Measuring current

On a vehicle, it is relatively rarely necessary to measure current. Example: see the section "Battery discharges itself". An ammeter is required for this, which is also integrated in a multimeter.

Before measuring current, set the meter to the measuring range in which the current to be measured is expected to lie. If this is not known, set the highest measuring range and, if no reading appears, switch to the next lower measuring ranges one after another.

To measure current, the circuit must be opened and the meter (ammeter) connected in series. To do this, for example, disconnect the connector and connect the red lead (+) of the ammeter to the live wire. Connect the black lead (-) to the contact to which the interrupted wire is normally connected. The ground contacts between the consumer and the connector must then be bridged with an auxiliary cable.

Caution: under no circumstances should a standard ammeter be used to measure the current in the wire to the starter (approx. 150 A) or to the glow plugs on diesel engines (up to 60 A). The high currents involved can destroy the meter. The workshop uses a DC current clamp ammeter for these measurements.

For this, a current clamp is clamped around the insulated power cable and the current value is measured by induction.