FNIRSI FNAC-28 USB Cable Resistance Testing Guide Malaysia

FNIRSI FNAC-28 USB Cable Resistance Testing Guide Malaysia

Introduction

USB charging cables are widely used with smartphones, tablets, power banks, portable electronics and many other devices. Although most USB cables look similar, their electrical performance can vary significantly.

A poor-quality USB cable may cause slow charging, excessive voltage drop, unstable power delivery or connector heating.

For electronics technicians and repair workshops, measuring USB cable resistance is one practical way to investigate these problems.

The FNIRSI FNAC-28 USB Tester provides cable resistance testing functions that can help users compare charging cables under suitable test conditions.

This guide explains how USB cable resistance affects charging performance, how to conduct practical comparisons and how to interpret measurement results.

1. What Is USB Cable Resistance?

Every electrical conductor has some resistance.

In a USB charging cable, electrical resistance comes from the conductors, connectors and electrical contacts.

Resistance is measured in ohms, represented by the symbol Ω.

When charging current flows through a cable, resistance causes a voltage drop.

The relationship is described by Ohm's Law:

Voltage Drop (V) = Current (A) x Resistance (Ω)

For example, if the total resistance of a cable's power path is 0.2 ohm and the charging current is 2A:

Voltage Drop = 2A x 0.2 ohm = 0.4V

This means the voltage at the receiving end of the cable may be approximately 0.4V lower than at the source under those conditions.

Lower cable resistance generally helps reduce voltage drop and resistive power loss during charging.

However, resistance alone does not determine overall USB cable quality. Connector reliability, insulation, data capabilities and supported charging current are also important.

2. Why Is USB Cable Resistance Important?

Cable resistance becomes particularly important when charging current increases.

For example, a cable carrying 3A experiences a greater voltage drop than the same cable carrying 1A, assuming its resistance remains approximately constant.

Excessive cable resistance can contribute to several problems.

Slow Smartphone Charging

A charging cable with high resistance may reduce the voltage reaching the connected device.

Depending on the charging system, the device may respond by reducing charging current.

Unstable Charging

Poor connectors or damaged conductors may create intermittent electrical connections.

This can cause charging interruptions or fluctuating measurements.

Reduced Charging Efficiency

Electrical energy is lost as heat when current flows through resistance.

The relationship is:

Power Loss (W) = Current² (A²) x Resistance (Ω)

Higher resistance produces greater power loss at the same current.

Connector Heating

Loose or contaminated electrical contacts can create additional resistance.

Under high-current conditions, this may result in excessive local heating.

Important: Stop using any cable or connector that becomes unusually hot, smells burnt or shows signs of damage.

3. FNIRSI FNAC-28 USB Cable Testing Features

The FNIRSI FNAC-28 USB Tester is designed for USB electrical measurements and selected charging-related diagnostic functions.

FeatureDescriptionModelFNIRSI FNAC-28Instrument TypeUSB Digital TesterVoltage Measurement4V to 24VCurrent Measurement0A to 6.5AMaximum Rated Power156WUSB ConnectionsUSB-A and USB Type-CCable TestingCable Resistance ComparisonCharging MeasurementsVoltage, Current and PowerAdditional FunctionsSelected Fast-Charging Protocol TestingTypical UsersElectronics Technicians and Repair Workshops

The USB cable resistance testing function can assist users in comparing cable performance.

For meaningful results, the correct test method must be followed and measurement conditions should remain consistent.

4. How to Test USB Cable Resistance with FNIRSI FNAC-28

The following procedure describes the general principles of cable resistance comparison.

Users should follow the FNIRSI operating manual for the specific resistance test mode, connection arrangement and display instructions.

Step 1 - Prepare a Compatible USB Power Source

Use a stable, compatible USB charger within the tester's operating limits.

Inspect the charger and connections before beginning.

Step 2 - Select a Suitable Test Load

A compatible electronic load or other stable load can help provide repeatable test conditions.

For meaningful cable comparisons, use the same load conditions throughout the testing process.

Step 3 - Establish a Reference Measurement

Where required by the manufacturer's procedure, establish a reference measurement before inserting the cable being evaluated.

A reference helps distinguish the cable's contribution from the voltage losses caused by the power source, tester and other connections.

Step 4 - Connect the Cable Under Test

Connect the USB cable according to the tester's supported cable resistance measurement arrangement.

Ensure that all connectors are firmly seated.

Step 5 - Perform the Resistance Test

Use the FNIRSI FNAC-28 cable resistance testing function according to the manufacturer's instructions.

Record the indicated resistance value.

Step 6 - Compare Different Cables

Repeat the measurement with other cables while keeping the power source, load and connection conditions as consistent as possible.

