Introduction: Battery Guard

About: electronic beginner + Do things for fun, interest, play My answer is only from my own knowledge as status beginner and the internet search engine

The idea is to use a battery's condition - charged or not, to get, by the volt difference, a kind of trigger signal to turn on and off external devices, like led-lights or heatgrips.

My motorcycles battery has about 12.7 volts if not charged and about 13.7 volts if the motor running.

I asked in a Danish forum how to solve it, Jan from the Dansk Elektronik Forum made a electric diagram how it could be done. I decided to use the with the mosfet IRF 540 becaus that I had lying around.

Step 1: Building/soldering the Battery Guard From Elec​tric Diagram

Parts I used :

  • PC817 Opto-Coupler
  • IRF 540 Mosfet
  • 12 v Zener Diode
  • 1 x 100 ohms resistor
  • 1 x 10 k ohms resistor
  • 2 screw terminal
  • some stripboard

You can se on the schematic how the connection are and the pictures show you how it look like.

After soldering you can test with a multimeter and adjustable bench power supply. Now we got our kind of trigger signal.

Step 2: The on and Off Device

With the trigger signal you can drive for example a relay to turn on and off. But I found on gearbest that :

a Trigger Switch Driver Module with Dual MOS Tube / PWM

That is my solution.

After I usede it I found out that the battery still got over 12.7 volts after I stopped the engine. The lights was still on.

So I mounted a diode In4004 between 12v power source and the battery guar, so the diode gives a voltage drop of ca. 0.7 volts enough to turn off.