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How to Use a Multimeter to Test Electronic Relays?

Author: William
Date: 10 Dec 2022
how to test a 5 Pin relay with a Multimeter

Overview of Relay

Video related to test a relay

Overview of Multimeter

What can be a relay used for?

Some matters related to relay need attention

How To Test a Relay?

Elementary course of testing a relay

Solid-State Relay Testing

Coil Relays Testing

How Can a Relay Be Tested Using a DC Power Supply?

How to detect a bad relay?

How to test a 5 Pin relay with a Multimeter

How to Test a Car Relay?

Relay FAQ


Overview of Relay

An electromagnetic switch is essentially what a relay is. A coil, an armature, and a few contacts make up the device. The armature is drawn toward the coil when a low voltage (and low current) signal is sent across it, turning the coil into an electromagnet. The armature as a result changes from one contact to the other. The coil de-energizes and ceases to function as an electromagnet when the voltage applied across it is removed. Back at the other contact, the armature flips.

Normally Open (NO) and Normally Closed (NC) are the names of the connections (NC). The armature makes contact with the Normally Closed (NC) contact when the electromagnet is inactive (the coil is de-energized). The armature comes into contact with the Normally Open (NO) contact when the electromagnet is in operation (the coil is energized). The armature is referred to as COM because it serves as the common point for both NO and NC connections (short for Common).

The COM terminals alternate between switching to NO or NC depending on whether the coil is energized, whereas the NO and NC terminals are also independent of the coil.



Video Description: This video shows you how an automotive relay works and how you can test it using an digital multimeter. This is the easiest way to do it out of the car and the only way it should be done.



Overview of Multimeter

A measurement device that can assess several electrical characteristics is a multimeter. The term "volt-ohm-milliammeter" (VOM), which refers to a multimeter that has the ability to measure voltage, resistance, and current, is also used to refer to a normal multimeter that is capable of doing so. Some include the measuring of other characteristics like capacitance and temperature.

Readings are displayed on an analog multimeter's microammeter, which has a moving pointer. Because they are more affordable, accurate, and physically robust than analog multimeters, digital multimeters (DMM, DVOM) with numeric displays have all but replaced analog multimeters.


What can be a relay used for?

Relays are utilized in almost every type of vehicle, including marine and aircraft ones. They are typically employed to enable the control of larger amperage circuits by low amperage circuits. Relays serve as switches that enable the low amperage circuit to turn on or off the high amperage circuit. As an illustration, consider the headlights of your car. The amperage could surpass the switch's capacity if you attached the lights directly to it, which could lead to cables melting and even even a fire in some circumstances. Relays can also manage many systems simultaneously, such as turning on the headlights in conjunction with the radio or extending the antenna in conjunction with the windshield wipers.


Although relay testing is an easy process, safety should always come first. When using relays, it's a good idea to keep the following in mind:

  • Even if you're a seasoned garage tinker, use the service manual—not the owner's manual—to identify and comprehend the wiring system and relays in your car.
  • Never begin working with relays or anything electrical in an area that has fuels or other flammable or explosive gases present.
  • The relay should be handled carefully to prevent dropping it. If the relay has an internal problem, the wiring may burn or melt. Do not alter the relay in any way, either.
  • Relays from other areas of the car or from a random junk bin in your garage should not be mixed together if you've decided that the relay is broken and has to be replaced. The electrical system of your car could be harmed by a power surge or short due to a bad relay.


How To Test a Relay?

Relays are crucial electronic components that allow low-powered devices like microcontrollers to operate high-powered ones, as is evident from the explanation above. Relays are mechanical devices, and as they can develop faults over time, it is crucial to examine whether they are functioning properly. If it stops working, a new one needs to be installed right away.

How then do you test a relay? There are various methods for determining whether a relay is operating as intended or not. We will explore a few different ways to test relays, and more importantly, we will learn how to use a multimeter to test relays.


