Forum Discussion

dclark1946's avatar
dclark1946
Explorer
Oct 22, 2016

Applying Trailer 12V to Trailer Brakes

I use an electric trailer dolly to precision position our TT after pulling it onto our paved parking pad. (We have very limited manuvering room) The dolly has a 7 pin connector cable and a brake control toggle switch that allows you to stop the trailer quickly. The switch is powered by a separate 12V source fed by a cable with small battery clamps.

I have been using a jump start for the 12V source but would like to power the switch from the trailer 12V available on the 7 pin connector. I will also probably add a couple of LEDs to verify 12V power to the switch and 12V power supplied to the brakes. The four brakes pull about 11A when using the jump start but I suspect they will pull more current from the Gr 27 battery. Anyone see any issue with using the trailer battery for short term braking?

5 Replies

  • Lynnmor's avatar
    Lynnmor
    Explorer II
    Oct 23, 2016
    A wire wound resistor is available to reduce braking. A resistor would limit the battery load and reduce magnet heat for extended use. At slow walking pace speeds, there is no need for maximum braking. Resistor
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Oct 22, 2016
    dclark1946 wrote:
    Old-Biscuit wrote:
    No problem

    If you look at end of trailer umbilical cord plug with raised part UP

    11 o'clock is 12V HOT
    7 o'clock is brake controller output

    Make up a momentary spring loaded toggle switch with flat terminals and push them into corresponding pin positions

    Then toggle on/off for braking as needed.

    When On you will have FULL trailer battery voltage so limit amount of on time.
    Otherwise brake magnets could be damaged


    So I sometimes have the brake on for about a minute or so since our pad has some slope. How long can you leave 12V applied before causing damage? I can put a small (0.1 - 0.2 Ohm) power resistor in series to limit current.


    That minute or so is not an issue
    An hour or more could be...... (Fed DOT requirement is full voltage for 15 minutes via emergency brake away switch)

    That is why I suggested spring loaded momentary toggle switch so that it can't be LEFT on
  • dclark1946's avatar
    dclark1946
    Explorer
    Oct 22, 2016
    Old-Biscuit wrote:
    No problem

    If you look at end of trailer umbilical cord plug with raised part UP

    11 o'clock is 12V HOT
    7 o'clock is brake controller output

    Make up a momentary spring loaded toggle switch with flat terminals and push them into corresponding pin positions

    Then toggle on/off for braking as needed.

    When On you will have FULL trailer battery voltage so limit amount of on time.
    Otherwise brake magnets could be damaged


    So I sometimes have the brake on for about a minute or so since our pad has some slope. How long can you leave 12V applied before causing damage? I can put a small (0.1 - 0.2 Ohm) power resistor in series to limit current.
  • Old-Biscuit's avatar
    Old-Biscuit
    Explorer III
    Oct 22, 2016
    No problem

    If you look at end of trailer umbilical cord plug with raised part UP

    11 o'clock is 12V HOT
    7 o'clock is brake controller output

    Make up a momentary spring loaded toggle switch with flat terminals and push them into corresponding pin positions

    Then toggle on/off for braking as needed.

    When On you will have FULL trailer battery voltage so limit amount of on time.
    Otherwise brake magnets could be damaged

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