A lower measured resistance may indicate a lower-resistance power path.

Important: The displayed result may include connector and contact resistance. It should not automatically be interpreted as the resistance of the copper conductors alone.

5. USB Cable Resistance and Voltage Drop

Understanding voltage drop is essential when evaluating USB charging cables.

The following table shows theoretical voltage drop for different resistance values.

Total Cable Path ResistanceVoltage Drop at 1AVoltage Drop at 2AVoltage Drop at 3A0.05 Ω0.05V0.10V0.15V0.10 Ω0.10V0.20V0.30V0.20 Ω0.20V0.40V0.60V0.30 Ω0.30V0.60V0.90V0.50 Ω0.50V1.00V1.50V

These values are calculated examples, not official FNIRSI measurement results or USB cable pass-fail limits.

The table demonstrates that higher charging current produces greater voltage drop across the same resistance.

For example, a cable with 0.30 Ω total resistance would theoretically experience a 0.90V drop at 3A.

This could significantly affect a 5V charging connection.

However, actual charging behaviour depends on the charger's voltage regulation, the device's power management and the negotiated charging mode.

6. Comparing Cheap and High-Quality USB Cables

Two USB cables may look almost identical but perform differently under electrical load.

Consider the following hypothetical comparison.

ParameterCable ACable BCable Length1 Metre1 MetreMeasured Path Resistance0.10 Ω0.35 ΩTest Current2A2ACalculated Voltage Drop0.20V0.70VCalculated Resistive Power Loss0.40W1.40W

Under these conditions, Cable A has lower resistance and lower calculated power loss.

This suggests Cable A may be better suited for carrying the same charging current with less voltage drop.

However, USB cable quality cannot be judged by resistance alone.

Other considerations include:

Connector durability

Cable insulation

Supported charging current

USB data transfer capability

USB-C electronic marker requirements

Mechanical construction

Manufacturer specifications

A cable with low resistance is not automatically certified for high-power USB-C charging.

7. Does USB Cable Length Affect Charging Performance?

Cable length can influence electrical resistance.

For cables made from the same conductor material and cross-sectional area, a longer conductor generally has greater resistance.

The relationship is:

R = ρL / A

Where:

R = Electrical resistance

ρ = Material resistivity

L = Conductor length

A = Conductor cross-sectional area

This explains why longer cables may produce greater voltage drop when other construction characteristics remain equal.

However, a well-designed longer cable with thicker conductors may have lower resistance than a shorter cable using thin conductors.

Therefore, cable length alone is not sufficient to determine charging quality.

The FNIRSI FNAC-28 can help users compare the electrical behaviour of compatible cables.

8. How to Identify a USB Cable Causing Slow Charging

A technician investigating slow charging can use the following approach.

Test 1 - Check the Charger

Measure charging voltage and current using a compatible charger and device.

Record the readings.

Test 2 - Use a Known-Good Cable

Replace the original cable with a suitable known-good cable.

Keep the charger and connected device unchanged.

Test 3 - Compare Charging Performance

Observe any differences in voltage, current and power.

If charging performance improves with the known-good cable, the original cable may require further investigation.

Test 4 - Compare Cable Resistance

Use the FNAC-28's supported cable resistance test function to compare the cables.

Test 5 - Inspect the Connectors

Check for loose contacts, damaged connectors, corrosion or contamination.

Important: A cable with abnormal resistance should not be repaired or reused for high-current charging without appropriate safety verification.

9. USB Cable Resistance vs USB Charging Power

Cable resistance influences electrical losses, but it does not directly determine the charging power selected by the device.

For example, a smartphone may limit charging current because of battery temperature even when the USB cable has very low resistance.

Likewise, a cable may have low resistance but lack the required USB-C electronic marker or other characteristics needed for a particular high-power charging mode.

Therefore, technicians should evaluate:

Cable Resistance: Electrical resistance of the power path.

Charging Voltage: Voltage available during charging.

Charging Current: Current flowing through the connection.

Charging Power: Voltage multiplied by current.

Protocol Compatibility: Whether the charger and device support compatible charging modes.

A combination of these measurements provides a more complete understanding of charging performance.

10. Can FNIRSI FNAC-28 Test USB-C Cable Quality?

The FNIRSI FNAC-28 includes USB Type-C connectivity and supports compatible USB charging measurements.

Its cable resistance function can help evaluate the electrical performance of supported USB cable configurations.

However, USB-C cables may differ in their current ratings, electronic marker information, USB data capabilities and supported charging modes.

The FNIRSI FNAC-28 should not be treated as a complete USB-C cable certification instrument.

