Short Tracer

Overview

Tracing shorts without high precision multimeter is very difficult if not impossible. This is because cheaper multimeters cannot measure resistance precisely enough, so it is impossible to locate the short very accurately.

I was looking at purchasing a 5-digit multimeter at a cost of around 160 €. This is more or less the price that one would be looking to get enough precision to locate a short.

However: even cheap multimeters can have quite high precision when it comes to voltage. You cannot use that directly to find the short, but with this tool you can.

How does it work?

The tool goes inline with the multimeter: one end connects to the multimeter, and the multimeter probes connect to the other end. All connectors are standard, gold plated 4mm banana jacks.

The tool then provides constant voltage and constant current. With the probes, you choose the places where to inject the current. The multimeter then measures the voltage drop and essentially turns the voltage drop across the resistance at the constant current into measure of how close you are to the short.

The smaller the measured voltage drop, the closer you are to the short. If you literally short the probes, that is the closest distance, and you should see smallest possible voltage drop at your multimeter. Now if you measure something else, like a piece of wire, you should see larger value; you have gone further away from the short.

Battery powered

Both voltage and current can be set with variable resistors. The upper voltage depends on the battery voltage, but the operational range is approximately from 1.5V to 2.5V, or from 1.5V to Vbat – 1.2.

Constant current is voltage dependent, but it can be set approximately between 15mA and 150mA. Set the voltage first, and then set the current.

Setting voltage and current

VR1 adjusts the voltage while VR2 adjusts the current.

You might want to use lowest possible voltage unless that is not enough; low voltage reduces the risk of accidentally damaging anything.

What’s included

Includes assembled Short Tracer; cables nor the battery are included. You will need a nominal 4.2v 18650 lithium ion battery and a 4mm male-male banana cables. And of course your multimeter probes.