One for the auto electricians.

[Martin Evans]

I recently had to replace the control box and dynamo on the Traveller. I was lucky enough to obtain two boxed genuine Lucas control boxes (One for a spare), of which http://morrisminorspares.co.uk/shop/pop ... hp?pID=778 is a copy.

I followed the procedure in the workshop manual, that said to disconnect all the wires from terminals A &A1 and join them together. Then with the voltmeter between D & E, I set the output screw (The output points especially were tarnished through years in a box but they took little cleaning and I reset the gap), ensuring to do it quickly, so as not to overheat the shunt windings. It wasn’t a very warm day and I set the output to just over 16V. With this done, I set the cut out to about 13V. All seems to be well.

All my previous cars have had alternators (Even my 1974 Mini had one), so the dynamo is a relatively new thing for me (I remember my father’s Lotus Elan had one). I have looked at the wiring and can see what goes where but I am curious to know what is the purpose of joining all the A and A1 wires together

Also the settings had a tolerance (The output was temperature dependant) and in the case of the cutout, it was something like 12.7 to 13.2 V, so I aimed for 13V. I know that without the cutout, the dynamo would turn into a motor at low RPM and with this in mind, wondered whether it is better to aim high rather than low

[suffolkpete]

The reason for joing the A and A1 wires is that the voltage regulator has two windings, a shunt winding and a tapped series winding. The shunt winding does the basic regulation, but the series winding carries the dynamo output current. Its purpose is to lower the dynamo output voltage when a high current is drawn as a form of overload protection. The two tappings on the series winding go to the A and A1 terminals which feed the various electrical loads. You remove them and connect them together during setting because if they were drawing current during the setup process, you would get a false setting, so voltage setting is always carried out with the A and A1 (why there are two I've no idea) open circuit. There is no need to worry about the cut-in voltage, the purpose is to make sure that the dynamo doesn't start to charge until the voltage is more than the battery, which will happen even at 12.7 volts. If you look at the drop-out voltage, you will see that it can be anything between 11 and 8 volts, so a certain amount of reverse current is permissible. The large difference between the cut-in and cut-out voltage is necessary to prevent the oscillation that would occur when the dynamo voltage drops suddenly as the load is connected on cut-in.

[Martin Evans]

Thanks for that; I'll copy it and keep it with the text books I have.

[m.thaddeus]

Thank you Mr. Suffolk -I am making notes.