Vehicle Charge Indicator

Not every vehicle is equipped with equipment that tells you that the charging system is not working. That is certainly true for several of my vehicles. So decided to think of a way to monitor the charging system, but since I do not want some kind of big, expensive, ugly device for this, I decided that I should just make a simple solution with a LED and some kind of small circuit board. So I came up with this.


Look how small it is! 10pcs PCBs ready for a LED in one end and a Power cable on the other. The green and red LEDs are 3mm, and the blue and yellow are 5mm. The bigger ones are 8mm and 10mm, and gets more visible, but require a bigger mounting hole.

This can be used on Cars, Motorcycles, Mopeds, ATVs, Boats, Tractors, Snowmobiles, Snowblowers, Lawn mowers etc. anything that have a charging system. 6v, 12v and 24v versions can be made from the same PCB.

Its simple. If the alternator is charging, the LED lights up. No light, no charge. The design is made so that you can connect it directly on the battery or on the output from your rectifier, and it will not drain any power while the vehicle is not in use. There is no fuse, so you might want to add one to the wire. The circuit can handle reverse voltage for a while, but sooner or later the diode will break down, so try to connect positive to positive and negative to negative.

The idea is that with only a small hole somewhere suitable on the vehicle, one could drill a hole for one LED, ranging from 3mm to 10mm depending on available room and personal preference. I wanted the device to be as small as possible, so I went with SMD parts, to save space. Just for fun, Im gonna try to post this device on ebay, but if you rather want to make your own, I will let you know how it works, and list the parts you need.


D1: 12v Zener Diode
R1: 56 Ohm Resistor
D2: 1N4007 Diode
LED holder
Shrink tube

The theory is this:

We don’t want the LED to power on unless the vehicle is charging. So the power from the battery will be blocked by the Zener Diode (D1). But when charging is taking place, the voltage to the battery will be a raised from around 12v to around 14v. A normal charge would be from 13.7v to 14.7v. If you get less or more than that, you need to check your regulator. When the Zener diode (D1) reach the breakdown voltage generated by the charging system, power will pass through, and make the LED (L1) turn on. The resistor (R1) is there to protect the LED (L1). The resistor value can be changed according to how bright you want the LED to shine. D2 is there to protect from reverse voltage generated by the alternator.

For a 6v charging system, all you need to do is to replace D1 with a 6V Zener Diode.
For a 24v charging system, all you need to do is to replace D1 with a 24V Zener Diode.

This project with PCB and parts can be purchased on ebay:

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