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I would like to protect my robot from reverse voltage which is powered by four 18650 cells. Is option 1 sufficient or do I need at least three diodes? I know that using diodes comes with a voltage drop of ~0.6V per diode, but as I use step down modules anyways, that wouldn't really matter in my case. Or are there easier options available? I want to use as few components as possible, preferably common ones I have laying around at home (like diodes, resistors, transistors etc.).

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It depends on which fault you want to protect and what you want to protect. I would say option 1 is probably good enough for what you have in mind.

Option 2 is not a good solution no matter what since you essentially have 4 diodes in series. The drop will be significant and won't protect you any more then solution 1.

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  • \$\begingroup\$ Thanks for your answer, I was not sure whether option 1 offers equal protection. So if I accidentally put in battery 3 the wrong way around, there would be no current flow through the battery? \$\endgroup\$
    – Michael Brown
    Commented Aug 17, 2023 at 17:23
  • \$\begingroup\$ If you have 1 cell reversed (assuming VCell=3V) of the 4, you would have 6V instead of 12.V. The current will be reversed in that cell, but the diode will allow it (unless the diode is inside your battery, then it would block everything) \$\endgroup\$
    – Julien
    Commented Aug 17, 2023 at 17:42
  • \$\begingroup\$ Okay, but would that damage the battery? I mean the current is not supposed to flow through the battery in this direction \$\endgroup\$
    – Michael Brown
    Commented Aug 17, 2023 at 17:50
  • \$\begingroup\$ That's a good question. I'm not an expert in battery, so I wouldn't know. Usually the fault stay there so shortly and without drawing a lot of power (due to the voltage being too low) that I never had concerns with it. \$\endgroup\$
    – Julien
    Commented Aug 17, 2023 at 17:58
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    \$\begingroup\$ Yes, it will effectively try to charge the reversed cell with no current limiting. The best protection is to make sure your device won't operate unless it sees the equivalent voltage of four almost empty cells. This is good practice anyway to avoid fully discharging them. \$\endgroup\$
    – Finbarr
    Commented Aug 17, 2023 at 18:25

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