How to check the electric motor with a multimeter: a review of 5 AC motor designs with photos
Recently I often have friends and neighbors began to ask: How to check the electric motor multimeter? So I decided to write a short tutorial for beginner electricians.
I’ll note right away that one multimeter does not allow you to identify with a 100% guarantee all possible malfunctions: few of its functions. But about 90% of defects can be found with it.
I’ve tried to make the instructions universal for all types of AC motors. The same techniques with a thoughtful approach can be used in DC voltage circuits.
Design and operation of the fan
The fan, regardless of the design, is the simplest household electrical appliance. The low power required to rotate the vanes has allowed the simplest and most dependable single phase induction motor without a commutator box to be fitted to the fan. This allows the motor to run quietly and without the need for periodic replacement of brushes.
To make the fan it is enough to fix the impeller on the motor shaft. When the supply voltage is applied, the motor shaft begins to rotate in a given direction and because of the curved shape of the blades, the air begins to move.
For safe and convenient operation the motor is placed in the housing and the blades are covered with a grid. The shape of the housing depends on where you install the fan. on a table, on the floor or in the ventilation shaft of the kitchen or bathroom.
A switch and a pushbutton or manual speed regulator are usually installed on the fan housing to turn on and adjust the air flow rate. There are fans with remote control, but they are usually twice as expensive as simple fans.
Causes of breakage
The smoke evacuator may be malfunctioning for the following reasons:
Pro Combi 100 HE How to Test the PCB or Fan Fault. With Coach Tony Morgan
- Inductance coil is damaged. The high temperatures resulting from removal of hot gases or motor overloading melt the insulation of the wire, causing inter-turn short circuits or winding breakdown of the coil.
- Turbine out of balance. The fan blades are covered with soot, dust, etc. in the process of smoke extraction. д., which causes the center of gravity of the wheel to change.
- Worn bearings. The armature shaft is fitted with sleeve bearings or. If the turbine is out of balance, insufficient lubrication, the service life of these units is reduced.
- There is no power to the smoke evacuator. The impeller will not rotate if the control board module responsible for powering the blower is defective.
- Low line voltage. When the electric voltage supplied to the boiler is less than 195 volts, the pressure switch may cut out the fan, since insufficient negative pressure is created due to reduced power. Low voltage on gas boiler supply does not cause fan failure, but causes malfunctioning effect.
Causes of tripping
The automatic control system can be triggered by various faults in the installation of the smoke evacuation structure, sensor parameters failure themselves.
Exhaust gas safety thermostat 70 °C
- Strong wind. A gust of wind can blow out the gas burner. To prevent this from happening, purchase a stabilizer for the unit and install it in place of the outlet.
- Clogged chimney system. In this case, cleaning will be necessary.
- Weak draft parameters. Traction sensor of the gas boiler reacts when heated 950-1500 ° C. Because of the complexity of smoke removal, there is overheating inside the smoke removal system and turning off the gas valve.
- Incorrect installation of gas equipment.
- Incorrect calculation of the dimensions of the chimney. The height of the chimney is measured depending on the distance of the pipe from the roof ridge. Recommended location. exactly in the center of the roof. In this case, the hatch will rise above the ridge of more than half a meter.
Elementary safety rules
Although the design of the circulating pump is simple enough, to fix the arisen failures will require a certain qualification. Therefore, it is easier to prevent the problem than to heroically fix it later. One of the signs that there is something wrong with the equipment, is its excessive heating during operation.
This can be prevented by following the simplest rules of operation:
- Under no circumstances may the wiring come into contact with moisture.
- Particular care should be taken to check the connections between the pump unit and the piping system for leaks. If leakage occurs, the gaskets must be replaced.
- The machine must not be switched on without first being grounded. The design of the heating pump includes special terminals.
- The internal pressure force must not exceed the operating limits.
Check ceiling Fan using Multimeter in hindi || ceiling fan winding kaise check kare with multimeter
To understand why the heating pump does not work, it is recommended to ask for help from a professional technician. The simplest problems you can try to fix yourself.
Floor fan does not spin
The most common problem is a dried up grease or lack of it. The fan begins to jam, loses speed and as a consequence, the load on the motor increases. The blower no longer operates at its full potential.
The engine, wound with a thin wire of 0.2 mm, begins to heat up and gradually burn out the winding.
How this defect is detected? In this case the fan stops rotating. It hums, but the impeller doesn’t rotate.
And sometimes it only starts in the 3rd speed and does not respond to the first two speeds. It just doesn’t have enough power to turn the shaft.
In order to start it, you have to crank the blades like on old planes.
