Turn signal/headlight dimming question

[jimmyenglish]

I was wondering the other day why my lights dim in unison with the turn signal or brake being on? I've noticed this on every motorcycle (except my K75, which has the same Odyssy battery my Venture has) I've ever owned. Battery is good but even when the battery was brand new it would do this. Voltmeter always reads good. I started thinking about this because I've never noticed this on a car, only on bikes. My wife has a crappy 98' Opel Corsa 1 liter that has a battery barely bigger than the one in the Venture and the headlight/dashlights don't dim when the signal is on. Just curious. Thanks!

[Flyinfool]

The alternator of a car is a LOT more powerful than the charging system of a motorcycle.

What is happening is that the extra 54 watts (27 W per bulb x 2 bulbs) of lighting that is flashing on and off is more amps than the stator can deliver at idle. Whenever you pull more amps than the charging system can deliver the voltage of the whole system drops. When the voltage drops the lights will dim. A car alternator is more able to deliver the needed power even at idle so the other lights do not dim.

[jimmyenglish]

Thanks Jeff. Just been a pet peeve of mine for a long time now.

[Guest tx2sturgis]

I will add to what Jeff said:

 

If you see this during idling, its more or less normal. But at normal road speeds, your headlight should stay at normal brightness during turn and brake light activation.

 

Also, automobiles use alternators, and most (not all) motorcycles use a stator.

 

They both have the same end result, but the operation is a bit different, since a stator will not put put out much current at idle. In fact, some bikes will DRAIN the battery if idling, and only charge the battery when the bike is being ridden at a few thousand RPM or more.

 

Long story short, unless the headlight dims noticeably while riding when using the brake or turn signals, you should be ok.

 

Of course, if you ARE having voltage or charging problems, you will find out soon enough when the bike wont start!