928Myles

Hi, 1990 S4 auto with digital dash.
Some of my bulbs in the pod are out and I would really like to replace all of them with LED's. My car has a rheostat wheel for dimming the dash lights and have been told (by jaeger) that this would have little effect on dimming the LEDs.
I often carry out long night drives and like my dash lights as dim as possible to reduce eye fatigue.

Any electronics experts out there know how (if) I could modify the factory dimmer to better work with the LED's?

Thanks in anticipation,
Myles Garmonsway

Nicole

Hi Myles:

You can install a micro-potentiometer that will be able to adjus the brightness. I have never done this, though, and don't know, if any of my customers did.

Do you have a picture of your RUF steering wheel? I assume that's a non-airbag wheel, as i believe airbags for RHD cars weren't available until much later than 1990... still curious. Very!

Alan

Varying the voltage a little has a big effect on incandescent bulbs due to a non linear voltage to brightness curve. It has an effect but a smaller one on LED's becuase their brightness is effected primarily by current in a more linear way. The fact that LED's take much less current also means that having mostly or fully coverted to LED's the Rheostat will actually provide a such smaller maximum voltage drop (voltage change range) anyway.

So there are 2 effects here: rheostat is less effective at dropping voltage and the LED dims by less % even for the same drop.

If all your dimmed lights are now LED a larger resistance value Rheostat could work OK. If only some of your dimmed lights are LED's it will always be hard to dim the LED's this way without extinguishing the incandescents.

The best ways to dim LED's is with variable pulse width modulation at a fixed voltage - since even different characteristic (voltage drop) LED's will dim by the same proportion.

With a larger resistance rheostat you may still see some LED's dim differently as they get to lower brightness levels if their characteristics are very different. eg some LED bulbs have 2 extra diode voltage drops to make then non-polarized...

Alan

ibkevin

Here's some LED info...

https://rennlist.com/forums/showthre...ferrerid=15545

AO

Alan-

A quick google seach brought this article up.

http://www.autospeed.com/cms/A_2902/article.html

But this is for a single LED. Is there a way we could adapt his design for use with our cars? I assume we's need a larger resistor? Maybe a larger relay too? But I like the auto dim feature.

Rob M Budd

Use this LED dimmer.

I've had it in mine for about 3 years and installed a few for customers.

http://www.theledlight.com/pdf/controls/mini_dimmer.pdf

Rob M Budd

And you can put it on just the cluster LEDs so your regular dimmer still controls everything else.

928Myles

Thanks for the replies folks.

Nicole,
photo of the steering wheel. It also has a tall cassette box that I have not seen elsewhere, wooden shifter & small leather boot.

Myles

928ntslow

If you are just using a few LED's,(or the whole set up) it would pretty inexpensive to wire them into the circuit with a by-pass LV switch. Use a 1K resistor (maybe a 1.5K depending on how dim you want it). When the switch is in one position, you have full voltage, flip it to the other side and the current is routed through the resistor dimming the LED's to a a determined dimness dependent on the resistor rating. Probably about $5.00 worth of parts. No real need for the wheel as you probably already know what dimness you prefer.