By the way, the same symptom can also be when the starting condenser is damaged. How do you know without instrumentation, what is the cause of the failure?
To do that you have to at least get to the motor shaft by removing the guard and blades. If the shaft rotates with great difficulty by hand, then blame dirt and dried up grease.
And if it turns easily and has inertia, then it’s most likely that the capacitor is dead. The symptom. you have plugged in the fan, but it does not rotate. You crank the motor brazenly and it starts.
If hand holds fan blades during operation, fan may stall again. Check the capacitor with a multimeter, if it has the appropriate capacitance scale.
For replacement, select a new cooler with the same parameters as shown on the body of the old one.
By the way not completely dried out condenser also affects rotation speed. If you notice that they dropped and fan rotates slower, it is a bell to check it.
The problem of stiff rotation can be solved by relubricating the bearings. Here are used, so-called sliding bearings. Some people call them bushings.
It is expensive to use balls in such constructions and they rattle a lot with time. To repair it is not necessary to disassemble the entire engine. It is enough to unscrew a few screws and spray to the right places with WD40 universal spray.
How to make a fan heater with their own hands
Heaters are very popular and qualitatively perform the function of heating the room. The heat fan is arranged quite simply, and it is quite possible to make it with your own hands. Popularly, the fan heater is called a wind-blower, fan, breeze, wind-blower.
The main components of the fan heater are a heating element (ceramic or spiral), the body and the fan itself.
The most commonly used variety of fan heater is a heat gun. The main difference between a heat gun and a fan heater is the greater power of the device, the heat output and a longer service life.
Before you make a fan heater, you should find a diagram and watch a tutorial video
To make a heat gun, you will need:
- Channel fan;
- Thermostat and speed regulator;
- A frame to support the structure;
- The heating element (can be removed from an old, obsolete device, an old vacuum cleaner will do);
- Components for fasteners (bracket, clamp and others);
- The case (sheet of iron or a piece of pipe);
- Electric cable.
The step-by-step instructions for assembling a heat gun are simple. Preparation of the support and the gun body, installation of heating element (heating element). The wiring to the heating element, installation of the fan and supplying it with power is obligatory. Then comes the supply of all wiring to the control panel, the installation of protective grating in front and behind the enclosure for the free passage of air. Before using the gun, you need to make a test run of the device.
Repair of the blower heater with his own hands. scheme, causes of failure, thermal protection.
With the advent of the first cold weather, the main wand in the warming of our homes and offices, are not bulky oil radiators or convectors, and small and compact fan heaters.
They allow for a very short period of time to raise the temperature in the room at once by several degrees.
However as a result of operation, that is called at full speed, sooner or later comes the moment when the blower ceases to work. What to do in this case? Run to the store for a new Scarlet, Saturn or Comfort and hope that they are much more reliable?
After all they do not cost very much. However it is not necessary to buy another fan heater, if you can repair the existing one with your own hands.
In order to find the cause of failure you need only two things. a screwdriver and a multimeter.
The most important thing is to determine whether there is a contact in a circuit or not. Let’s take a closer look at how fan heaters are constructed, how to disassemble them, what usually breaks down and trace the successive chain of checks of one element after another.
The first thing to do is to check and check the continuity of the power cord and all visible contacts. Maybe you will not have to go far into the device internals, and the trouble will be on the “surface”.
To do this, unscrew and remove the bottom or side cover, depending on your model.
Keep in mind that the central screws initially do not unscrew, because they are attached to the motor.
Remove them and all the insides fall apart. It would be better to have the motor itself sitting attached to one of the covers.
Next, find the pins where the 220V power wires come. If you are “lucky”, sometimes without any instruments you can immediately see a burned out wire.
Put it in place and the repair is complete. If the problem is more serious just feel and twitch all the terminal clamps.
Since the fan vibrates during operation, it is quite possible that one of them has elementary moved out of place. It is possible to detect bad contact on the terminal block by characteristic traces of burning.
Often these defects are the reason that the fan heater turns on and off by itself. Especially when you move it and move it.
If you find something like this, clean and then wipe the pad with a cotton swab moistened with alcohol.
Then use pliers to gently squeeze the terminal and put it back on.
Only after all these manipulations, you can proceed to testing with meters.
Switching the tester to the continuity mode, and using the probes check the continuity of power wires one by one. To do this, touch the lead pins inside the fan and the metal pins on the plug.
If everything is fine, the tester will beep or show zero resistance.
If you have something working when you plug it in, like a fan spinning, but the air is cold, then of course the cord has nothing to do with it. His test in this case can be omitted.
