pack instead of a wall adapter or PC? Will I still be able to use a wall adapter if I do this? What is the lowest maH value that would provide a reasonable recharge time? I realize the charge time would increase due to how many batteries are used.

Thank you for taking the time to read this.

  • \$\begingroup\$ What 18650 cells have you found that are rated for 30 or 40A discharge? They're usually somewhere in the 3A to 10A range. \$\endgroup\$ May 13 '16 at 10:19
  • \$\begingroup\$ "18650 battery" is like saying "Toyota car." There are at least two dozen different types of 18650 cell, and depending on the type today, charging certain types incorrectly can lead to fire, even explosion. Which chemistry of 18650 cell are you using? \$\endgroup\$
    – rdtsc
    May 13 '16 at 11:54
  • \$\begingroup\$ The ones I currently have are AWT (brand) IMR 18650 3.7V 3000maH 40A. If you have a type you would recommend for the purpose I stated above, I'm open to input. \$\endgroup\$
    – Kantanshi
    May 13 '16 at 22:27

1) 35 A is a bogus rating for 18650 batteries. This is a "pulse rating", which in practice does not tell you anything of interest. If you buy "high discharge" batteries from a respected brand, they can deliver 20 A or even slightly more of continuous current, but the real continuous rating of the cheap knockoff batteries (and the many counterfeits out there) is anyone's guess. Don't trust the sales pitch.

However, for your scenario this is not a problem, because:

2) The batteries will not output more current than is drawn from them. If your boost module draws 4 A, then that is what the batteries will deliver.

3) As long as your solar panels don't exceed 5 V on the output, feeding the output into a USB socket should work.

  • \$\begingroup\$ So a higher maH current rating for the solar panel is best as long as it does not exceed 5V output? \$\endgroup\$
    – Kantanshi
    May 13 '16 at 22:31

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