The Triumph Dolomite Club - Discussion Forum

Hi all,
I’ve just fitted a set of green LED lights into my instruments. They’re a little too bright ! Has anybody fitted a dimmer switch ?
Thanks, Richard

It depends on what LED's you have fitted and whether or not they have a built in driver circuit. Many good quality ones have a built in constant current circuit. This keeps the brightness the same even if the voltage varies. So a "simple" dimmer will not work.

However, It may be possible to use a PWM (pulse width modulation) circuit to turn the LEDs on and off at a fast rate which will reduce the perceived brightness.Again it depends on what LEDs you have and any inbuilt circuit that is driving them.


If you can let us know what LEDs you have then I might be able to help further.

Roger

Hi Roger,

I asked the vendor and they replied...


Hi Richard,

We don't stock a solid state dimmer but if your rheostat is in good condition with a voltage range down to 9 volts you should find these dim. They start lighting at 9v and reach full brightness at 11v. They will react quicker than incandescent lamps though.

Kind regards
Classic Car LEDs Ltd

Does that shed some light on the matter ?

I got this set which gave me the right bulbs for a Dolomite...

https://www.ebay.co.uk/itm/184367572556

Thanks, Richard

I fitted some of those self adhesive green flexible LED strips round the instruments in my Elan and they were too bright. I put a resistance in the supply to cut the voltage to about 10 volts and they were fine then. In fact, thinking about it, I probably used an electronic voltage stabiliser, the sort that is used in classic cars for some of the gauges. They output 10 volts steady.

Just put a resister in-line on each lamp. Pennies!

Richard,

This was what I had in mind: -

https://www.ebay.co.uk/itm/Lucas-3R-Rhe ... Swy5Bau616

Expensive and you also need the knob but they are only a few pounds.

Glen.

GlenM wrote: ↑Tue Sep 08, 2020 12:38 am Richard,

This was what I had in mind: -

https://www.ebay.co.uk/itm/Lucas-3R-Rhe ... Swy5Bau616

Expensive and you also need the knob but they are only a few pounds.

Glen.

They wont dim LEDs

Dave

new to this wrote: ↑Tue Sep 08, 2020 7:09 am

GlenM wrote: ↑Tue Sep 08, 2020 12:38 am Richard,

This was what I had in mind: -

https://www.ebay.co.uk/itm/Lucas-3R-Rhe ... Swy5Bau616

Expensive and you also need the knob but they are only a few pounds.

Glen.

They wont dim LEDs

Dave

Not without a resistor in parallel with the LEDs, which might have to be small and high wattage, and so negate the low power advantages of the LEDs.

But if it's not powering too many LEDs, what would be the problem with a standard pot as a potential divider with a padding resistor between it's low end and earth, so the bottom of the pot is near the threshold voltage of the LEDs. Might need a bit of experimentation with different values, but the pots are like 99p each on ebay.

If there are too many LEDs to drive through a normal pot, then it probably does need a current amplifier between the pot and the LEDs. One of the PWM voltage converter / small DC motor controllers looks like a good choice.

Graham