The microswitch, which is sometimes built into the housing, is tested in the same way.
You switch its key and check that there’s a circuit.
These things often break down at high currents. The repair in this case is quite simple. The two wires that are suitable for it are bitten out and connected directly to each other.
The connection place is insulated with a protective cap SIZ or simple duct tape.
The only disadvantage. from now on, the fan heater will work as soon as you plug it in.
When the switch is not equipped, check the following elements of the circuit. By the way, do not forget about the mechanical part.
How to test-call the heating element
Depending on the availability of measuring instruments, the heating element can be checked in one of the following ways. To measure the resistance of the coil and the resistance between the coil and the tube with the help of an arrow tester or multimeter, to test with a phase indicator or an electrician’s tester.
Checking the heating element with an arrow tester or multimeter
To check it, switch on the device in the minimum resistance measurement mode and touch the strips of the tester to the ТEН terminals.
If the coil is open, then an arrow tester will show a resistance of infinity and a multimeter will show “1” instead of the real resistance, which is equivalent to an infinite resistance.
To calculate what resistance should have a coil heating elements depending on its capacity, you can use the online calculator.
It is enough to enter into the calculator windows the voltage for which the heating element is designed and its power. These values are usually stamped on the tube. You can use the information about the power consumption of the appliance. For example, the resistance of the heating element of the electric kettle of 2000 W power is 24.2 Ohm.
If the coil is intact, then you need to touch one end of the multimeter probe to any of the leads of the heating element and the other end to the metal tube. If there is no short circuit between the coil and the tube, then the arrow tester will show infinite resistance, and the multimeter will show “1. If the device will show a different from the specified value, the short circuit is obvious and such a heater can not be further exploited.
Checking the heating element with the LED and the battery or the power supply
If you do not have a tester or multimeter, or died in the multimeter battery type “Crone”, then in the presence of any LED, and they are in almost all household appliances and any battery, even dead, the voltage from 3 V to 12 V, you can successfully test any heating element, including the electric kettle.
In the picture you can see how you can check the integrity of the heating element coil with the help of a dead Krona battery removed from the multimeter (the voltage at its terminals was only 5 V instead of 9 V), a 51 Ohm resistor and a LED. Only need to remember that the LED is not a light bulb and it must be connected according to polarity. Since the heating element itself has a resistance, you can do without the resistor when checking the coil using an old battery.
If the LED is shining, it means that the coil is intact. To check the insulation resistance disconnect the circuit from any of the contact rods of the heating element and touch the tube of the heating element. The LED should not glow.
If there is no battery at hand, it can be successfully replaced by any mains power supply of DC or AC, also fits any charger, such as a cell phone or laptop. In this picture, using alligator clips, the supply voltage is from a DC voltage source. The LED was shining with confidence when the voltage varies from 2.5 to 12 V.
Checking the heating element with a phase indicator
Warning! When checking the heating element with a phase indicator and an electrician’s checker, care should be taken. Touching a live circuit while it is connected to the mains can result in an electric shock. In other words, do not touch the body of the heating element or its terminals with your hand after connecting it to the socket.
If you have an electrician’s phase indicator handy, you can also use it to check if the heating element is working properly. In this case the insulation resistance (between the nichrome spiral and the tube) will be checked with greater certainty, because when you check the multimeter voltage is not more than 9 V, and when you check the indicator more than 220 V.
To check, you must first determine where the phase is in the socket (according to the rules should be on the right) and then connect a piece of wire to the phase terminal of one of the contact rods of the heating element, as shown in the photo.
Then touch the sting of the phase indicator first to the opposite contact rod of the heating element (the indicator light should light up) and then to the tube (the light should not light up).
If when touching the opposite end of the ТEН the indicator light does not shine, it means that the coil is open, and if it shines when touching the tube, it means that there is a breakdown of insulation (the coil touches the tube).
Checking the heating element with the electrician’s control knob
Practically everyone can check the heating element with the electrician’s test cord, because no measuring instruments are required. The essence of the test is to connect in series with the coil of the heating element any bulb, followed by connection of the circuit to the household electrical wiring of 220 V.
To prepare for the test take a plug with a cord and connect one end to any contact pin of the heating element and the other end to the electric socket. Then to the second outlet of the cartridge is connected an additional piece of wire. In the socket screw any bulb, rated for 220V.
First connect the free wire from the socket to the free end of the heating element, as shown in the diagram above. Then plug the plug into the socket. If the coil is working properly, the bulb should shine brightly. If it does not, the coil is broken and you can not check any further, because the heating element cannot be used any longer.