How to Test Brake Magnet Amperage on a Trailer with 4 Brakes

Question

Question:

How can I test the unit to see if it is putting enough amps out for a four brake system?

asked by: Jim W

0

Expert Reply:

There are a few different tests that can be done to check the brake magnets individually and as a whole on your trailer. I would first recommend checking the magnets for wear before going on to test for proper amperage. If the magnets show abnormal wear or if you can see the windings beginning to show through the friction surface of the magnet then they will need to be replaced.

Testing the magnets as a whole will involve using a multimeter, that can read up to 20 amps, to test the amperage on the brake output circuit from your brake controller when the trailer is connected to the vehicle. To test with the multimeter, you will connect the ammeter inline with the blue wire (brake output wire) from the brake controller. I have attached a diagram that shows how to perform this test. On a 4 brake system, the maximum amperage draw for 10 and 12 inch brake assemblies should be 15.0 to 16.3 amps and for 7 inch brake assemblies 12.6 to 13.7 amps.

Before you test the brake magnets individually, disconnect the trailer from the tow vehicle. Next, sever the brake magnet wires and connect the ammeter between the positive battery terminal of a separate 12 volt battery or 12 volt independent power source and one of the magnet wires. Then, connect the other magnet wire to the negative battery terminal. For 10 and 12 inch brake assemblies, each magnet should read 3.2 to 4.0 amps at 12 to 13 volts. For 7 inch brake assemblies, the magnet should read 3.0 to 3.2 amps.

If the amperage readings are greater than the specified amounts, replace the magnet(s). If the reading is less than the specified amount, the leads are bad and the magnet(s) should 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 3.0 to 3.8 Ohms for 10 and 12 inch brake assemblies or 3.8 to 4.0 Ohms for 7 inch brake assemblies, then the magnet will need to be replaced.

expert reply by: John H

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Answer 1

You will have continuity between both wire of the brake assembly. You can test the resistance with the Ohmmeter function on your Multimeter #PT89ZR. I have linked an article on testing brake magnets below for you to determine exactly what your ohm…

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Answer 2

You are correct in that a manual override switch will apply the maximum braking power of the trailer brakes, if functioning properly. There are two things you may want to check. The first thing I would do is check to see the trailer brakes are…

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Answer 3

First, do a visual inspection. You should make sure that the front of the magnet is not worn to the point where the interior copper windings are visible. Also, check the armature surface (inside rear of brake drum where magnet rides) is free of…

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Answer 4

On each individual electric brake magnet the amperage draw would be 3.0 to 3.2 max amps at 12 to 13 volts on 7-inch brake magnets and 3.2 to 4.0 max amps at 12 to 13 volts on 10 and 12-inch brake magnets. The max amperage draw for the brake magnets…

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Answer 5

There should only be power entering the brake magnets, not leaving them through the ground wire. I would first start off by regrounding each brake magnets to a new bare metal surface separately of one another and as close to the brake assembly as…

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Answer 6

On a 12 inch brake assembly magnet, you should be getting 3.2 to 4 max amps at 12 to 13 volts. We have an FAQ article that covers testing brakes and brake magnets that should be helpful to you. I have included a link to it. Replacing the magnet is…

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Answer 7

Maximum amperage draw for 4 Brakes that are 10 or 12 inch diameter is 15.0 to 16.3 amps at 12 to 13 volts. The 14 gauge wire may be sufficient but for maximum braking effectiveness at full load capacity. I would opt to run 10 gauge wire. Larger…

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Answer 8

You should be able to ground the brake magnets to the frame of the trailer and have them work fine. Or you can try running a jumper wire back from the ground wire of the magnet back to the main ground of the trailer frame. If you are getting 12…

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Answer 9

The light that indicates that the 12 volt circuit is hot is normal and it will not drain the battery. Think of it as the battery having a really long positive terminal that just extends to the rear of the vehicle. If nothing is drawing power from…

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Answer 10

If the 12-volt pin on your trailer connector isn't working, you've got a missing or blown fuse or the wiring connection at the fuse box under the hood wasn't finalized. You're looking for a 40 amp fuse, located in…

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Answer 11

If your brake controller is set to the maximum output then at the magnets you should be seeing 12 volts. If you get 9 volts then the voltage drop off could be related to the wiring such as loose connections or wire that is too small or too large (we…

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Answer 12

The recommended minimum clearance between gooseneck trailer overhang and truck bed rails is 4-6 inches. I'd recommend 6 inches but a lot of people get by with just 4. Ideally you have at least 6 inches of clearance and the trailer is sitting…

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How to Test Brake Magnet Amperage on a Trailer with 4 Brakes

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