what is the Best Reverse polarity protection circuit for battery?

Submitted by Bradyen on Tue, 09/18/2018 - 11:15


I have just finished building a crude charger for my 12V 9Ah Lead Acid battery using LM317. Everything works perfectly but I need to have a reverse polarity protection circuit for my charger since it will be handled by novice people. 

Please suggest me a circuit which is simple and effective.I looked at few circuits but I am confused to use them since my load is a battery 


Hi Violet, thanks for the quick reply.

But I have already looked at the option of using a schottky diode. These diodes have roughly 0.4V drop across them and my charger has a charging current of 1.5A which is

P = 0.4 * 1.5 = 0.6W of loss in form of heat 

So I am looking for an alternative. 

  Joined August 14, 2018      44
Tuesday at 03:25 PM

Thanks Aswinth, on the first look I could not understand how th circuit works. But will google for more info and try it out on my test board. If everything works I am going to use it for my charger.

Thanks Again!

  Joined August 14, 2018      44
Tuesday at 03:25 PM

Using a MOSFET is a good idea, but is would just like to share one more option that uses a commonly available diode and fuse. Simple connect the diode in parallel to the charger output so that the conducts only if the battery is connected in reverse polarity also add a fuse in series to it.

So when then battery is connect wrong the diode will conduct safeguarding the charger and a high current will pass through it, since there is a fuse in series with it the high current will blow the fuse and open all connections. The circuit is shown below



As I told this circuit is very simple, but has its own downsides. One is that you have to replace the fuse every time there is a reverse polarity and the other is during reverse polarity the battery terminals are shorted periodically till the fuse is blown. This short is okay for Lead acid batteries, but should be avoided for lithium batteries 

  Joined September 07, 2017      256
Thursday at 12:15 PM