Elementary course of testing a relay


Step One: Do a preliminary visual assessment of the relay

Many relays have a clear plastic shell containing the coil and contacts. Visible damage (melting, blackening, etc) will help narrow down the issue. Most modern relays have an LED to tell you if they are in the active state (ON). If that light is off and you've got control voltage to the relay or coil terminals then you can safely assume that relay is bad.

Visual inspection of the relay


Step Two: Cut off the power source

Including batteries and line voltage, all power sources should be turned off before performing any electrical work. The circuit's capacitors should receive extra attention since they have a long hold-on period after the power source is turned off. Avoid discharging capacitors by shorting their terminals. Before doing any electrical repair, it is advisable to check your local rules; if you feel dangerous, leave it to the experts. Extra low voltage work normally will not fall under this criteria, but it's still necessary to remain careful.

Cut off the power source


Step Three: Consult the datasheet or relay schematic

Relays have fairly common pin configurations, however it is best to look up the data sheets of the manufacturer, if any, to learn more about the number of pins. These are usually printed on the relay.

Datasheets occasionally provide information on pin configurations, current and voltage ratings, and other details that are invaluable for testing and help to reduce testing errors to a minimum. It is feasible to test pins arbitrarily without knowing their configuration, although results could be unpredictable if the relay is damaged. This information may also be printed directly on the body of some relays, depending on their size.

Relay schematic


Solid-State Relay Testing


Step One: Use an multimeter to check solid-state relays

Solid-state relays almost invariably fail when they begin to short. When the control power is turned off, solid-state relays should be tested using an ohmmeter across the normally open (N.O.) terminals. When control power is applied, the relays should be open, switched to OL, and then closed.

Use an multimeter to check solid-state relays


Step Two: Use a multi-meter in diode-test mode

By taking a multimeter, switching it to the diode test mode, and checking between A1(+) and A2, you may further prove that the relay is defective (-). To cause the semiconductor to conduct, the meter will apply a little voltage, and the screen will display the voltage. This will inspect the transistor (usually an NPN) from its base (P) to its emitter. When the relay is functioning properly, the meter will read 0.7 for a silicon transistor (which almost all of them are) or 0.5 for a germanium transistor rather than 0 or OL when it is defective (which are relatively rare but not unheard of).

Use a multi-meter in diode-test mode


Step Three: Keep SSRs at an appropriate temperature

When kept cold, solid-state relays are simple to repair, inexpensive to replace, and have a long lifespan. New relays typically come with block mountings and DIN rail bundles. Another unique sort of relay known as an SCR is available in two flavors for heating wires, IR lamps, and ovens, typically for fine-tuning process temperature. This switch can turn on and off and is essentially a fast switch on a much quicker switch, which frequently fails as a result of temperature changes.


Coil Relays Testing


Step One: Identify the relay's required coil specifications

The relay case ought to bear the part number of the manufacturer. Find the voltage and current demands for the control coil on the relevant data sheet. Larger relays may additionally have this printed on the casing.


Step Two: Check to see if the control coil has a diode

To prevent the logic circuitry from being harmed by noise spikes, the pole is frequently surrounded by a diode. Drawings of the diode will depict it as a triangle with a bar spanning one of its corners. The input, or positive connection, of the control coil will be where the bar will be linked.

Diode protection


Step Three: Examine the relay's contact setup

This can be found on the data sheet provided by the manufacturer or even printed on the case of larger relays. Relays may have a single pole or multiple poles, which are represented in drawings by a single line switch coupled to a relay pin. A normally open (NO) or normally closed (NC) contact may be included on each pole. These contacts will be shown on the drawings as pin connections on the relay. Each pole will either be touching the pin on the relay drawings, indicating an NC contact, or it will not be touching the pin, indicating a NO contact.

Relay Terminals


Step Four: Check whether the relay contacts are deactivated

Test the resistance between each relay pole and the matching NC and NO contacts by using a digital multimeter (DMM). To the appropriate pole, all NC connections should register 0 ohms. To the appropriate pole, the NO connections should all report infinite resistance.

