Alternator Warning Light

[Jez Morton]

Steve,

just reread comments, you say you wired res in series with led ? this is wrong it should be wired parallel or across the led.

 

Jez

[sj-bradley]

The LEDs in the gauges already have the current limiting resistor inside which is why you can wire these directly to +12 volts and not blow them up.

 

Diodes allow current to flow one way only, so if you connect these IN REVERSE across the battery, they are ok. If you connect WITHOUT a limiting resistor, it's like dropping a spanner across the battery. Only the diode cannot take 100s of amps and WILL blow.

 

If you are getting 14 (ish) volts with the engine running, then the alternator is definitely working. I believe that the the warning light on the dash lights when there is a difference of 12 volts from the warning light wire to the main output wire on the alternator. This happens if the alternator is NOT turning.

 

Once the alternator is working, both the main wire and the warning light wire output the SAME voltage, so there is no difference and hence the dash light goes out.

 

Hope that helps?

 

Simon.

[sj-bradley]

So, just looked at your pictures.

 

pin 1 should be 0 volts when engine not running (so that the fuse feed goes through the dash light to ground and lights up)

 

Pin 1 should go to the same voltage as the main output when engine is running, so there is no difference in voltage at the dash light (both sides should be +12 ish volts - or what ever the alternator is putting out)

 

Voltage - or Potential DIFFERENCE is what makes electrons (the magic smoke) move inside the wires and makes things work ...

 

(Gee - I must cut down on these joss sticks ...

Simon.

[Thrashed]

Thanks for the suggestions. As a test can I use my bulb holder unit and disconnect my loom wiring and start from scratch? If I did. What would I wire to where as a test to check the alternator is working? I can then rule that out and start looking at the wiring loom.

[sj-bradley]

Pin 1 is your warning light (dash) connection so it should go from 0 volts (not running) to around 14 volts (running). You can check this with a volt meter.

 

If you then connect a lamp from battery (switched live i.e ignition if you can) positive -> lamp -> pin 1 alternator it should behave as you'd expect.

 

Simon.

Edited March 9, 2015 by Simon B

[Jez Morton]

Hold on a minute. The 1k resistor is used to provide the excitation voltage for the alternator not to current limit the led, that's why it's wired parallel it allows a small amount of current to flow from the alternator.

[Thrashed]

Hi guys, so I want to test 2 things. Is the alternator working correctly and is the wiring loom working correctly?

 

Treat me like the idiot I am! If is disconnect the current wiring from the alt and then start afresh. If I take a wire from pin 1 to a bulb holder and then to the battery and then a separate wire from pin 3 to the battery, I guess the bulb should work as normal? If it does work that will rule out the alternator. Is this right?

 

Thanks

[Longboarder]

Thanks for the suggestions. As a test can I use my bulb holder unit and disconnect my loom wiring and start from scratch?

Correct. Yes you can. Pull your present wires off terminals 1 and 3 and isolate them.

Take your bulb holder with a proper tungsten light in it. Stick a 6mm spade on one end of it and connect to terminal 3 on the alternator.

Take one fresh clean wire. Stick a 6mm spade connector on one end. Connect to the 1 terminal on the alternator.

Now take the free ends of both these wires and clamp them to the battery positive pole with a mole wrench (This gives both bulbs a constant live and bypasses all your wiring and the ignition switch)

The bulb will light. Switch on the ignition. The bulb should stay lit. Start the engine. The bulb should go out. Stop your engine. The bulb comes on again.

If this all happens alternator is good and it's your wiring that was wrong.

I suppose your alternator could be the other way round internally and you might need the bulb on 1 and the excitatory wire on 3. There is absolutely no risk in trying it with the bulb on 1 and the exciter on 3. The alternator is expecting a positive voltage input on both 1 & 3.

The light will extinguish with the engine running only when it's getting output voltage from the alternator coming back out from the L terminal. Nothing comes back out from the IG terminal so if the bulb was in that line it would stay lit.

 

Nigel

Edited March 10, 2015 by Longboarder

[Thrashed]

Thanks Longboarder, will give this a try tonight to rule out the alternator as the issue.

[alanrichey]

Hold on a minute. The 1k resistor is used to provide the excitation voltage for the alternator not to current limit the led, that's why it's wired parallel it allows a small amount of current to flow from the alternator.

This is interesting stuff, but can I just clarify this for my own education ? As I understood it the resistor is only there in case the warning bulb fails ? Normally the circuit through the bulb is enough to excite the alternator so the resistor only come into play if the bulb goes open-circuit ?

[nicko]

Alan, as I see it the resister is there to make an LED "look" like a bulb.

HTH

Nick

[theduck]

Yeh the resistor is there to increase the resistance from that of the LED to that similar to a "normal" lamp.

[Longboarder]

As I see it the LED is there to confuse the elderly. It's like re-inventing the wheel, giving it an almost friction free bearing but making it only able to rotate one way. It will do some of the things the old one did, better in some cases but it won't do all the things the old one did. It's actually a different thing and in many cases it's still best, cheapest and simplest to use the old style unit.

 

Nigel

Edited March 10, 2015 by Longboarder

[Thrashed]

I put the resistor in line to mimic having a proper bulb in the system as I have read that LED's don't draw enough current to switch out the light.

 

The diode turned up today so will try that as my first option.

 

Will keep you posted.

[alanrichey]

Alan, as I see it the resister is there to make an LED "look" like a bulb.

HTH

Nick

OK, so in that case you need a resistor in series with the LED to make it look like a bulb and then a resistor in parallel in case the LED fails