It can be used to safely measure low voltages such as train sets, battery devices or car electrics. Start by disconnecting the appliance from the mains, and it should be safe to measure the resistance of components and devices, helping you identify where a problem is occurring..
* Please note: we do not advise the handling of switched-mode power supplies or microwaves, as these appliances can retain a large electrical charge that can still be dangerous if a fault exists for some time after being disconnected. *.
To use the resistance readings, set the meter to the correct range and calibrate if necessary. If possible, disconnect the wires to the component and measure the dc resistance across it. If the reading is not within 10% either way of the expected value then the component is likely to have failed (make sure motors are not seized and turn freely).
It is sensible to avoid live mains electricity and we would not recommend live electrical fault tracing; the multimeter should be able to identify most problems with just the resistance reading across the suspect component.
What resistance readings should I expect?
Here below are some common resistance readings in domestic appliances designed for running on 230 volts
Heater elements in dryers, cookers, washing machines etc.
Typical 2kw 26.5 ohms1kw element 53 ohms 500 watt element 106 ohms
Pump motor 165 ohms
Main motor ( Brush type )
Armature Between 1.5 ohms and 5 ohms on a washing machine (depends on power & spin speed)
Field windings Between 1 and 5 ohms on a washing machine (depends on power & spin speed).
Tacho coil typically 120 ohms approx.
Thermal cut out less than .1 ohms when closed (not cut out).
Sensor on wash heater20,000 ohms at 20 degrease C 5000 ohms at 60 degrease C 1300 ohms at 95 degrease C
Bear in mind the resistance readings are directly related to the power used by the device.
For example a 15 watt mains bulb in a fridge would read approximately 3450 ohms
But a 150 watt mains bulb would read 10 times lower at approximately 345 ohms
The resistance of 15 watt bulb designed for a 12 volt system would be 9.6 ohms
And for a 150 watt bulb designed for a 12 volt system the resistance would be 10 times lower at .96 of an ohm
The above readings are given as a guide and may change depending on manufacturer.
* All information provided is a guide only. BuySpares accepts no liability for any problems occurred while attempting any advice shown. If in any doubt contact a qualified repair service.