locoboy
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| posted on 8/9/03 at 11:58 AM |
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Alternator wiring
2.0 pinto 3 wires out of alternator plug, 2 x fat red ones, 1 x skinny grey one.
Is skinny grey one used for the ignition light on the dash?
do both the other red ones go the the starter?
Cheers
Col
ATB
Locoboy
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David Jenkins
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| posted on 8/9/03 at 12:04 PM |
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Col,
Yes, and yes. 2 big fat red ones together make up the power output lead - they go to the same destination. 2 smaller leads are easier to handle than
the equivalent single large cable.
cheers,
David
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locoboy
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| posted on 8/9/03 at 12:14 PM |
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Ta v. much Dave.
Col
ATB
Locoboy
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stephen_gusterson
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| posted on 8/9/03 at 12:56 PM |
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beware, and dont get caught out like I did.
The alternator on my granada v6 donor - dunno what make - doesnt pruduce a charge unless it is connected to the dashboard indicator light. This has
been verified by others.
weird but true.
atb
steve
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Dusty
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| posted on 8/9/03 at 02:08 PM |
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The Ignition light circuit feeds a little electric current (3 Amps or so) through the slip rings into the rotating field windings to produce a
rotating magnetic field. This field 'cuts' the static windings inducing an AC current in them which is then rectified to DC and regulated
to 15 ish volts max to charge the battery. No field current, no magnetic field, no output. Once charging, voltage on both ends of the ignition light
circuit become the same so there is no flow of current and the light goes out.
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stephen_gusterson
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| posted on 8/9/03 at 02:32 PM |
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Hi Dusty.
Im an electronics person, and am familiar with how it works, but what I wondered was why it needs to use the bulb as a source of current.
The alternator is connected directly to the battery, so it can draw current there!
The bulb is usually rated at a couple of watts - the 3 amps you suggest wouldnt be possible through the bulb.
a mystery.....
atb
steve
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David Jenkins
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| posted on 8/9/03 at 02:36 PM |
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Probably just another automotive designer's way of doing 2 different things with one object - imagine the thought process...
"I need an indicator lamp to tell the driver when no current is being generated..."
"I need a bit of current to give the alternator a helping hand..."
"I wonder if..."
and so on.
David
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stephen_gusterson
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| posted on 8/9/03 at 03:08 PM |
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where the scheme gets really crappy tho is if you lose the bulb when it pops, your alternator packs up.
not clever
atb
steve
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VinceGledhill
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| posted on 8/9/03 at 04:17 PM |
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The alternator windings get their first amount of "excitement" via the bulb (oh errr missus) but then as soon as it starts to give some
output the alternator itself will put a feed on the bulb wire.
This will be enough to fully feed the 3 amps or so for the windings via the slip rings as indicated above.
Most alternators have a steel in the magnets (electro magnets inside the rotor) and therefore do hold some residual magnatism.
This is why most alternators do not normally need a bulb to start charging. I.E. if the bulb blows then you can usually still get a charge out of
them.
What happens is that the residual magnatism within the coils are enough to get it to start charging a little. Once it starts to charge a little then
the magnets increase, then it charges more, etc until it's working fully.
If you get one that doesn't charge with a blown bulb, then you are unlucky. Revving the nutts off the engine for a short while may get it to
work.
Bulb works because it gets a negative through the windings. Once the alternator starts to work the winding becomes positive. The voltage difference
across the bulb then becomes 0 (14 or so on one end and 14 or so on the other)
HTH.
Regards
Vince Gledhill
Time Served Auto Electrician
Lucas Leeds 1979-1983
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stephen_gusterson
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| posted on 8/9/03 at 09:55 PM |
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thats a great help and solves the mystery - thanks vince.
My alternator had been in storage for over a year - perhaps the magnetism decayed. As soon as I added the bulb it worked.
Another of life's mysteries. Whenever I have had a Lucas alternator fail, the light NEVER comes on! If your lucky it just very dimly glows at
you, but never brightly.
Is this just my experience everyone?
atb
steve
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Peteff
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| posted on 8/9/03 at 10:39 PM |
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I had a MK3 escort years ago and in the dark you could still see the charge light faintly, but the battery never failed so I ignored it. Just reminded
me of it when you mentioned them not showing a failure.
yours, Pete.
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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VinceGledhill
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| posted on 9/9/03 at 07:56 AM |
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There are 9 diodes in the rectifier part of the alternator. 6 for the actual charging circuit part and 3 for the light deminishing section. If one
of them goes open circuit you will end up with a voltage difference of 3 volts when charging.
This will manifest itself in a dim bulb which can be seen in the dark (3v through a 12v bulb) but because there is no problems with the other 6 output
diodes then you will experience no problem with the car and it's charging circuit.
This can be fixed by changing the rectifier. But another trip to the scrap yard is probably the cheaper option. Or probably the best bet would be to
live with it. Providing of course that it is charging the battery.
In general alternators have very few moving parts (slip ring and brushes) and on the whole are very reliable.
Regards
Vince Gledhill
Time Served Auto Electrician
Lucas Leeds 1979-1983
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Rob Lane
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| posted on 9/9/03 at 08:32 AM |
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Funny to watch the 7's list guys changing their warning bulbs for LED diodes then having a discussion as to why some systems stopped charging.
Till someone pointed out the need for a resistor as well due to very low current drawn by LED!
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locoboy
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| posted on 9/9/03 at 08:49 AM |
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hi there, electrical dummy here!
I cant get an ignition light working, the thin grey wire coming tom the alternator is it the +ve or the -ve?#
i have tried earthing the bulb and connecting the grey wire with ignition on (not engine running) and nothing happens.
any advice appreciated.
Col
ATB
Locoboy
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stephen_gusterson
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| posted on 9/9/03 at 10:48 AM |
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on my car, which I 'think' has a lucas alternator, the bulb goes to the lead, and the other side of the bulb to 'ignition on
12v'.
atb
steve
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VinceGledhill
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| posted on 9/9/03 at 02:23 PM |
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The wiring diagram for the ignition warning lamp goes like this. Please excuse my drawing.....
Ignition feed..... Warning Lamp...... via thin wire..... Alternator...... earthed through field windings of alternator.
To test bulb and wires..... put the ignition on and earth the wire at the alternator end (Thin wire NOT THE THICK ONES) and the light should come on.
If it doesn't then check the bulb and / or wiring.
Regards
Vince Gledhill
Time Served Auto Electrician
Lucas Leeds 1979-1983
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