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Help..ongoing alternator
pointy - 13/8/08 at 05:02 PM

all,

I have now done a drawing of how my alternator is wired up thru the starter key.

Alternator still not charging and I have now tried 2 different units.

Is my wiring correct.

Andy p

[Edited on 13/8/08 by pointy]

rallyingden - 13/8/08 at 05:20 PM

From the ignition switch the thin wire should go via a bulb to the small terminat on the alternator

From the large terminal on the alternator the thick wire should go to battery +ve

When you put the ignition ON the bulb should light. When the engine starts the bulb should go out. If this does not happen then its a faulty alternator.

RD



...........ign sw bulb
+Ve ----- / --------O------------Alt small terminal.

+VE =================Alt large terminal

[Edited on 13/8/08 by rallyingden]

pointy - 13/8/08 at 05:23 PM

Ok,

I dont need a light as it is a race car however I do have an oil warning light that goes out after the car starts.
So is the way I have wired it up correct.


Andy

rallyingden - 13/8/08 at 05:27 PM

Not 100% sure if you need the bulb but it will tell you if you have excitation current flowing ie Bulb on and also charging voltage when running ie bulb off.

Have you also checked that the earths are good from alt body to engine to -Ve

What kind of alternator is it ?

RD

pointy - 13/8/08 at 05:36 PM

Lucas alternator.

Only 2 wires from alternator as shown on my sketch.

Earth wire from battery to chassis of body ok as car starts etc, but just not getting the charge back into battery!!! bit frustrating now.

britishtrident - 13/8/08 at 05:55 PM

Lucas 3 termminal alternator
--- 2 heavy wires to battery +ve
-- 1 light duty wire to the ignition sw via bulb

[Edited on 14/8/08 by britishtrident]

daviep - 13/8/08 at 06:38 PM

Very simple to test alternator independently of the vehichle wiring, you need a volt meter, a 12v test lamp and a piece of wire(and some crimps) .

1: Remove all wiring from alternator
2: Check alternator is correctly earthed
3: Connect 12v test lamp between battery positive and the warning light terminal on the alternator

At this stage the test lamp should light if it does proceed to step 4. If it doesn't connect the test lamp between battery +ve and the alternator casing (it should light) to verify the alternator is correctly earthed. If it is correctly earthed then there is a problem with the alternator.

4: Connect a wire (heavyish if possible) between battery +ve and the output (large) terminal of the alternator, nothing should happen

5: Start the engine, the test lamp should go out now to indicate the alternator is charging, if it stays lit again problem with alternator. If it goes out the alternator is working correctly which can be verified by checking battery voltage. In this case there is a problem with the vehicle wiring.

Sorry this is so long winded.

Davie

02GF74 - 14/8/08 at 08:22 AM

the small 4.7 mm connector on alterantor goes to a small bulb and then to switched 12 volt, done by ignition switch.

You cannot connect it to 12 V as this effectively shorts out the battery!!! The buld is there to limit current.

The way you have wired larger 7.9 mm connector to battery on the igniton switch is fine - I assume that the right hand post in you diagram is the live side and the left side becomes live when the switch is turned.

procomp - 14/8/08 at 08:51 AM

Hi

Just one thought. On the back of the MSA cut off switch. Have you got the 11 watt resistor wired from the spade terminal ?.

It is this resistor that stops the alternator blowing its diodes etc when the switch is turned of while the engine is running.

Also it is best to have a charge light on the car as this will tell you if the alt is working or not every time you start a race. And you now how it feels if you can't restart the car due to a dead battery during a red flag / spin. Plus dont forget if alt is not working you are excluded from results if it is checked by the screeners after the race.

Basic wiring diagram for the FIA version of the battery cut off switch.
Basic wiring diagram for the FIA version of the battery cut off switch. [/img]

Cheers Matt

Paul TigerB6 - 14/8/08 at 09:55 AM

quote:
Originally posted by rallyingden
From the ignition switch the thin wire should go via a bulb to the small terminat on the alternator


Agreed - must go through a bulb or the Lucas alternator wont start charging. I found this out when i changed all my filament bulbed warning lights for LEDs and the alternator stopped working - it wasnt getting the excitation charge with the LED

02GF74 - 15/8/08 at 08:23 AM

quote:
Originally posted by Paul TigerB6
Agreed - must go through a bulb or the Lucas alternator wont start charging. I found this out when i changed all my filament bulbed warning lights for LEDs and the alternator stopped working - it wasnt getting the excitation charge with the LED



Correct. Lamp would draw 10 x the current that a LED would - in theroy it still should be enough current to self-excite the alternator but a olution is to fit a resistor across the bulb - is what I have done and it works. The LED response time is far quicker than a filament bulb so you can see the LED flashing but once the alternator has "kicked in" it stops.

wilkingj - 19/8/08 at 01:53 PM

The 12volts via the Bulb to the small terminal provide the exciter current to fire up the current generation when the alternator first starts turning.

Once the alternator is generating, the alternator end of the wire climbs to +12v, thus extinguising the bulb.

You DO need the bulb as it acts as a ballancing resistor for the differing voltages at each end of the ciucuit. Even if you are racing. Its a bulb and a bit of wire. Hardly anything that will affect the performance from a weight point of view.