Low battery light comes on even after service???

[Sebretian]

I took the bike in for it's 10,000 km (6000 mile) tune up and had them check out why the low bat charge light would come on for about 5 seconds after starting. Also get an annoying chirp from what sounds like the alternator belt (I assume it's a belt). They said they retensioned the belt and that should fix everything. The battery is a new gel battery, 3 months ago.

Here's the question. Is it normal for the low bat light to come on for 5 seconds when you start? It goes out if I rev up the engine. And is that chirp normal? It's less now but still there.

It's just that I paid a hell of a lot for BMW service and don't feel I got much. The dealer is also quite a distance away so taking the bike in is a pain in the butt.

[beemerphile]

I took the bike in for it's 10,000 km (6000 mile) tune up and had them check out why the low bat charge light would come on for about 5 seconds after starting. Also get an annoying chirp from what sounds like the alternator belt (I assume it's a belt). They said they retensioned the belt and that should fix everything. The battery is a new gel battery, 3 months ago.

Here's the question. Is it normal for the low bat light to come on for 5 seconds when you start? It goes out if I rev up the engine. And is that chirp normal? It's less now but still there.

It's just that I paid a hell of a lot for BMW service and don't feel I got much. The dealer is also quite a distance away so taking the bike in is a pain in the butt.

It is normal for the battery light to illuminate until you blip the throttle. No harm, no foul. Mine does the little chirping thing for a little while when cold. It goes away shortly. I have been riding BMW bikes for 30 years, and they have always made a cacophony of noises. Seems unusual for such an expensive machine, but they just do that. The key to peace of mind with a BMW is a good set of ear plugs.

[acejones]

My '03 does that. Its no big deal. I certainly wouldn't mess with a dealer on this.

[mbauman]

My '03 does it too. It's good not to be alone.

[JCsman]

Well, apparently they didn't "fix" it for 2004 as mine is in the same club. Let not your heart be troubled.

[challey]

Sebretian -
Here's the answer I always get about similar questions:

They all do that . . .

[Boxer]

Robbie (cyclerob) explained this once and although I remember the logic behind it I can't remember the details. Something to the effect of a protective feature of the alternator to not go into full charge mode until after the first blip of the throttle.
It made sense to me, and since mine has always done it...and still does at 52K miles...I have no reason not to believe it.

[Lobo1625]

I'm not sure if this is correct or not, but the alternator may be a self exciting type, similar to a GM 'one wire' style. It requires that the alternator be spun up to a certain RPM to begin producing electricity for the vehicle. After it has begun to produce electricity, dropping down below the rpm where it began to excite, it will continue to power the vehicle. Nothing to worry about, just blip the throttle after you start the bike so that the light goes out and smile.

[Sebretian]

Thanks. You'd think for what I pay in service rates they would just tell me that. Thank goodness for this forum and thank you all for the info.

David

[CycleRob]

The detailed explanation I posted may have dropped into the ByteBin of the old system on EZBoard. Lobo1625 is correct in his generalization. The alternator is a self exciting type.

For an excellent description how alternators work, with many diagrams, go to this WEBSITE and read the lengthy article

Adding to that, a conventional 3-wire alternator draws full field current when the engine is stopped and the key is on. Not a good thing for a battery or the alternator rotor's possible destructive heat buildup if you stall your vehicle and do not turn the key off. Newer systems like our 1150R has have improved and simplified the regulator's actuation power. That's where the rotor's residual magnetism comes in to power the regulator in the self excited type, but only after the engine starts and goes goes slightly above idle speed. On engine start the residual magnetism is not generating much power until the RPM's raise enough to power the regulator so it can apply field current to the rotor. Normally, automatic fast idles on engine start mask the delay before the charge lite goes out (at about 1,500 RPM), so it's not an event unless there is a fast idle start lever and the operator doesn't use it or the throttle on a hot engine start. The bike will idle and the charge lite stays bright, implying there's a problem, when there isn't any.
The best parts about this type of system are that potentially battery draining field current is cut off immediately if you stall the bike. You are also able to push start the bike with an almost dead battery, although a few thousand RPM's may be needed for several seconds to initiate self sustaining output.