supercat
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 posted on 15/7/04 at 04:26 PM |
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LED's for dash warning lights
Hi Guys,
I want to replace the bulbs in my dash warning lights with LED's to provide a bit more brightness - i've seen superbright LED's in
maplin in the colours I need. My question is to I need to do any fancy electrickery to make them work or can I just bung them in with a resistor on
one of the tails?
Thanks,
James
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spunky
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| posted on 15/7/04 at 04:36 PM |
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IIRC you can get led's for automotive use with resistors built into the lamp.
John
The reckless man may not live as long......
But the cautious man does not live at all.....
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Markp
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| posted on 15/7/04 at 05:09 PM |
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I was looking at doing this,
One question popped up in my head
And LED in my understanding will only allow the electric current to flow one way through it??
When it comes to the red light from the alternator, it has a current going to the bulb and when the alternator is running it produces another current
that also goes to the bulb (this puts the red light out)
Make sense??
Will the fact the bulb is now an LED make any difference?
stupid question I know so please slap me down for it!!!!
Mark
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paulf
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| posted on 15/7/04 at 09:07 PM |
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You must use a conventional bulb for the alternator warning light as it has to flow enough current to allow the alternator to energise.Leds use very
little current which is a good reason for using them in some applications.
I think that the super bright ones may be to bright for night time use .
Paul.
quote:
Originally posted by Markp
I was looking at doing this,
One question popped up in my head
And LED in my understanding will only allow the electric current to flow one way through it??
When it comes to the red light from the alternator, it has a current going to the bulb and when the alternator is running it produces another current
that also goes to the bulb (this puts the red light out)
Make sense??
Will the fact the bulb is now an LED make any difference?
stupid question I know so please slap me down for it!!!!
Mark
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Viper
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| posted on 15/7/04 at 09:37 PM |
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Do you have to have a light for the alt?
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David Jenkins
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| posted on 16/7/04 at 08:07 AM |
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I'dhave to have to diagnose the problem if the bulb failed, though!
David
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supercat
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| posted on 16/7/04 at 09:15 AM |
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quote:
Originally posted by paulf
You must use a conventional bulb for the alternator warning light as it has to flow enough current to allow the alternator to energise.Leds use very
little current which is a good reason for using them in some applications.
I think that the super bright ones may be to bright for night time use .
Paul.
Ah i didnt know about the altenator light but that makes sense. I will probably only use LED's for the shift light, and oil and brake warning
lights. I don't do much night driving anyway in the tiger so over brightness shouldnt really be a problem.
Cheers,
James
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paulf
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| posted on 16/7/04 at 08:52 PM |
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[I mentioned it because I have used them for the indicator warning lights and am considering using an extra resistor and relay to dim them when the
lights are on.
Paul.
quote]Originally posted by supercat
quote:
Originally posted by paulf
. I don't do much night driving anyway in the tiger so over brightness shouldnt really be a problem.
Cheers,
James
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mad4x4
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| posted on 19/7/04 at 05:09 PM |
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James for a standard LED all you need is a Resistor. This is of a diesgnated value to limit the current through the LED.
Standard Led have a typical current draw of 20mA (28mA for Really Bright).
So using Ohms Law
v = I / R
12 Volt Systems
------------------------
that imples that R= V / I
which equals = 12 / 0.020
R= 600 Ohms
Or for Brighter
=12 / 0.028
R= 428 Ohms
5 Volt Systems
------------------------
that imples that R= V / I
which equals = 5 / 0.020
R= 250 Ohms
Or for Brighter
=5 / 0.028
R= 178 Ohms
24 Volt Systems
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that imples that R= V / I
which equals = 24 / 0.020
R= 1200 Ohms
Or for Brighter
=24 / 0.028
R= 857 Ohms
Hope this helps....... Remember a Diode will only light in one direction.
Scot's do it better in Kilts.
