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I have built the attached Li-On Battery charger based on MCP 73831 chip and it works well. However I would like to add a reverse polarity protection to it since I've burned 2 chips while putting the battery to be charged the wrong way. Is there a reliable way to do this and sorry for my poor english language.

Thanks.

enter image description here

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  • \$\begingroup\$ Schottky diode in series! You do however need to move the voltage feedback point to behind the diode which in many cases is not possible. \$\endgroup\$
    – winny
    Commented Jan 9, 2017 at 22:37
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    \$\begingroup\$ Use a polarized connector so that this does not continue to happen. Also, I connect batteries to power supplies all the time. I don't think I have ever done it backwards. It seems a bit surprising that you have done it twice. \$\endgroup\$
    – user57037
    Commented Jan 10, 2017 at 4:32

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I have not seen electronic polarity protection on lithium batteries. Normally a polarized connector is used so that it is not possible to connect the battery with reverse polarity. Barring that, I would think that red/black color coding would be enough to prevent reverse polarity connections.

But if you REALLY want a circuit solution, here it is.

battery-reverse-polarity-protection

Q1 should be a PMOS FET with low Rds(on) at 2.7V. One possibility is alpha and omega p/n AO3401A. Q2 can be a 2n3904 or any typical logic BJT.

Note that this circuit will prevent a totally dead battery from charging. The battery must be at least 0.6V or so to turn on Q2.

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  • \$\begingroup\$ Q2 could also be an NMOS FET such as a BSS138, but then the turn-on voltage would be even higher. \$\endgroup\$
    – user57037
    Commented Jan 10, 2017 at 7:21
  • \$\begingroup\$ "Note that this circuit will prevent a totally dead battery from charging" - Good. If a Lithium-ion cell reads less than 2.5V then it is permanently damaged and not safe to recharge. \$\endgroup\$
    – Bruce Abbott
    Commented Jan 10, 2017 at 8:43
  • \$\begingroup\$ Thanks a lot guys. I'll put the mofdification suggested by mkeith and let you know how it goes. \$\endgroup\$
    – Eddy
    Commented Jan 10, 2017 at 9:08
  • \$\begingroup\$ @BruceAbbott, yeah but a protected cell may present itself as "dead" even though the internal cell voltage is above 2.5V. \$\endgroup\$
    – user57037
    Commented Jan 10, 2017 at 22:52
  • \$\begingroup\$ Li-Ion cells are NOT damaged by going below 2.5v, though they may loose some capacity. But they should be trickle-charged back up to 2.5v before applying a regular charge current. This is to prevent lithium plating on the anode. That is also a danger when charging any Li-Ion cell while cold. Cells should also be monitored for heat buildup when charging at any rate over 0.5A. \$\endgroup\$
    – Guy Gordon
    Commented Oct 23, 2020 at 3:33
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The "ideal" solution would be adding an ideal diode circuit. You could also use mechanical reverse polarity protection by using connectors that can't be reversed.

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