Why do my lights get brighter when I rev the engine?

[Sid Squid]

Originally Posted by yorkie_chris

Re. the "when you rev the engine" comments... last time I checked, I seem to remember my alternator putting out around 40VAC (open circuit) at tickover. So, the regulator is always in action and needing to do it's stuff.

That's when there's no load, when connected the voltage will drop significantly.

[BillyC]

Originally Posted by Baph

By upgrading bulbs (eg, Osram Nightbreakers as stated), the bulbs are designed to glow brighter. This is accomplished by drawing more current due to lowered resistance in the coil. If the alternator isn't putting out maximum current (for the bulbs) they will be dimmer than they can potentially be. When the current raises (by revving the engine), naturally the bulbs get brighter.

A 55W bulb, is a 55W bulb... no matter how bright or dim it is... put 12v through it and it'll draw about 4.6 Amps.

[Edit] Just to add... what makes a bulb 55W is a factor of its restistance, and the voltage that is applied to it, as demonstrated by the simple equation: I=V/R.

The headlight is rated 55W at 12V... which means its resistance is approximately 0.2 Ohms. Since the bulb's resistance is constant (for the sake of argument), only a reduction in voltage will cause the current to drop.

So for the bulb to get dimmer... it must have a varying voltage put through it. Enough... I'm bored now.

Originally Posted by BillyC

A 55W bulb, is a 55W bulb... no matter how bright or dim it is... put 12v through it and it'll draw about 4.6 Amps.

[Edit] Just to add... what makes a bulb 55W is a factor of its restistance, and the voltage that is applied to it, as demonstrated by the simple equation: I=V/R.

The headlight is rated 55W at 12V... which means its resistance is approximately 0.2 Ohms. Since the bulb's resistance is constant (for the sake of argument), only a reduction in voltage will cause the current to drop.

So for the bulb to get dimmer... it must have a varying voltage put through it. Enough... I'm bored now.

Simplest things to remember is fundamental electrical formulas.

V=IR I=V/R R=V/I. (Ohm's triangle) and P=IV(and the cos of the angle but it's generally ignored) or P=V^2R. As long as you know those you should be fine.

[Binky]

This may have been mentioned earlier. Sorry if so...

My headlights also differ in strength depending on the revs. When i'm stopped at lights for example the dash lights are almost flickering as if on thier last legs but when i get going and rev the engine they stay quite bright and at a solid strength. Is this just a part of the SV's electric or something to think about???

Originally Posted by Binky

This may have been mentioned earlier. Sorry if so...

My headlights also differ in strength depending on the revs. When i'm stopped at lights for example the dash lights are almost flickering as if on thier last legs but when i get going and rev the engine they stay quite bright and at a solid strength. Is this just a part of the SV's electric or something to think about???

i'd say if your worried check the voltage on the output of the rectifier if it's 16v + be prepared to replace to save a battery + breakdown etc . .

[Sid Squid]

Originally Posted by Binky

My headlights also differ in strength depending on the revs. When i'm stopped at lights for example the dash lights are almost flickering as if on thier last legs but when i get going and rev the engine they stay quite bright and at a solid strength. Is this just a part of the SV's electric or something to think about???

Read my posts above, at tickover the system voltage can drop below the battery's voltage, thus the battery's level of charge/condition will be the important factor, but clearly a check of the charging system is in order. Do you have any actual electrical problems? Assuming not, my first thought would simply be that your battery is a bit tired, it's output voltage is simply a bit lower than needed to keep everything bright.

Originally Posted by thor

Perhaps the battery is on it's last legs? I have some heated grips on, but that's it.
Also, The top half of the brake lights are dimmer than the bottom half. They also get dimmer when the indicators are on.
Any help gratefully received as always...

Maybe I have missed something, but I can't see where Thor's original observation was explained???? Unless it was covered by Soulkiss's comment that "pre K5/6 have this fault".
As you can guess, I have this peculiarity on my K3

[Sid Squid]

Bloody hell - Leigh!

Where have you been all this time?

What?? Is it doing it a lot or something? They all do this, cars included.

Helllloooo SS, can't get about so much now due to increasing age
Regarding the rear light, I understand the flickering at low revs, its the bottom half being brighter than the top half, especially when the indicators are working.
If this is a well known fault I'll change it, but just needed to clarify the point.