MK INDY's Don't Self Centre Regardless of MK Setting !
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hortimech
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| posted on 19/7/04 at 07:12 PM |
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now I know nothing about car alternators, but I bet that they are the same as groundscare machinery ones ( big lawnmowers ). they have builtin
electronic regulators and have three wires going to them.
a big output wire
a wire from the warning light
and finally a switched 12v positive power source to energise the alternator.
now here is the clever bit, the warning light wire is actually the earth or 0volt wire and when the alternator starts to charge it shuts off the earth
and the light goes out. this is why, when an alternator starts to have problems the light can sometimes come on faintly, it is getting an earth but
through heavy resistance
So in my opinion, for what it's worth, you should be able to use a led instead of a bulb
Why does everything happen to me
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supercat
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| posted on 20/7/04 at 09:41 AM |
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I think its time to pop down to maplins and get a few LED's and resistors and have a play! Thanks for the replies guys.
James
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BMF
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| posted on 20/7/04 at 01:33 PM |
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I bought one of the LED warning light modules for £30 from the Newark show, looks really good and is SVA compliant!
http://www.lightninglooms.co.uk/
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sting
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| posted on 20/7/04 at 01:35 PM |
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i`ve just ordered a `Bright 6` Warning light module they were at the Newark Kit Show cost £29.99 but it looked neat and SVA compliant. Won`t recieve
it til tomorrow so will post what its like then.
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mad4x4
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| posted on 22/7/04 at 12:47 PM |
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QUOTE think its time to pop down to maplins and get a few LED's and resistors and have a play! Thanks for the replies guys.
Maplin do some nice chrome mounts for the 5mm LED's
To help with SVA compliance you can "sand"down the top of the LED so it flush with the mount. LOOK at the Clear range they do yellow
red blue and green,
Look great
Scot's do it better in Kilts.
MK INDY's Don't Self Centre Regardless of MK Setting !
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NS Dev
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| posted on 16/3/05 at 11:34 AM |
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quote:
Originally posted by hortimech
now I know nothing about car alternators, but I bet that they are the same as groundscare machinery ones ( big lawnmowers ). they have builtin
electronic regulators and have three wires going to them.
a big output wire
a wire from the warning light
and finally a switched 12v positive power source to energise the alternator.
now here is the clever bit, the warning light wire is actually the earth or 0volt wire and when the alternator starts to charge it shuts off the earth
and the light goes out. this is why, when an alternator starts to have problems the light can sometimes come on faintly, it is getting an earth but
through heavy resistance
So in my opinion, for what it's worth, you should be able to use a led instead of a bulb
I have wondered about this exact problem in the past, and it would seem that on old vehicles with separate regulators, the warning light wire gives
the excitation for the alternator, but on later ones with built-in regulators, you are quite correct.
I actually went to the lengths of using a bulb for the alternator warning and LED's for the others on my grasser, then found out about the
change. I will use LED's on the 7 and will change to an LED on the grasser as the vibration continually blows the bulb.........the alternator
still charges fine without it but I don't know whether it is or not!!!
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MikeRJ
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| posted on 16/3/05 at 01:35 PM |
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quote:
Originally posted by mad4x4
James for a standard LED all you need is a Resistor. This is of a diesgnated value to limit the current through the LED.
Standard Led have a typical current draw of 20mA (28mA for Really Bright).
So using Ohms Law
v = I / R
12 Volt Systems
------------------------
that imples that R= V / I
which equals = 12 / 0.020
R= 600 Ohms
Or for Brighter
=12 / 0.028
R= 428 Ohms
You should also take into account the forward voltage (Vf) of the LED itself, which varies from about 2volts for red up to 3.5 to 4 volts for blue and
white. Obviously it dosen't make so much difference on 12volt systems, but on a 5 volt system you would end up with a very dim LED.
e.g. a blue LED with Vf = 4.0 volts and If=20mA on a 12volt supply
R = V/I
R = (12-4.0)/0.020 = 400 Ohms.
