USB Charging Troubleshooter

Project List of Materials

1. Mini Digital Voltmeter Ammeter DC 100V 10A Panel Amp Volt Voltage Current Meter
2. USB Cable approx 1m length
   • Option 1: 1m USB 2.0 Extension Cable (Type-A Male to Type-A Female)
   • Option 2: Momax 1.2m 4 in 1 Type-C PD Cable (USB-A/USB-C to Micro USB/USB-C)
3. 3D Printed Case
4. 10mm cable zip ties x 2
5. Electrical insulation

Note:

1. Not all USB cables are the same. Make sure you stick closely to the specifications above to ensure the wiring is correct.
2. There are two different options provided above dependent of what your preference of USB cable to test. In practice, I have built both to cover USB A, C and B Mini which covers most common applications.

Required tools

1. Hot glue gun
2. Soldering iron
3. Wire strippers
4. Wooden chopping board
5. Box cutter knife

The case has been specifically designed to enable a cable to enter and exit the case to ensure the minimal necessary wires are required to be cut. Therefore the cable presses into the cable slot on the back of the unit with the back lid pressing into position to clamp the cable into the unit.

The case 3D printable STL files can be found here

Preparing the USB cable

1. Lay the cable in the case and create a bend in the cable to provide some slack.
2. Create a "chord restraint" by using 2 x cable ties to secure each end of the cable. These also help retain the slack in the cable.
3. Remove the cable from the case and place it on a wooden chopping board or firm surface. Using the box cutter knife carefully slice a single line in the exterior cable insulation between the cable ties. Note: take care to just go through the exterior insulation so as not to damage the wires in the cable.
4. Pull back the exterior insulation and cut this off exposing the braided shielding around the wiring. Using your fingers only, part the external braiding and expose the interior wires The interior wires are usually covered in a tin foil shield so carefully unravel this and expose the RED and Black wires in the cable.
5. Carefully cut these two wires then use your wire strippers to remove 5mm of insulation off each end. For each end of the RED and Black wires, Gently twist the copper wire then use the soldering iron to tin the ends.

Voltmeter Meter Plug

The Digital Voltmeter unit comes with two cables with different plugs.

1. The smaller plug comes with three wires (Red, Black & Yellow) and is used to monitor the voltage on Red the USB cable wire. In this project the black wire is not used so is cut short and carefully insulated.
2. The Red and Yellow are shortened to approx 5cm and then joined as per the picture provided.
3. Carefully attach the Red and Yellow Voltage Meter wires to the two exposed red cable wires and solder all four together ensuring there is a good strong connection.
4. Use heat shrink to insulate any exposed areas of the joint.

Current Meter Plug

The larger plug with two wires (Red and Black) are used to monitor current. Current is measured by placing a very low-value resistor in line with the earth cable and then measuring the voltage across the resistor. This is reported as current on the digital readout. We do this by placing it in line with the USB cable earth wire (Black).

1. Shorten the Red and Black Current Meter Plug wires to 5cm and 3cm respectively.
2. Use your wire strippers to remove 5mm of insulation off each end. For each end of the RED and Black wires, Gently twist the copper wire then use the soldering iron to tin the ends.
3. Carefully attach the Black Current Meter Plug wire to the black USB cable wire associated with the USB Male connector. Solder the two wires together ensuring there is a good strong connection. Use heat shrink to insulate any exposed areas of the joint.
4. Carefully attach the Red Current Meter Plug wire to the black USB cable wire associated with the USB Female connector. Solder the two wires together ensuring there is a good strong connection. Use heat shrink to insulate any exposed areas of the joint.

Test before assembly

1. Prior to fully assembling the case it is worthwhile quickly connecting up to the Digital Meter and testing everything is working.
2. Take a USB charger and connect one end of the cable to the charger.
3. This should result in the Voltage being displayed.
4. If this works then try attaching a device to the other end of the cable to see the current is displayed.
5. If there are issues remove any connectors to devices or charging units and go back and check the wiring in the previous steps.

Final Assembly

1. Following successful testing use insulation tape to cover any exposed shield wires to ensure they don't short out the circuit board when fully assembled.
2. Identify the most appropriate orientation of the Digital Meter so that it aligns with the wiring before pushing into the front of the case, it will click into place.
3. Carefully lay the cables into the back of the unit and connect the wires.
4. Use hot-glue to secure the cable and the back of the case into place and ensure it is firmly held in place.

The nature of USB charging is complicated by the various different USB standards and cable types which makes compatibility of devices, cables and chargers a challenge.

Most chargers use 5v however fast charging can involve increasing this supply voltage to 9v and s triggered by the device essentially negotiating with the charger via the cable.

Over the charging time of the device, you will notice the current slowly reduce to zero as the smart charging circuitry in the device regulates the charging process to avoid device and battery damage.

Most USB 2 device will charge with up to 1amp of current where a fast charge configuration will drive currents over 1amp.

Charger Comparison Technique

Using the USB Charging Troubleshooter device can help identify the normal behaviour of your devices with the correct charger and cables so you can compare device, cable and charger performance.

I used it this way to demonstrate the failure of Fast Charging on a friend's faulty cable for his Samsung phone who had intermittent charging issues.

Damaged Wires

You can also connect the charger to a device via the troubleshooter and by carefully manipulating the cable at each end to identify bad or broken connections which will show up as low voltage or current during charging.

Damaged Device Batteries

Over the charging time of the device, you will notice the current drop. If it stays low or high for longer than the charge cycle and does not retain its charge then it is likely a damaged device battery.

Happy troubleshooting !!