In high-current circuits, how can a voltage drop tester accurately capture changes in micro-ohm-level contact resistance?

Publish Time: 2026-02-04

In high-power systems such as new energy vehicles, rail transit, power distribution, and industrial automation, the reliability of electrical connections directly affects the safety and lifespan of equipment. These systems often operate under high current conditions of hundreds or even thousands of amperes. Even an abnormal resistance of a few microohms at the contact point can cause localized overheating, performance degradation, or even fire risks due to the Joule heating effect. Accurately identifying and quantifying these "invisible" micro-ohm level changes in contact resistance has become a core issue in ensuring the safety of high-current circuits. The voltage drop tester is a key testing tool developed for this purpose.

1. Four-wire measurement: Eliminating lead wire errors and directly measuring the true voltage drop

When measuring resistance using the traditional two-wire method, the resistance of the test leads themselves is superimposed on the measured object, leading to severely distorted results—especially at the micro-ohm level, where the lead wire resistance may far exceed the measured value. The voltage drop tester employs a four-wire measurement principle, separating current injection from voltage sampling: a pair of high-current leads apply a stable test current to the circuit under test, while the other pair of high-impedance voltage sensing leads are directly connected across the test contact point, acquiring only the voltage drop signal without current flow. This completely eliminates the influence of lead resistance and contact resistance on voltage measurement, achieving high-fidelity capture of the true contact voltage drop.

2. High-current excitation: amplifying the signal and improving the signal-to-noise ratio

The voltage drop generated by a micro-ohm resistor under normal low current conditions is extremely weak and easily drowned out by environmental noise. The voltage drop tester, through its built-in high-stability constant current source, injects tens to hundreds of amperes of DC current into the circuit under test for a short time, "amplifying" the weak resistance signal into a precisely measurable millivolt-level voltage. For example, when the contact resistance is 5μΩ and the test current is 100A, the voltage drop reaches 0.5mV—a signal sufficient for accurate capture by a high-resolution ADC. Meanwhile, modern instruments generally employ synchronous sampling, digital filtering, and multiple averaging algorithms to further suppress electromagnetic interference and ensure measurement repeatability better than ±0.5%.

3. Dynamic Response and Temperature Drift Control: Addressing Real-World Challenges

During high-current testing, the conductor's own heating causes its resistance to change with temperature. High-end voltage drop testers not only have rapid sampling capabilities but can also capture transient voltage drops within the current stability window, avoiding thermal interference. Furthermore, key components such as precision shunts and operational amplifiers use low-temperature drift materials and are equipped with internal temperature compensation algorithms to ensure full-range accuracy within the 0°C to 40°C operating range. Some models also support pulsed high-current output, meeting testing requirements while preventing overheating of the tested component.

4. Application Scenario Verification: From Battery Connectors to Busbars

Taking electric vehicle battery packs as an example, if there are poor solder joints or loose bolts in the copper busbar connections between modules, the contact resistance may rise from the normal 2–3 μΩ to over 10 μΩ. Applying a 100A current using a voltage drop tester results in a normal connection voltage drop of approximately 0.2–0.3mV, while abnormal connections show a jump of over 1mV, making the difference significantly noticeable. Similarly, this technology has become a standard preventative maintenance method at critical points such as the DC side of photovoltaic inverters, data center UPS buses, and high-speed rail pantograph contactors.

In summary, the voltage drop tester, with its four-wire architecture, high-current excitation, low-noise design, and environmental adaptability optimization, successfully transforms "micro-ohmic level hazards" into "visible and verifiable data," constructing an irreplaceable technical defense line for the safe operation of high-current systems.