Test the de-energized condition of the relay contacts


Step Five: Power the relay

Use an independent voltage supply appropriate for the rating of the relay coil. If the relay coil is diode protected, be sure that the independent voltage source is connected with the right polarity. When the relay is activated, keep an eye out for a click.

Power the relay


Step Six: Verify that the relay contacts are powered on

Test the resistance between each relay pole and the matching NC and NO contacts by using a digital multimeter (DMM). To the matching pole, the NC connections should all register infinite resistance. The resistance for each NO contact should be zero to the associated pole.


How Can a Relay Be Tested Using a DC Power Supply?

In the first approach, we'll just turn on and off the relay's coil to determine if the armature switches between the two ends. Assuming a 12V relay, use a switch to connect the coil terminals to a battery or a 12V DC power supply. When the switch is closed, the circuit is finished and the coil is turned on. The armature should switch to a normally open contact as a result. The armature ought to return to the Normally Closed contact if we flip the switch open. This is an easy way to test relays, especially automobile relays because a 12V battery is so accessible.


How to detect a bad relay?

A multimeter is the sole tool needed to test a relay. Check to determine whether there are 12 volts at the 85 position in the fuse box where the relay plugs in with the relay removed from the fuse box, the multimeter configured to measure DC voltage, and the switch in the cab turned on (or wherever the relay is located). Check to see whether the relevant fuse has blown if there isn't one there. Make sure the switch is allowing current to flow to the relay if the fuse is in good condition. Once you are certain that there is voltage at slot 85, switch the multimeter to continuity mode and check to see if there is a solid ground connection at slot 86. Once you've established that voltage can pass through that side of the relay, check the 87 connection point to see whether battery voltage is present. If not, this could possibly point to a blown fuse or circuit breaker.

How to detect a bad relay


To confirm that there is a solid connection between the relay and the component, use the multimeter's continuity function once more. The 30 terminal should have one lead and the component's positive voltage connection point should have the other. Depending on how distant the component is from the fuse box, you might need to attach the multimeter lead to an extension to reach it. If everything is in order, the relay is likely to be at fault. To double-check that and be certain, it is simple to do so. Simply insert a cotter pin or wire between the 87 and 30 connection points on the relay in the fuse box. The component ought to start operating. This is a quick and effective emergency fix that will let you return the machine to the yard until the relay can be changed. A fuse will still be present to protect the circuit because a relay is not a fuse.


How to test a 5 Pin relay with a Multimeter

Relays, which are used to regulate the power supply to a circuit or piece of machinery, are essentially electrical switching devices. We cannot solely rely on direct power supplies to manage systems with severe loads. However, we are able to control this with the aid of a system that can switch, postpone, or stop the flow of power. Follow these easy instructions below to check the malfunctioning 5-pin relay.

5 pin relay

  • Every relay typically has three fundamental terminals: ordinarily open (NO), usually closed (NC), and common, in addition to its power terminal.
  • Check the relay physically first; it shouldn't show any symptoms of wear, sparking, or debris. If not, it would be wiser to replace it.
  • Now, turn on the relay's power source, which might be 12 volts direct current (DC) or 220 volts direct current (AC), and check the voltage value coming into the relay with the use of a multimeter. This has proven that the relay does not have a power problem.
  • Change the resistance testing point on your multimeter to the highest ohms range.
  • Place a meter probe on the usually open (COM) point of the relay and the other on the normally closed (NC) point. If the relay is functioning properly, this terminal should register zero or very near to zero ohms.
  • Now join the automobile meter's COM terminal to one probe and the NO terminal to the other.
  • This point of relay is functioning accurately if the meter reads milli ohms or even higher ohm values. If the findings are close to 0 ohms, this is unquestionably a defective relay, and you need to replace it right away.
  • We have so far verified the relay's NO and NC terminals; if there are no issues with these locations, we should inspect the coil.
  • Connect multimeter probes to the terminals of the relay to measure resistance. Read the handbook or guidebook for particular relay to confirm the rated value of resistance for the relay coil.
  • If you have an Ehdis 5 pin relay with model number JD2912-1Z, your ohm value should be close to 80 ohms. The relay coil is not functioning properly if the meter result is noticeably higher or lower than this range.


