How to Make a Clamp-on Ammeter

Testing voltage levels takes special equipment.

Clamp- on ammeters are used to measure the current that runs through electronics. The ammeter is sometimes misspelled and mispronounced as an "ampmeter." An ammeter works by passing electric current through the shunt, or clamp, that is part of the ammeter design. Ammeters are designed to measure small amounts of current, such as the current that would pass from an electrical outlet to a toaster. You may want to measure the current passing through electronics to troubleshoot operational problems.

Things You'll Need

• Enameled wire
• Split ferrite core
• Plastic casing for the ferrite core
• Utility knife
• Load resistor or detector
• 2 Schottky diodes
• PCV insulating tape or epoxy
• 100mA range ammeter
• Scrap wood or other insulated, solid material
• Hot glue gun with glue sticks

Instructions

1. Wrap the enameled wire around the bottom half of the ferrite core ten times.

2. Fit the ferrite core into the plastic case. Adjust the case as needed to for the wire-wrapped ferrite to fit inside and still close. You may need to use a utility knife to scrape or hallow out the inside of the case to make it big enough to hold the wire-wrapped core.

3. Twist the wires from the core with the load resistors. Keep the leads short. The circuitry will require a series of resistors and diodes before connecting to the ammeter in order for the amps to properly measure on the meter. Cover the wrapped wire with PVC tape or epoxy to prevent damage during use.

4. Attach the core leads to the ammeter.

5. Glue the plastic case and ammeter to the board or insulated material. Keep the components close enough together to prevent adding strain to the connective wiring.

Tips & Warnings

• This type of ammeter is meant to be attached and left on to the electronic wiring being tested but with care, the plastic carrier can be reopened and reused.

• This clamp on ammeter is not calibrated. That means the results will be inaccurate until you calibrate it.

• Anytime you work with live electrical current, you should take precautions to stay safe. Attaching your clamp and ammeter to a wood block or other insulated material is the first step, but you should also make sure to discharge the circuit before connecting or discharging the ammeter from a cable. Safeguard against static buildup and avoid leaving an ammeter hooked up in reach of small children.

• Always connect an ammeter as part of a series connect, not as a parallel connection.

• Avoid using an ammeter near a strong magnetic field.

References

• All About Circuits: Ammeter Impact on Measured Circuit
• IFWtech Limited: Clamp-on RF Current MEter
• Integrated Publishing: Ammeter Safety Precautions