Dimming 12GS lights.

[Chris Terry]

Last night comming back from Poole (great meet!) I noticed that the headlight on my 12GS dims when I apply the brakes. I suppose the extra load from the brake light is causing it. Has anybody else noticed this on their bike?.

 

[Allroad]

cant say that i have

 

[peterh]

I have ....

 

[Dave Price]

Yes, I noticed it from day one, and like you posted the fact.
However, never caused a problem in 10K miles. It's probably the amount of current being taken by the brake servos?

 

[nadeem]

all the servo-assist bikes do it, more noticeable when at tickover - the servos use a lot of power...

 

[Chris Terry]

OK so it's not just my bike that has the problem. Now... is it a fault or feature??. Well it looks to me like a design fault. Of all the bikes I have owned the BMW is the only one that has this problem. Looks like the cabling is not up to the job.

 

[Gonzo]

OK so it's not just my bike that has the problem. Now... is it a fault or feature??. Well it looks to me like a design fault. Of all the bikes I have owned the BMW is the only one that has problem. Looks like the cabling is not up to the job.

Yeah, but how many other non-BMW bikes that you've owned have electric brake servos?

Analogy - next time you're in the car in the dark with the headlights on at tickover, switch on the aircon or try and wind the electric windows up when they're already closed. The same sort of thing happens, momentarily. (Well it does in mine but then it's not exactly the best car in the world).

 

[Chris Terry]

My point is that any manufacturer who intends to build better products needs to ensure that all the fitted components work as a complete system.
...Or you might get the situation where you can only have non-dimming lights on the non-servo model!. And my car lights stay bright when I brake at speed.

 

[Mouse]

Cars' electrical systems have an easier time of it, because they have physically larger batteries with a lower internal resistance, and probably larger alternators. I too get a momentary dimming of the headlight when using the brakes, can't say I really rate it as a problem though.

 

[stephenm]

My point is that any manufacturer who intends to build better products needs to ensure that all the fitted components work as a complete system.
...Or you might get the situation where you can only have non-dimming lights on the non-servo model!. And my car lights stay bright when I brake at speed.

The brake servo motor is drawing enough current to momentarily drop the battery voltage slightly. You see this as as a slight dimming in the headlight. It's transient, expected and harmless. Whether you notice it or not, it happens on all bikes and cars when the electrical load increases. It happens in your house when you put the kettle on.

Stephen

 

[ClearwaterBMW]

well-said, stephen,
it IS normal
bmw does a better job of this than most

i remember my old harley.... years ago
at idle
at a light
even with the brakes off.... the lights would dim a lot just from the decreased alternator output at low engine speed

there's only so much a bike can do in the way of putting out power
what they need to do is invent headlights that:
- put out the exact same light output from 10-15 volts
now THAT would solve you perceived problem

greg

 

[Deleted account 211025001]

Can't say I find it a problem at all.

I've had several bikes over the years that would dim and brighten the head light in time with the indicators!

Andres

 

[Chris Terry]

Hang on guys; I still stand by what I said…… “dims when I apply the brakes”
And stays dim until the brakes are released. NOT momentary dims (while the alternator\regulator reacts), or dims at at tick over!
I mean travelling along with the engine running at 3000+ rpm.

 

[Dave Price]

Hang on guys; I still stand by what I said…… “dims when I apply the brakes”
And stays dim until the brakes are released. NOT momentary dims (while the alternator\regulator reacts), or dims at at tick over!
I mean travelling along with the engine running at 3000+ rpm.

yes, mine's the same. Although I put up with the phenomenon, I've never experienced it with other electrical systems, except at tickover, when the alternator output is low.

 

[Chris Terry]

I don't think it's a phenomenon Dave P, I suspect the design, under rated cables for example. I'll take some measurements of voltages just to see, but I recon the battery terminal voltage will remain constant while the headlamp connection voltage will not.

 

[Chris Terry]

Sorry guys! ter I just checked my GS and the dimming of the lights only happens for a moment as the brake is applied and returns back to full brightness within a second or so. I am happy again now but a bit embarrassed to have set you off on the wrong track :goof :goof jerkit