For professional verification of USB-C compliance, high-speed data performance or detailed electronic marker capabilities, specialised testing equipment may be required.

11. Common USB Cable Testing Mistakes

Several testing mistakes can produce misleading results.

Using Different Chargers

Different chargers may have different output characteristics.

For accurate comparisons, use the same stable power source.

Using Different Loads

Charging current changes with the connected device's demand.

Use consistent loading conditions whenever possible.

Ignoring Connector Resistance

Dirty or loose connectors may increase measured resistance.

Inspect the connectors before testing.

Comparing Different Cable Types Without Context

A USB-A cable and a USB-C cable may have different construction and supported functions.

Compare cables intended for similar applications.

Treating Resistance as a Complete Quality Rating

Low resistance does not guarantee good data transmission, safe high-power operation or long-term mechanical durability.

12. Applications of USB Cable Resistance Testing in Malaysia

The FNIRSI FNAC-28 USB Cable Resistance Tester Malaysia can support several practical applications.

Mobile Phone Repair Shops

Technicians can compare charging cables when investigating slow or intermittent charging.

Electronics Retailers

Retailers can demonstrate differences in electrical resistance between compatible charging cables.

Computer Service Centres

Service technicians can investigate USB power delivery problems affecting portable accessories.

Electronics Training Centres

Students can learn how electrical resistance influences voltage drop and power loss.

Electronics Hobbyists

DIY users can compare USB cable performance for compatible low-voltage electronic projects.

13. Where to Buy FNIRSI FNAC-28 USB Tester in Malaysia?

MTM Precision Sdn Bhd supplies electronic testing and measuring instruments for technical and professional applications.

Customers looking for a FNIRSI FNAC-28 USB Tester Malaysia can contact MTM Precision for product enquiries, pricing and availability.

The FNAC-28 is suitable for users interested in USB charging measurements, cable resistance comparisons and general USB power troubleshooting.

MTM Precision serves customers throughout Kuala Lumpur, Selangor, Johor, Penang, Melaka, Negeri Sembilan, Perak, Pahang, Kedah, Kelantan, Terengganu, Perlis, Sabah and Sarawak.

Please contact our team to confirm current stock and delivery arrangements.

Frequently Asked Questions

Q1. Can FNIRSI FNAC-28 measure USB cable resistance?

Yes. The FNIRSI FNAC-28 provides a cable resistance testing function for supported test arrangements.

Q2. What does high USB cable resistance mean?

Higher resistance generally produces greater voltage drop and resistive power loss at the same charging current.

Q3. Does a longer USB cable always have higher resistance?

Not necessarily. Cable resistance also depends on conductor material, conductor thickness and construction quality.

Q4. Can FNIRSI FNAC-28 identify a faulty USB cable?

It can help identify abnormal electrical resistance and charging behaviour. However, it cannot detect every possible cable fault.

Q5. Can low cable resistance guarantee fast charging?

No. Fast charging also depends on the charger, device, charging protocol and cable capabilities.

Q6. Is FNIRSI FNAC-28 suitable for USB-C cable testing?

It can support compatible USB-C charging measurements and cable resistance comparisons, but it is not a complete USB-C compliance tester.

Q7. Where can I buy FNIRSI FNAC-28 in Malaysia?

Contact MTM Precision Sdn Bhd in Puchong, Selangor, for product enquiries, pricing and availability.

Contact MTM Precision Sdn Bhd

For FNIRSI FNAC-28 USB Tester Malaysia, USB cable resistance testing equipment and electronics measuring instrument enquiries:

MTM Precision Sdn Bhd

Showroom & Service Centre

No. 29-1 & 29-2, Jalan Bandar 18,

Pusat Bandar Puchong,

47160 Puchong, Selangor, Malaysia.

Tel: 03-8080 7172

WhatsApp: +6016-660 7346

Email: mtmpre@yahoo.com

Website: www.mtmpre.com.my

Contact MTM Precision today for FNIRSI FNAC-28 pricing, availability and USB cable testing instrument recommendations in Malaysia.

Conclusion

USB cable resistance is an important factor affecting charging voltage, power loss and overall charging performance.

The FNIRSI FNAC-28 USB Tester provides useful functions for comparing cable resistance and monitoring USB charging conditions.

By understanding Ohm's Law, voltage drop and resistive power loss, technicians can better investigate slow charging problems and compare compatible USB cables.

For customers searching for a USB Cable Resistance Tester Malaysia, USB Cable Quality Tester Malaysia or FNIRSI FNAC-28 Malaysia, MTM Precision Sdn Bhd can assist with suitable product enquiries and testing instrument selection.