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Thread: Power from the BMW accessory port - 12v/5A or only what my device draws?

  1. #1

    Power from the BMW accessory port - 12v/5A or only what my device draws?

    Good Saturday all!

    I am mounting a Valentine 1 radar detector on my 2019 R 1250, Valentine supplies a standard wiring harness that I can easily attach directly to a 12v DIN plug that I have, that will of course plug in to the standard BMW accessory port, (no power controller used currently, just the factory accessory port alone)

    the Valentine harness has a 2A fuse in the live circuit (red wire) and I believe that the BMW accessory port supplies 12v up to the fused maximum of 5A . . . is it 5A?

    so I have some questions that anyone with moderate knowledge of electric circuitry will find pretty dumb . . . but . . .

    1) when a bike supplies an accessory power port with a spec of, say, 12v and 5A - does this mean that that port will literally "push" 5A into whatever you plug into it, all the time? I'm sure that's not true. What I think it means is that it's all based on "draw" - whatever device you plug into the accessory port will simply draw what it needs, and if that's more than 5A, then the port's circuit fuse will blow and there you go. The accessory port is based on draw, am I right?

    2) therefore, for the radar detector itself, with its 2A circuit in the power harness, this means that the detector will draw, say, 1.5A at 12v for operation, and the 2A fuse is there in the circuit so that if the bike's electrical system has a power surge and does (rarely, I hope) try to push out a 7A current spike, the radar detector's power line will blow its 2A fuse and the detector isn't harmed. Is that correct?

    3) IS the BMW accessory port offering up to 5A? or am I off there?

    Therefore, I can safely wire up my power supply for the radar detector and plug that assembly into the accessory port and that is what the engineers at BMW and Valentine intended?

    4) Lastly, in wiring the DIN plug, I expect that I'd connect the red wire of the Valentine harness (with its 2A fuse inline) to the central power connector on the DIN plug, and the black wire of the Valentine harness to the outer, cylindrical connector of the DIN plug, is that correct? The DIN plug that I'm using had a different cable attached to it before I disassembled it, and I noted carefully that that's how it was wired then - red to centre, black to outer. I assume that the black wire goes to a frame negative/ground, sort of thing?


    I have attached a photo of the DIN plug and the Valentine wiring harness so folks who know this stuff can see exactly what I'm doing. The Valentine harness technically ends in an RJ11 socket, and the Valentine RD plugs into that, not directly into the BMW accessory port, but that's a non-issue I suspect.

    Aside from my somewhat lame questions (the detector is about $700 to a Canadian, so, you know . . . ), does anyone have any other points about mistakes not to make?

    thanks in advance to some wonderful owners, I can't believe how excellent it is to have you folks out there!

    Peter in BC

    Tiny Valentine.jpg
    Peter Brassel
    Life's roads are full of lumps and bumps . . . ride a GS!
    2019 R1250 GS Adv.

  2. #2
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    It will only draw what it needs. If it's 2 amps thats all it will draw from the accessory port. On the other hand, if you were to install something that needed more amperage than the port is rated for (some heated gear for example) you'd blow the inline fuze or the can bus would shut off power to the aux. port. That's my rudimentary understanding of it. I'm sure someone with a degree in electrical engineering will come on to elaborate.

  3. #3
    SURVIVOR akbeemer's Avatar
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    Quote Originally Posted by motormike View Post
    It will only draw what it needs. If it's 2 amps thats all it will draw from the accessory port. On the other hand, if you were to install something that needed more amperage than the port is rated for (some heated gear for example) you'd blow the inline fuze or the can bus would shut off power to the aux. port. That's my rudimentary understanding of it. I'm sure someone with a degree in electrical engineering will come on to elaborate.
    Mike is correct. There is one other thing to consider. The auxiliary power outlet will be continued to be powered after the ignition is switched off for a set duration.... I cannot recall how long the power lasts, but for a minute or less. If you are invited to a roadside chat with a LEO, then it may be considered bad form to have the V1 squawking during the conversation. Best practice an emergency shutdown procedure.
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    The fuse in the V1 power lead is there to protect you and the bike from a fire should the power lead come in contact with ground - such a connection would attempt to draw more current than the wiring can handle, thus melting the wires.

