Bizarro
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| posted on 18/12/12 at 02:47 PM |
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Alternator and led ignition light problem
I have a problem with my ignition light/alternator where the light illuminates brightly with the ignition on engine not running, when I start the car
the ignition light dims to about half brightness?
The alternator is working properly ie Im getting 13 volts across the battery terminals with everything running, rev the car and the volts rise.
On the terminal at the back of the alternator, going to the ignition light, I only have 1v when stationary and this drops to milivolts with the engine
running, Im using savage LED ignition light so I guess the milivolts are enough to keep the led illuminated dimly?
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big-vee-twin
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| posted on 18/12/12 at 04:27 PM |
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One of the quirks using LED instead of a bulb.
Charging light works using potential difference, by having 12v on one side and earthing itself through the alternator, when the alternator spins a
voltage appears(12v) on the pin thereby the bulb goes out because it has 12v on each side therefore PD is zero, or glows dim if the alternator is not
charging properly.
An LED requires very little voltage to make it light, so can glow dim even when alternator is up to speed, may need to introduce a resistor in series
with LED.
Some alternators use the current flowing through the charge light to excite the alternator initially to get it working, so a incorrectly selected
resistor may stop it charging.
Simplest option is to use a bulb.
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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Bizarro
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| posted on 18/12/12 at 05:30 PM |
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Thanks, would it make any differance which side of the LED I try a resistor?
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big-vee-twin
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| posted on 18/12/12 at 07:03 PM |
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No its a series circuit, try a low resistance first and work up.
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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britishtrident
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| posted on 18/12/12 at 08:39 PM |
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(1) at 13v the alternator won't charge the battery you need a minimum of 13.4volts under load.
(2) Surely you need the resistor in parallel with the led to provide the exciting current for the alternator.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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philfingers
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| posted on 18/12/12 at 09:35 PM |
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I had this problem on a Westfield years ago, there was something like a 1.2w bulb in there instead of a 3w one. Basically as others have said it
excites the windings, without it it won't charge correctly, or with a lower powered bulb will charge poorly as in my case. It will charge when
you rev it hard, say 3-4k, but it should be charging at tickover.
if we assumed 3w bulbs (check to see what's normally used in the donor) then that would require a 0.25A. So Resistor would need to be 48R
[ohms] and 3w. I think that's right. The LED and it's series resistor would need to go in parallel to the 48R resistor. The series
resistor needs to drop 10v [as an LED needs 2v @ ~20mA], so around 500R [ohm]
If I get chance I could check this out at work tomorrow. Anyone shout up if i got my sums wrong!
[Edited on 18/12/12 by philfingers]
The true home of cars born under the Sylva name - http://jpsc.org.uk/forum
STM Phoenix R1
Sold-Sylva Striker 1300xf, 40s etc
Sold-Sylva Phoenix, 1300xf, BVH, 234cam, 2xDCOE 40s, live axle - 'old school', rally car and a few bikes
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big-vee-twin
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| posted on 18/12/12 at 09:52 PM |
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Agreed what you need to do is simulate the resistance of the original bulb, the parallel circuit formed by led and resistor will alter resistance of
the 48 ohm resistor.
Best find out details of original build and then reproduce same resistance
As said earlier easiest way is to use a bulb
Oh and don't forget the LED is a diode and will not work if its connected the wrong way round.
Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016
http://www.triangleltd.com
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philfingers
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| posted on 18/12/12 at 11:30 PM |
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yes, but it's negligible , the result is around 44R, which means slightly higher power.
I'm sure it will work.
My Westfield wouldn't charge in traffic basically, sit on the motorway for 100 miles was fine but an hour in traffic with lights on would see it
flat
The true home of cars born under the Sylva name - http://jpsc.org.uk/forum
STM Phoenix R1
Sold-Sylva Striker 1300xf, 40s etc
Sold-Sylva Phoenix, 1300xf, BVH, 234cam, 2xDCOE 40s, live axle - 'old school', rally car and a few bikes
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