Trystan Casey
Electric trailer brake magnets should be inspected and tested each time the brakes are worked on. There are several ways to test the amperage of the magnets. One way is to use a magnetic compass to verify that the magnets are actuating when you apply the brakes. Another way is to use a multimeter that reads amps and ohms. If there is any visible sign of wear on the magnets, such as exposed windings, or if there is any grease or oil residue, the magnets will need to be replaced.
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What You'll Learn
Check for abnormal wear and exposed windings
Before testing the magnets with a meter, check for any signs of abnormal wear. If the windings are beginning to show through the friction surface of the magnet, they will need to be replaced. This is because, once the copper becomes exposed, it can cause an open electric circuit and render your brakes useless.
You can also check the four small holes on the face of the magnet (the side that is in contact with the brake drum). These are known as "wear indicators". If you cannot see the wear indicator holes, or if there are fewer than four, you need to replace the magnet. If the centre of the magnet hole has worn, you need to replace the magnet and may need to replace the lever.
Magnets can also fail without showing visible signs of wear. If you suspect your magnets are faulty, you can test them with an ammeter. First, make sure the trailer is not connected, as you run the risk of shorting out the brake controller or other electrical components. Then, connect the ammeter between the positive battery terminal of a separate battery and one of the magnet wires. After that, connect the other magnet wire to the negative battery terminal. If the amperage is greater than the specified amount, replace the magnet. If the reading is less than the specified amount, the leads are bad and the magnet should be replaced.
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Test with a meter or ammeter
To test electric trailer brake magnets with a meter or ammeter, you will need a multimeter that reads amps and ohms. A good brake controller, like the Tekonsha P3, has test functions built-in.
First, ensure the trailer is not connected to the vehicle when performing the test. If the trailer is connected, you run the risk of shorting out the brake controller or other electrical components.
To test the brake magnets with an ammeter, connect the ammeter between the positive terminal of a separate 12-volt battery and one of the magnet wires. It does not matter which magnet wire you choose. Then, connect the other magnet wire to the negative battery terminal.
Check the amperage. If the amperage is greater than the specified amount, replace the magnet. If the reading is less than the specified amount, the leads are bad, and the magnet should be replaced.
You can also use an ohmmeter to check the resistance between the brake magnet wires. If the resistance is not within the specified range, the magnet will need to be replaced. For example, a 7-inch brake magnet resistance should be 3.8-4.0 Ohms, while 10 and 12-inch brake magnets should be 3.2-3.5 Ohms.
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Check amperage and ohms
To check the amperage and ohms of electric trailer brake magnets, you will need a multimeter that reads amps and ohms. A good brake controller, such as the Tekonsha P3, has test functions built-in.
Firstly, you will need to test the individual brake magnets for proper amperage. To do this, connect the ammeter in line with the blue wire exiting the back of the brake controller or use the brake controller's diagnostic readings. Check the amperage. If the amperage is greater than the specified amount, replace the magnet or magnets. If the reading is less than the specified amount, the leads are bad and the magnet or magnets should be replaced.
To determine if a brake magnet has an internal short, touch the base of the brake magnet to the negative post of a 12-volt battery. Then, connect one of the brake magnet wires to the negative lead of a multimeter and the positive lead of the multimeter to the positive post of the battery. If any amperage is detected, the magnet is shorted and will need to be replaced.
Further testing can be done with an ohmmeter. Using the ohmmeter function on the multimeter, check the resistance between the brake magnet wires. If the resistance is not within the specified range, then the magnet will need to be replaced. For example, the resistance for a 7-inch brake magnet should be 3.8-4.0 Ohms, while for 10 and 12-inch brake magnets, it should be 3.2-3.5 Ohms.
It is also possible to check for a completely failed magnet by visually inspecting the magnets for wear and tear. If any coil can be seen on the centre of the magnet, or if there is abnormal wear and tear, the magnet is likely worn out and should be replaced.
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Inspect for grease or oil residue
Before inspecting electric trailer brake magnets for grease or oil residue, it is important to check the magnets for any signs of abnormal wear and tear. If the windings are visible through the friction surface of the magnet, this indicates that the magnet needs to be replaced.
To inspect for grease or oil residue, begin by disconnecting the trailer from any power source to avoid shorting out the brake controller or other electrical components. This is a crucial safety step. Next, carefully examine the surface of the magnets, paying close attention to any signs of grease or oil buildup. Grease or oil residue on the magnets can interfere with their proper functioning and may indicate a leak or contamination issue.
Use a clean, dry cloth to wipe down the magnets gently. If you notice any areas of grease or oil buildup, pay close attention to those areas and ensure they are thoroughly cleaned. It is important to use a non-abrasive cloth to avoid damaging the surface of the magnets.
If, during your inspection, you notice that the windings are visible or that there are other signs of advanced wear, it is advisable to consult a professional for further guidance. In some cases, the magnets may need to be replaced entirely to ensure the safe operation of the trailer brakes.
By regularly inspecting electric trailer brake magnets for grease or oil residue and addressing any issues promptly, you can help maintain the proper functioning of the trailer brake system and ensure safer towing. Remember to consult a qualified technician if you have any concerns or if the problem persists.
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Use a magnetic compass to verify magnets are actuating
When activating a trailer brake system, current flows from its controller through wires to magnets that slide towards a drum and trigger an inner actuating arm to rotate, pushing against brake shoes to slow the trailer down. If the magnets aren't performing as intended, this could indicate that current is not reaching them, which could be due to wiring issues or a defective controller.
To check if your trailer brake magnets are actuating, you can use a magnetic compass. Here's a step-by-step guide:
- Set a compass near the bottom of your wheel, between the spokes, so it's close to the brake drum. Take note of the direction of the compass needle.
- Pull the breakaway pin.
- Observe the compass needle. If the needle deflects, it indicates that the magnets are actuating. If there is no deflection, it suggests that the magnets may not be engaging, and further troubleshooting is required.
- Replace the breakaway pin.
- Repeat the above steps for each wheel.
It's important to note that the needle may not point directly towards the magnet due to the broad magnetic field that is set up. This method verifies that the magnets are working, but it does not indicate whether the brakes are adjusted properly.
Additionally, you can also use a multimeter to test trailer brake magnets. A multimeter can measure resistance, voltage, and amperage. By connecting the probes of the multimeter to the appropriate wires, you can determine if the magnets are receiving the correct voltage and current. If the readings are outside the specified range, it may indicate issues with the magnets, wiring, or controller.
Other methods for checking electric trailer brake magnets include visual inspections for abnormal wear and tear, checking for exposed windings, and verifying the functionality of the brake system as a whole.
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Frequently asked questions
Check the magnets for abnormal wear. If the windings are beginning to show through the friction surface of the magnet, they will need to be replaced.
First, ensure the trailer is disconnected. Then, use an ammeter to test the amperage. Connect the ammeter between the positive battery terminal of a separate battery and one of the magnet wires. Then, connect the other magnet wire to the negative battery terminal. If the amperage is greater than the specified amount, replace the magnet. If the reading is less than the specified amount, the leads are bad and the magnet should be replaced.
You can use a magnetic compass to verify that the magnets are actuating when you apply the brakes. Set a compass near the bottom of your wheel between the spokes, close to the brake drum. Then, pull the break-away pin and verify that the needle on the compass deflects.
If you can see any coil on the centre of the magnet, the magnet is worn out and should be replaced. If there is grease or oil residue on the magnet, it should also be replaced.
