Headlight fluctuation - BMW F800 Riders Forum & Registry



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  1. #1
    Tigcraft's Avatar
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    I’ve just started wearing my new heated jacket and Just noticed today that my headlight at tickover pulses to a similar pace of an indicator lamp when the jacket is switched on. I did a test tonight in the dark and if the jacket is turned off there is no pulsing. This is not when the engine is at higher revs but just on tickover. Also it doesn’t matter what current is drawn from the switch pad on the jacket as it still pulses the same. Any ideas or is it normal?

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  3. #2
    ccramerusc's Avatar
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    Put a voltmeter on it and do the same tests. My bet is that your jacket is drawing more watts than the stator can produce at idle. Our stators put out about 250 watts at idle, peaking at about 400 watts at higher RPM. Unfortunately our bikes use about 150 watts at idle leaving 100 or so to spare. So if your fan, high beam, hand warmers, turn or brake signals are on, then that they increase the usage. My jacket is rated at 70 watts. You can see how you run out of watts quickly.

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  5. #3
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    I agree with Cramer, the issue is likely the relatively weak output of the F800ST electrical system. That is my only complaint about the bike: if a manufacturer (in this case BMW) markets a machine as a sport-TOURER than there should definitely be enough electrical power for heated gear and additional lighting. The only solution is for you to keep the RPM at 4K or higher when using your heated gear. This is not an issue at road speeds, but when toddling around town you must keep the gearbox in a lower gear than you might otherwise use.

    Good luck.
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  7. #4
    Daboo's Avatar
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    The electrical system puts out 400W...which is actually very close to what other bikes produce now. Some of the larger sport-touring bikes though are more in the car-sized electrical output at 700W or more.

    I have a voltage indicator on my GT. It's simple. As long as the light is green, all is good. When the LED turns red...you're pulling from your battery. When I did a check on things last winter, I believe I found I can run my headlights on high beam with aux lights, heated jacket liner and gloves, and heated grips on high while moving. Stop at a traffic light, and the light will turn red. But the answer is simple...just turn the headlights off of high to only low beams.

    My radar detector will tell me the voltage output. It's interesting to watch. I've seen it vary from the low to mid-13 volt output, up to 14.1 volts. My guess, and that's all it is, is the motorcycle's voltage regulator shunts off any electrical output that is not needed.

    I don't understand it all...but I know it works.

    Chris
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  8. #5
    Tigcraft's Avatar
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    Ok then, it is the way it is. I live at the edge of several cities so there’s plenty things to stop for which means dancing on the switches many times per hour. The only thing I didn’t understand was the fact that at tickover with the consumers eating away the power it was ‘pulsing’. I can understand if it just drops down gently and goes laim a bit but why pulse with excitement of power?

  9. #6
    Daboo's Avatar
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    Do you have LED lights?

    I retrofitted LED lights to my Subaru Outback. At idle with the lights in running mode (not full low beam), the lights flicker. I think in that case, it is just a quirk of the LED lights.

    Chris
    Elnathan - 2014 BMW F800GT
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    You could get out the voltmeter as suggested and see if the meter also pulses in time with the lights.

    That may help to differentiate whether the bike is shutting down spark intermittently to the lights specifically, or is just so close to Daboo's code "red" situation above.

    If the volts are low, but stable and lights pulsing: then there is some electrickery going on to conserve spark. BMW engineering high-tech wizardry.
    If the volts are low, but pulsing in time with the lights: then perhaps it is just the regulator/rectifier and alternator shunting the spark from the battery to the frame. Low-tech.

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  12. #8
    RoadRogue's Avatar
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    The pulsing is caused by the temperature controller for your jacket. Because it uses pulse width modulation, the frequency of the pulses will remain constant, but the duration will vary with the temperature you set. The longer the pulses are in the "on" state, the warmer your jacket will be.

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  14. #9
    Tigcraft's Avatar
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    Quote Originally Posted by RoadRogue View Post
    The pulsing is caused by the temperature controller for your jacket. Because it uses pulse width modulation, the frequency of the pulses will remain constant, but the duration will vary with the temperature you set. The longer the pulses are in the "on" state, the warmer your jacket will be.
    That’s interesting, I did a quick check between temperatures of the jacket v pulses and all looked the same no matter what settings. The only difference was the headlight stopped pulsing when the jacket was off

  15. #10
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    Quote Originally Posted by RoadRogue View Post
    The pulsing is caused by the temperature controller for your jacket.
    Nice pick up. That jacket must sure pull some amps.

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    I think RidaMile is correct, electrickery is possibly at play. Tigcraft I don't see where your heated jacket is plugged into, the stock accessory plug on the lower right side of bike or a plug attached to the battery? Possibly what you are seeing is just the BMW canbus system compensating for the wattage draw of your jacket. Since the canbus system doesn't have fused protection for lights and accessories, the canbus controller uses semiconductor switches to isolate any bad/blown devices or shorted wires. Since the headlight is probably drawing the most wattage (plus its' easy to notice)the canbus system may be slightly limiting it's power as the jacket is requesting amperage. It's basically a mini computer doing the function of the old fuse block wiring harness. I'm just assuming, but it could explain it. There might be some thread here on this site or a BMW spec. that talks about running accessories with canbus. Good luck!

  17. #12
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    Quote Originally Posted by XR1000 View Post
    I think RidaMile is correct, electrickery is possibly at play. Tigcraft I don't see where your heated jacket is plugged into, the stock accessory plug on the lower right side of bike or a plug attached to the battery? Possibly what you are seeing is just the BMW canbus system compensating for the wattage draw of your jacket. Since the canbus system doesn't have fused protection for lights and accessories, the canbus controller uses semiconductor switches to isolate any bad/blown devices or shorted wires. Since the headlight is probably drawing the most wattage (plus its' easy to notice)the canbus system may be slightly limiting it's power as the jacket is requesting amperage. It's basically a mini computer doing the function of the old fuse block wiring harness. I'm just assuming, but it could explain it. There might be some thread here on this site or a BMW spec. that talks about running accessories with canbus. Good luck!
    It is the ZFE that controls chassis electrics and the presence of the CANbus has nothing to do with it. This is a common misconception that has been popularized to the point where even vendors get it wrong.

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  19. #13
    guenner's Avatar
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    How is the jacket connected to the bike? Accessory port or wired directly to the battery?

    /Guenther
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  20. #14
    Tigcraft's Avatar
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    I’ve a direct jacket to battery connection so there is no CANbus interference and dictatorship from it.

  21. #15
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    Quote Originally Posted by Tigcraft View Post
    I’ve a direct jacket to battery connection so there is no CANbus interference and dictatorship from it.
    See post #12. Nothing to do with CANbus.

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