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
IIRC you can get led's for automotive use with resistors built into the lamp.
John
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
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
Do you have to have a light for the alt?
I'dhave to have to diagnose the problem if the bulb failed, though!
David
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.
[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
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
------------------------
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.
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 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
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/
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.
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
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
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
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.
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. 
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.
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
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!!!!!
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
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
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
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
Splitrivet: What do you mean with ac application as alternator lamp?
I cant see any ac applications at all in a car, except for inside the alternator, before the main diods.
/Hasse
quote:
Originally posted by Hasse
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
OK hasse bad choice of words, should have said current can flow either way.
But as LED's are used the same way in AC circuit thought this was the best way of explanation.
Cheers
Bob
[Edited on 18/3/05 by splitrivet]
[Edited on 18/3/05 by splitrivet]
As I understand it the alternator lamp either has current flowing from battery to alternator (when alternator is not working), or when the alternator
is working the volatge is equal either side of the bulb, therefore ther is no potential difference across the buld and no current flows. hence the
buld goes out.
As I understand it current will only flow one way through the buld, its the nature of the circuit its in.
[Edited on 18/3/05 by clbarclay]
The current thru the lamp can flow the other way ie when the battery voltage is lower than the alternator a duff battery lets say will show itself by
as you increase revs your warning lamp gets brighter (more current flowing backwards to the battery) if the reverse happens its your alternator.
Cheers,
Bob
The main output from the alteranator goes to the battery + terminal?
If so then should not the alternator is increase the voltage on the battery side of the buld as well, 'equal' to the output of the wire
straight to the buld?
I've driven some vehicles with pritty duff batteries and haven't noticed the bulb iluminate whalst the alterantor is working.
To be honest I dont know if this is the case with a self exciting alternator,in which case only the battery lead is required to supply the field
voltage which is probably why NS Devs motor worked without a warning lamp either that or the diodes in the alternator were very leaky.
Cheers,
Bob
Is the attached wireing diagram for an alternator, it however is my understanding.
Is the diagram correct, over simplified or plain wrong for a typical alternator charging setup.
Rescued attachment alternator wireing.JPG
Found this site tells you all you need to know.
http://www.alternatorparts.com/understanding_alternators.htm
Actually is a pretty shite hot site with loads of info,got nowt to do with LED's though
Cheers,
Bob
[Edited on 18/3/05 by splitrivet]
oh dear! as i understand it 12v from battery flows through red warning/charge bulb to "ind" wire of alternator to earth when alternator stationary, when spinning the alternator is initially excited by thie ind supply and begins to generate, at which point the battery is then charged. if battery voltage initially was 12.2 alt output zero untill operating, once alt is spinning/operating its output being 13.4v this measurement will be the same as ind equal so battery/charge light goes out. some not all alternators will self excite to charge under heavy throttle but this is notr recomended as the norm. to be honest!!!!! whats really wrong with normal bulbs?