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alernator light
dave r - 21/3/07 at 10:11 AM

the alt needs a bulb to charge.. but whats the best way of doing it if you want to use a led and not a bulb ?

Guinness - 21/3/07 at 10:17 AM

Wire a bulb in, under the dash?

Mike

Mr Whippy - 21/3/07 at 10:19 AM

Hmm I'm not sure the LED will normally in this application as the wire that feds the light also supplies the start current (proper name I forget) to the alternator. Once the alt is upto speed and is producing a higher voltage than the battery the current is stopped and hence the light goes out. Question is - does an LED flow sufficient current to charge the alternator coils, probably not...

You could wire it in parallel but not directly through the LED.



[Edited on 21/3/07 by Mr Whippy]

BenB - 21/3/07 at 10:20 AM

It depends on the engine. Some setups are pretty tolerant of bulb resistances. The ST1100 meanwhile was a little git trying to get the right lamp resistance. Anything over a few ohms and the excitor circuit to the alternator stopped working preventing any output!!!
In the end I removed the lamp altogether!!!

[edit]

ie I had shorted it to ground rather than leaving the connection open.

[Edited on 21/3/07 by BenB]

Hasse - 21/3/07 at 11:23 AM

Put a paralell resistor over the diod and diod resistor, to create som "starting current" for the alternator. I use about 100 ohm in paralell, works OK on my cross flow.

02GF74 - 21/3/07 at 11:48 AM

quote:
Originally posted by dave r
the alt needs a bulb to charge..


not necessarily - there may be enoiugh residual magentrism for self starting - but suppliing current sure will help.

as ^^^^ said, resistor in parallel.

bear in mind the the LED will not show an over charging condition whereas a bulb will (unless you fit another LED the other way round).

tks - 21/3/07 at 01:30 PM

quote:


bear in mind the the LED will not show an over charging condition whereas a bulb will (unless you fit another LED the other way round).



Over charge???? if the bulb is 12volt bulb you will need 24VOLTS to lit it up correctly!!

24 - 12 = 12 volts!!

When applying 24volts to the car system you are already smoking and allot of stuff burns out..

Tks

02GF74 - 21/3/07 at 01:57 PM

quote:
Originally posted by tks
quote:


bear in mind the the LED will not show an over charging condition whereas a bulb will (unless you fit another LED the other way round).



Over charge???? if the bulb is 12volt bulb you will need 24VOLTS to lit it up correctly!!

24 - 12 = 12 volts!!

When applying 24volts to the car system you are already smoking and allot of stuff burns out..

Tks


Not quite true. Filament bulbs do not work in a binary fashion but will produce light in proportion to the power (i.e. voltage) put across them.

You'll probably find that 1/2 the rated voltage or even less is enough to light them, albeit dimly so you do not need to apply 12 V; I reckon if you alternator was at 18 V then the lamp would light up dimly.

And yes, as you say, other parts of the electrical system will start smoking but unless you have lights turned on, it will only be the ignition that will suffer..... but ofcourse you would have turned off the engine since you saw the lamp come on

dave r - 21/3/07 at 03:43 PM

ta for the infowill try 100ohm and see how it goes

tks - 21/3/07 at 09:45 PM

quote:

And yes, as you say, other parts of the electrical system will start smoking but unless you have lights turned on, it will only be the ignition that will suffer..... but ofcourse you would have turned off the engine since you saw the lamp come on


Nahh when you see the light comeing everything is already gone!!

Remember that the bulb only sees 6 volts when the system sees 18!

and how do you know that its overvoltage instead of just a dynamo wich is broken??

I'm 100% sure that the dynamo cuts itself down (into "selfdestruction" when it gets to > 16volts madd)


Tks

02GF74 - 22/3/07 at 04:15 PM

quote:
Originally posted by tks


Remember that the bulb only sees 6 volts when the system sees 18!

and how do you know that its overvoltage instead of just a dynamo wich is broken??



if alternaotri is not charing the lamp will be on all the time,

if it is over charging, it may be on when engine not running, then be off as revs increase and be on again when revs are higher still. Don't know for sure.

... but you will smell bad eggs as you lead-acid battery get's boiled.

02GF74 - 28/3/07 at 11:23 AM

CORRECTION. Having thought about it, the lamp or any LED will never light up for overcharging since there will be no voltage difference between alternator and battery.

Sorry for the misinformation but noone else spotted it