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Amperage of Brake Magnets and Size of Wire Used To Connect 7-Way Trailer Plug To Electric Brakes

Question:

How much much amperage does each electric brake magnet require? I am trying to figure out what size wire to run from the trailer plug to the electric brakes. Thanks

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Expert Reply:

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 on a single axle trailer (2 brakes) would be 6.3 to 6.8 max amps on a 7-inch brake system and 7.5 to 8.2 max amps on 10 and 12-inch brake system. The amps will be higher if using a tandem axle or triple axle trailer.

I am including a link to a FAQ page on Electric Trailer Brake Magnets that will show you how to test them and list the numbers I mentioned above.

On a 7-Way connector the suggested minimum wire gauge for the White (ground) wire, the Red or Black (power) wire, and the Blue (brake power) wire is 12 gauge. The minimum wire gauge for the remaining Green (right turn/brake) wire, the Yellow (left turn/brake) wire, the Brown (tail lights) wire, and the Purple (reverse light) wire is 16 gauge.

expert reply by:
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Jeff D

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Follow up Questions

Jody P.

I just put a brake controller on my Mercedes suv and curious how much current the controls require. Do I need an amplifier/booster or will this drive a two axel brake system?

Etrailer Expert
Reply from Chris R.

You shouldn't need any kind of amplifier for the brake controller - the controller itself should be getting power directly from the vehicle's battery. Are you having any issues with it?

Reply from Akshay S.

@ChrisR Hi, We are developing a semitrailer where brake controller is installed on trailer and getting power from drive unit battery.when detached we need to track trailer so we also place one auxiliary battery in trailer so, that it can power when detached. Can u please suggest how much current will be taken by controller for 12V. Supply. Thank you,

Etrailer Expert
Reply from Jon G.

@AkshayS What size brakes are you dealing with on your semi-trailer? It's my understanding that semi-trailers use air brakes so you'll need to make sure you have some kind of conversion if this is the case. Jeff D addresses 10" and 12" brake assemblies above so if you have something else then that power draw can be different. Just to give you a reference point, the Hopkins Engager Breakaway Battery Kit # 20400 is used for up to 2 axle trailers with electric brakes.

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