How to Test a Car Relay?


Step 1: Supplies Required to Test a Relay

Test light, Ohmmeter, Vehicle service manual, Replacement relay, and Jumper wires are all needed to test a car relay. Before you begin, arrange all of your supplies for the greatest outcomes. To avoid having to leave what you are working on, you want everything to be within arm's reach.


Step 2: Locate the Relay

You must locate the relay before you can test it. Relays can be found in a variety of places, including the engine compartment and beneath the dash.

Depending on what the relay controls, the position will change. If you're not sure where it is, check the wiring diagram in your car's service manual.

Locate the Relay


Step 3: Exchange the relay

Swapping the relay with a working one is the simplest approach to test it. However, by doing this, you run the danger of damaging a reliable relay due to an electrical short or other issue. Additionally, this process can result in you spending more money than is necessary. If you choose to follow this path, be sure to inspect and clean the connectors while the relay is out of the way.


Step 4: Use a Multimeter on automobile to test relay

You could examine the relay using your multimeter. To measure resistance, set the multimeter to Ohms and connect the leads across the input and output pins. Most relays should have a resistance between 50 and 120 ohms.

If the multimeter displays Open or Out of Range, a faulty coil winding may be the cause. You require a replacement relay in this situation. You can connect the leads between the switch pins if everything appears to be in order. Relays that are open will display OL or Open.

Use a Multimeter


Step 5: Energize the relay

The relay should then be powered by a 12-volt battery. The relay coil should close the connection with a clicking sound. Diode relays require proper polarity, although 4-pin relays do not. Connect your test light to the switch terminal and the ground. If everything is running smoothly, your test light will detect the current and turn on. The light ought to turn off when you take the jumper out.


Step 6: Switch Testing

Moving on to the switch is what you want to do if everything is working as it should. A poor contact point can cause voltage to decrease or to be completely absent. Put the test light out of the way and switch your multimeter to read DC. The switch pins' leads should be connected. This measurement ought to reflect the same voltage as your battery, which is normally 12V.

Next, check the switch's resistance. The jumper needs to be removed before you turn on the relay. The multimeter should be set to measure ohms, which is the switch's resistance. The closed relay will be OL or Open, however the activated open relay will measure almost 0 ohms.

After completing these steps, if you are still unable to diagnose the relay, expert assistance may be required.


Relay FAQ

Can I Test Relays Without a Test Light or an Ohmmeter?

No. You have two options if you're sure there's a relay issue but lack the testing equipment. The simplest course of action is to be cautious and simply replace the relay, but you may also hire a mechanic to test and repair the relays for you.


What Happens If the Relays on My Vehicle Are Hiding or Difficult to Find?

The majority of relays ought should be situated in accessible areas, but if there is one about which you are unclear, it is advisable to have a specialist inspect it. Blindly rummaging around under your hood can ruin good relays and cause serious knuckle damage.


How Much Does It Cost To Test A Relay?

The relay itself is the most expensive component of testing and replacing relays in your car. A relay can cost anything from $5 to several hundred dollars, depending on what it is controlling.

Ohmmeters come in a number of styles and may be obtained for less than $20. The typical price range for high-impedance test lights is between $20 to $40, although investing more money doesn't always result in a better product. Last but not least, jumper wires are affordable, with prices ranging from $2 to more than $50, depending on the length of the cable.


What is difference between relay and switch?

You are accurate in saying that a relay is essentially simply a switch, however it is a switch that can be controlled remotely. A standard switch regulates electrical current by establishing or destroying the path of either the positive (the most prevalent) or the negative (less common) side of a circuit.


How to test a DC relay with a multimeter?

Take the multimeter's leads and place them across the relay's coil terminals. The multimeter should display a reading of between 40 and 120 for a typical coil. The meter will display out of range if the coil is damaged, or if it is open, in which case you must replace the relay.

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