Classic cars forum & vehicle restoration.

Mello

I want to replace the weedy 6V lamps in my car with bright low-consumption LED replacement units, but can't find a UK supplier that specialises in old cars?

Any suggestions/recommendations? Thanks in anticipation...

Finch661 · Posted: Tue Sep 29, 2009 9:54 am Post subject:

have you tried farnell? (http://uk.farnell.com/) or rapidonline
it all depends on what you will be using the LEDs for?
_________________
1985 Mini Mayfare (1275)
1976 Mg Midget 1500

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

Try Paul Goff (Goffy). norbsa02.freeuk.com . He has an amazing variety of 6 and 12 volt L.E.Ds. all listed on the site. Also 6 volt BPF halogen headlamp bulbs.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

Phil - Nottingham · Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham

Ultraleds
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Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2

Peter_L · Posted: Tue Sep 29, 2009 8:11 pm Post subject:

LED's operate at about 2 to 3 Volts. Their spec sheet will show precise.

What is required is the maximum current flow of the LED and then using Ohm's law, taking your supply voltage as 6v, calculate the size resisitor required. 1/4 watt resistors will suffice.

LED's don't like heat on their legs, so take care when soldering and they are polarity conscious.

Google LED Voltage or look at Farnell spec sheets for a good guide.

You may find this interesting and helpful.

http://otherpower.com/otherpower_lighting_leds.html

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

LEDs are polarity conscious, but they will not be damaged by wrong polarity. They just don't light.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

Nic Jarman · Posted: Wed Sep 30, 2009 11:39 am Post subject:

LEDs are current driven devices.Use a resistor to get the right current, NOT VOLTAGE.
_________________
1936 Morris 8 Series 1
1973 MGB roadster
1977 MG Midget 1500
Dax Rush

Finch661 · Posted: Thu Oct 01, 2009 2:39 pm Post subject:

a lot of electronic comonent suppliers supply LEDs that are designed for automotive (6-12V) applications, and have built in current limiting resistors. i usually include a small/micro potentiometer in series with the LED to adjust the brightness!
_________________
1985 Mini Mayfare (1275)
1976 Mg Midget 1500

Nic Jarman · Posted: Fri Oct 02, 2009 11:19 am Post subject:

Using a pot as a current limiter is not a very good idea as they are supposed to be use as a variable potential divider and the reference voltage that they give is then fed to a transistor being used as a trans-conductant device. I hope that is clear enough. The best book to check these things out is " The Art Of Electronics" by Horowitz and Hall. It is a bit pricey.
_________________
1936 Morris 8 Series 1
1973 MGB roadster
1977 MG Midget 1500
Dax Rush

ukdave2002 · Joined: 23 Nov 2007 Posts: 4231 Location: South Cheshire

I agree with Nic

The resistor is there to limit the maximum current, protecting the LED. An led is a diode and for all intents and purposes a short circuit one way round and open circuit the other, diifernt LED will have different power ratings and require different size resistors.

There are many different types of LED around, the very low power ones fitted as a TV standby lamp will not be suitable even in a cluster for vehicle lamps.

Most of the direct replacement off the shelf vehicle LED lamps seem to be 12v, the simplest way to use these on a 6v system will be to add another resistor in parallel and of the same value as the fitted current limiting resistor (or replace with a resistor of half the original value). These 1/4 Watt carbon resistors will set you back about 5p! To identify what value of resistor is fitted Google “resistor colour code” and you will get a chart.

Dave

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

Surely you mean in series, not parallel, Dave.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

ukdave2002 · Joined: 23 Nov 2007 Posts: 4231 Location: South Cheshire

No in parrellel , ohms law I=V/R ; if you half the voltage you need to half the resistance to maintain the same current.

Jim.Walker · Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield

OK Dave, I see your point. I never was very good with solid state stuff! I still relate to running things like 2 x 6 volt bulbs in series (or a bulb and resistor) on 12 volts.
Thanks.
_________________
Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!

Nic Jarman · Posted: Fri Oct 02, 2009 4:27 pm Post subject:

The voltage drop for an LED is usually about 0.6v however the super bright LEDs have a forward voltage of 3 to 3.4v but still have a current of 20 - 30 mA. So conservatively 6v - 3v = 3v then R= V/I = 3/0.02 = 150 ohms and P = V2/R so that will give 0.06 watts. This should give a fairly low skin temperature. Now you can make your own.
_________________
1936 Morris 8 Series 1
1973 MGB roadster
1977 MG Midget 1500
Dax Rush

Peter_L · Posted: Fri Oct 02, 2009 4:39 pm Post subject:

Or perhaps this..

http://www.muzique.com/schem/led.htm

or this

http://led.linear1.org/category/led-basics/