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clbarclay
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| posted on 16/3/05 at 01:47 PM |
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RS have proven very good for LED's etc. for me in the past, and thier website gives info on a wide range of LED's you will need.
Some of there LED's also come with built in resistors, suitable for 12v circuits.
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Peteff
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| posted on 16/3/05 at 01:55 PM |
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I've just helped with a Bright 6 module on a friends car. Follow the diagram and they are a nice piece of kit, wired the oil warning light up
today to finish most of it off. He's used a Premier loom with Sierra switchgear and the module mentioned plus a set of VDO gauges. The
aftermarket suppliers ought to get their heads together and agree on a colour code though as I have the attention span of a gnat these days and have
to keep looking to remind myself what goes to what. 
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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clbarclay
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| posted on 16/3/05 at 02:04 PM |
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Just what do you get for your £29.99 other than an LED and some plastic?
As for colour coding, when I wired in a new headunit to my old car, the new head unit had one colour code, the universal din plug had another colour
code, the car had a colour code all of its own and to top it of the new rear speakers had wire colours normally associated with front speakers.
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Hasse
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| posted on 17/3/05 at 11:32 AM |
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LED for all functions works for me.
If you want a LED also for the Charge function, I propose you connect a paralell resistor of around 60ohm over the LED and its serial resistor. This
provides the nessesary current to set the alternator to charge.
If you have an alternator with the normal 3 connections for B+, D+ and ground, internal regulator or not doesent matter, it would normally need the
current from the charge lamp to start charging.
Only very new alternators, normally with more than 3 connections, only require a voltage (very low current) on the 15 conection to switch into
charging. These alternator often have possibilities, and an extra lead for this, to sense the actual battery voltage and regulate the charging voltage
to this.
/Hasse
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NS Dev
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| posted on 17/3/05 at 12:09 PM |
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This confuses me, as on my old Opel manta, which I had fitted with the Vauxhall XE 16v engine (with std alternator) The warning light wire kpt coming
off. I drove the car for 5 months with it not attached and it seemed to charge just fine!!!!!
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Bob C
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| posted on 17/3/05 at 12:24 PM |
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with enough revs the remanance of the iron core should give enough volts for the internal diodes to power up the field circuit.
So it probably won't charge if you just tickover, but could "burst into life" when the revs get high enough.
I wouldn't expect this to always happen, but could explain NS Dev's observation
Bob
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Hasse
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| posted on 17/3/05 at 01:32 PM |
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Sufficient current from the charging lamp is "the sure way" to start the charging. Without this current, it may start from remaining
remanens in the iron, but is not given at all, that the the charging will start.
Maybe it will also depend on how long the alternator has been "resting" since last used? Every day use could then maybe be positive to
achieve charging.
/Hasse
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David Jenkins
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| posted on 17/3/05 at 01:48 PM |
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If you look at the wiring diagram for the Bright6 module HERE (click on the Bright6 link to
download) you will see that they wire a diode and resistor in parallel to the LED, with the diode pointing in the opposite direction. In this way I
guess that it behaves much like an ordinary light bulb as far as the alternator is concerned.
David
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splitrivet
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| posted on 17/3/05 at 05:18 PM |
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Sorry to disagree mad 4x4 but you dont use ohms law to work out resistors for LED's.
When you buy the LED make a note of the forward current (If), and forward voltage (Vf).Vs is supply voltage.
Then use this formula, resistor= (Vs -Vf)/If so r =(12-2.5)divided by 0.02 therefor an LED with a 12 volt supply,a 2.5 forward voltage and a forward
current of 0.02 would need a resistor of 475 ohms.
If you were using a LED for an AC application such as Alternator lamp use a silicon diode in reverse parallel and halve the value of the resistance
that you worked out from above.
Hope this makes sense.
Cheers,
Bob
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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