Classic cars forum & vehicle restoration.

[Ray White]

How does it work?

I understand how power leaves the battery and passes through the ammeter and voltage regulator onto the ignition switch and from there to one side of the warning light. The other side of the light goes to the D terminal of the control box and earthed.

When the engine is not running (or only slowly) the dynamo will produce very little power so power from the battery will turn the light on.

When the engine runs faster power from the dynamo equalises that from the battery and cancels itself out ,,,so with no current flowing through it, the light goes out.

At this point I become confused. If current from the dynamo exceeds that from the battery going through the warning light, why does it not illuminate?

[ukdave2002]

In normal running the battery and dynamo voltage are more or less equal, so there is little or zero potential difference across the ignition lamp.

Dave

[Ray White]

[peter scott]

The ignition warning light receives power when the ignition switch is on and other side of the warning light is connected to the frame of the control box and the D terminal of the dynamo. With the dynamo stationary the frame connects to chassis ground through the shunt coil but when the dynamo gives sufficient output the frame rises to battery voltage so there is now no voltage across the warning light.

Peter
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http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

[Ray White]

Thank you Peter. I will go away and think about it.

[alastairq]

Or, does the bulb simply shine backwards??
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Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces.

[Ray White]