    The rest of your assumptions are correct, the outlet will only allow you to draw up to 5 amps before the CAN-BUS system will cut power. The bike doesn't "push" 5 amps all the time, it allows current flow up to 5 amps then cuts the current flow off. For instance, when nothing is plugged into the socket, there is no current flow at all.
    Don in Pahrump, NV
    2006 BMW R1200RT

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    Quote Originally Posted by djdixon View Post
    The rest of your assumptions are correct, the outlet will only allow you to draw up to 5 amps before the CAN-BUS system will cut power.
    The CAN-bus does not cut power. The CAN-bus is a controller area network facilitating data communications amongst the bike's various controllers. Chassis electrics are controlled by the ZFE.

  6. #6
    Registered User Guenther's Avatar
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    Tiny Valentine.jpg

    In case you do something wrong, the inline fuse protects the radar detector and the electronic fuse of the ZFE computer protects the wire to the motorcycle's electric.

    If the ZFE detects a draw of more than 5A - typically a short - it shuts down the power for this output. Every time the bike is started the ZFE starts checking the power line. If the overdraft has been fixed then 12V power is applied again.

    ZFE computer = Zentrale Fahrgestell Elektrik = Central Frame or Chassis Electric

    /Guenther
    2017 F700GS - I wish she had a drive shaft

  7. #7
    Quote Originally Posted by Guenther View Post
    Tiny Valentine.jpg

    In case you do something wrong, the inline fuse protects the radar detector and the electronic fuse of the ZFE computer protects the wire to the motorcycle's electric.

    If the ZFE detects a draw of more than 5A - typically a short - it shuts down the power for this output. Every time the bike is started the ZFE starts checking the power line. If the overdraft has been fixed then 12V power is applied again.

    ZFE computer = Zentrale Fahrgestell Elektrik = Central Frame or Chassis Electric

    /Guenther
    Thanks Guenther,

    and by adding the "positive" note and arrows to my photo, you are confirming that the red wire should be connected to the central post, black goes to the connector for the outer ring. Correct?
    Peter Brassel
    Life's roads are full of lumps and bumps . . . ride a GS!
    2019 R1250 GS Adv.

  8. #8
    Fortis Fortuna Adiuvat Omega Man's Avatar
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    This comes up fairly regularly. Along with the confuzlement on Can Bus/ZFE. Direct to a lead on the battery usually solves the confusion. A fused SAE connector will enable Batter Tender access and radar detector power.
    If more 12V power is needed, a Fuze Block or similar accessory could be the next step.
    Good luck.
    OM
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    Registered User drneo66's Avatar
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    Quote Originally Posted by pmariana View Post
    Thanks Guenther,

    and by adding the "positive" note and arrows to my photo, you are confirming that the red wire should be connected to the central post, black goes to the connector for the outer ring. Correct?
    Correct - positive (generally red for those reading this in the future) to the center post. Negative (black) to the outer ring. Wire bent in a shepherd's staff, wrapped clockwise so as you screw it down, the screw draws in the wiring.
    Current: 2007 BMW R1200RT, 2013 F800GS
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  10. #10
    Debbie's Servant Lee's Avatar
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    Quote Originally Posted by RadioFlyer View Post
    The CAN-bus does not cut power. The CAN-bus is a controller area network facilitating data communications amongst the bike's various controllers. Chassis electrics are controlled by the ZFE.
    I could understand djdixon's reply
    Lee
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  11. #11
    Quote Originally Posted by drneo66 View Post
    Correct - positive (generally red for those reading this in the future) to the center post. Negative (black) to the outer ring. Wire bent in a shepherd's staff, wrapped clockwise so as you screw it down, the screw draws in the wiring.
    Thanks drneo66, I also appreciate the “proper workmanship" note of bending the wire insert and how to orient its insertion to match the screw’s rotation,

    My 50’s British Dad would have so instructed too . . .

    Peter Brassel
    Life's roads are full of lumps and bumps . . . ride a GS!
    2019 R1250 GS Adv.

  12. #12
    Registered User drneo66's Avatar
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    Quote Originally Posted by pmariana View Post
    Thanks drneo66, I also appreciate the “proper workmanship" note of bending the wire insert and how to orient its insertion to match the screw’s rotation,

    My 50’s British Dad would have so instructed too . . .

    Every day someone is born who doesn't know how to properly tighten a wire under a screw
    Current: 2007 BMW R1200RT, 2013 F800GS
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