To led or not that is the question

[ChrisGadd]

So while the dash panel is off I thought I'd have a play with the dash lights.
Firstly I've tried two different types of led lighting for the speedo and rev counter both of which look good although the dimmer switch can't be used because the led's are not dimmable.
Also I've replaced the warning lights with ones that have removable bulbs and have changed the bulbs again with led's with varying results.
The indicator works only in one direction probably because the led's are pole specific. So kept the bulb in.
Also the headlight indicator didn't work at all on a led and the bulb only just glowed. There is what looks like a resistor in line which I can only assume is to reduce the flow from the warning light whilst driving in the dark. I have the option of removing the resistor and use a led or put in the bulb , not sure which any advice would be welcome

Edited by ChrisGadd on Tuesday 2nd June 19:37

Edited by ChrisGadd on Wednesday 3rd June 12:19

[tivi92]

clicky

You can change the language by clicking on the country flag

[Penelope Stopit]

Alternator needs 3 watt bulb or higher, it won't cut-in at low revs with an LED, it might not cut-in even at high revs

You could possibly use an LED for the alternator warning light by wiring it through a relay, a resistor of correct wattage would need to be wired in parallel with the relay coil

The LED still wouldn't function correctly after a modification

Edited by Penelope Stopit on Wednesday 3rd June 10:26

[tivi92]

This is not the case with my S3C, the behavior of the alternator has not changed here.
The LED goes out at the start and from 3,000 rpm

[GreenV8S]

tivi92 said:

This is not the case with my S3C, the behavior of the alternator has not changed here.
The LED goes out at the start and from 3,000 rpm

Not sure what you mean by 'goes out at the start', but with the original warning lamp these engines needed the revs picked up above idle to get enough current to energize the alternator. If yours needs 3000 rpm that's substantially worse and is worth fixing. The fix is to fit a parallel resister to increase the current so the alt will energize at a lower speed.

[Penelope Stopit]

tivi92 said:

This is not the case with my S3C, the behavior of the alternator has not changed here.
The LED goes out at the start and from 3,000 rpm

What? Your warning light goes out twice, once when started and again at 3000 RPM, it would have to extinguish, illuminate and extinguish again

An LED will not replace the alternator warning light bulb without modifications and even after modifications it will not function correctly

An LED is a diode, a diode can't possibly achieve what a bulb achieves when used as an alternator warning light

Perhaps you're unaware of what a bulb achieves

[tivi92]

@GreenV8S

My TVR S3C has been running perfectly with these LEDs since January 2017. After the 3,000 rpm has been reached and the LED of the alternator is off, the alternator also works below 3,000 rpm. Exactly as before the conversion to LED.
I do not understand what you mean.

[ChrisGadd]

tivi92 said:

clicky

You can change the language by clicking on the country flag

Many thanks I knew someone will have done this conversion although I cant find a dimmer switch that will work?

[tivi92]

@ChrisGadd
Is on the same page below.

[ChrisGadd]

tivi92 said:

@ChrisGadd
Is on the same page below.

The link doesn't find the dimmer switch

[Penelope Stopit]

It's not possible to replace an alternator bulb with an LED and have full functionality

The LED being a diode will only work one way

An alternator bulb has to and will illuminate when or if the voltage across it is of reverse polarity during alternator failure or circuit volt-drop

It's basics innit

[ChrisGadd]

Any idea where I can get the M5 dash fixing pins that are glued to the back of the dash?

Edited by ChrisGadd on Wednesday 3rd June 13:48

[QBee]

Try the BMW forum?

[O mage]

ChrisGadd said:

Any idea where I can get the M5 dash fixing pins that are glued to the back of the dash?

Edited by ChrisGadd on Wednesday 3rd June 13:48

Yes there called master plate studs here.

http://www.npfasteners.com/composites/master-plate...

[ChrisGadd]

O mage said:

Yes there called master plate studs here.

http://www.npfasteners.com/composites/master-plate...

Brilliant many thanks

[GreenV8S]

tivi92 said:

@GreenV8S

My TVR S3C has been running perfectly with these LEDs since January 2017. After the 3,000 rpm has been reached and the LED of the alternator is off, the alternator also works below 3,000 rpm. Exactly as before the conversion to LED.
I do not understand what you mean.

That is not 'running perfectly'. There was something wrong with it before you made the LED conversion - it should not be necessary to rev as far as 3000 rpm to energize the alternator. It's possible you have also lost the low voltage warning functionality that the original bulb provided.

[O mage]

GreenV8S said:

That is not 'running perfectly'. There was something wrong with it before you made the LED conversion - it should not be necessary to rev as far as 3000 rpm to energize the alternator. It's possible you have also lost the low voltage warning functionality that the original bulb provided.

I couldn't understand that at first but i think he's trying to say It is ok at idle and still works ok when the alternator spins up and the regulator kicks in.

[88S1]

tivi92 said:

clicky

You can change the language by clicking on the country flag

Cool site that, some good stuff to read and download.

[tivi92]

Penelope Stopit said:

It's not possible to replace an alternator bulb with an LED and have full functionality

The LED being a diode will only work one way

An alternator bulb has to and will illuminate when or if the voltage across it is of reverse polarity during alternator failure or circuit volt-drop

It's basics innit

The charge indicator light gets on a pole + from the battery. The other connection is at D +, i.e. at the + coal of the alternator. If the alternator is working properly, the charge control lamp + is on both connections. Since there is no voltage difference, no current can flow, the lamp remains dark. If the alternator is not working, the current flows through the + coal, through the armature winding, through the minus coal to ground and from there back to the battery. The circuit is closed, the battery voltage is present at the charge control lamp and it lights up.

It's basics innit

[Penelope Stopit]

tivi92 said:

Penelope Stopit said:

It's not possible to replace an alternator bulb with an LED and have full functionality

The LED being a diode will only work one way

An alternator bulb has to and will illuminate when or if the voltage across it is of reverse polarity during alternator failure or circuit volt-drop

It's basics innit

The charge indicator light gets on a pole + from the battery. The other connection is at D +, i.e. at the + coal of the alternator. If the alternator is working properly, the charge control lamp + is on both connections. Since there is no voltage difference, no current can flow, the lamp remains dark. If the alternator is not working, the current flows through the + coal, through the armature winding, through the minus coal to ground and from there back to the battery. The circuit is closed, the battery voltage is present at the charge control lamp and it lights up.

It's basics innit

Apart from the alternator cut-in RPM

The 3 watt or 5 watt alternator warning light bulb informs the driver of faults that you are unaware of

Battery positive volt-drop

Battery negative volt-drop

Worn brushes

Open circuit diode

Failing stator

and most important of all

Short circuit diode

With the ignition key removed, a short circuit diode will be applying a voltage to D+ (terminal 61) and an alternator warning light bulb will illuminate to inform the driver of the reverse voltage being applied to it which is earthing through the ignition circuit that is of positive polarity when on and negative polarity when off

When the above fault occurs there is a constant current draw through the alternator rotor winding and ignition relays will also hold-in

Basics innit, when understanding an alternator warning light circuit