Unusual charging light behaviour (1976 Morini 3½ Sport)

[jpcoetzee]

Here's a brain teaser for the electrical wizards. The charging light on my 1976 Morini 3½ Sport is coming on... sometimes.

The regulator has been replaced with a Ducati reg which has a white wire coming from it, connected to a red light i.e. the light is suppose to come on if the battery isn't charging. But that light is coming on after I have riding for a few minutes. It only happens when all lights are off i.e. the ignition key is in the first position. The ignition key has two positions (and off). In position 1 the ignition is on but the all the lights are off, in position 2 the sidelights/headlights are on. When the switch is in position 1 there is no drain at all on the battery, because the central red wire to the alternator is disconnected and the bike doesn't have a electric fuel tap.

I wired a voltmeter across the battery and across the two yellow wires from the alternator. These are the voltages I saw while riding:

Code: Select all

Ignition             Charging   Voltage    Voltage
switch               Light      across     across 
position                        battery    yellow 
                                (DC)       wires (AC)
                                
1 (all lights off)   ON         15.3V      11.5-11.9V
2 (sidelights on)    off        15.2V      12.5-12.9V
2 (full beam on)     off        13.7V      15.5-17.0V

If I run with full beam for a few minutes then turn the ignition back to position 1, the voltage across the yellow wires drops over 20 seconds or so, back to 11.5-11.9V then the charging light comes on again.

Some more information:

* The battery is fully charged (using a battery charger)

* I'm blowing the headlamp and sidelight bulbs in the headlamp occasionally (this might be a red herring since other bulbs do not blow)

* There are no problems starting or running the bike. The lights work well and the battery charges i.e. the lights are bright without the engine running.

Some questions:

1. I suspect that the reason the light is coming on is that the battery is fully charged and there is no drain on the battery, so there is no charging current. Is this likely? Is this how it works?

2. Are the voltages as expected?

3. Why does the voltage across the yellow wires RISE when I turn the headlamp on?

4. Should I be worried?

Many thanks!

[elektrobank]

Some questions:

1. I suspect that the reason the light is coming on is that the battery is fully charged and there is no drain on the battery, so there is no charging current. Is this likely? Is this how it works?

2. Are the voltages as expected?

3. Why does the voltage across the yellow wires RISE when I turn the headlamp on?

4. Should I be worried?

Many thanks!

try to change your regulator.... usually the voltage on full charghe with engine running is 14.4, no more... you can suspect an imminent regulator failure... this can explain also the light-blow...

[jpcoetzee]

Which regulators with a warning light wire would work?