Proper dynamo output

Larry, back in the day when I did my apprenticeship, we used to set 12 volt regulators to 13.75 volts for lead acid batteries. Luckily, I’ve never had the misery of working on a 6 volt system, but logic would dictate you’re looking at 13.75/2 = 6.9 volts.

I’m guessing you know that dynos don’t charge at very low rpm, as there is little to excite the field. So you need to raise the rpm to a reasonable level when setting it up.

Good luck, Norman

There is a lot of info in the technical library. Two main ones to look at:

In Lucas Catalogues – “Lucas Generator and Control Box Tests” Page 6 and “Generator Output Control” Page 22. There is also a lot of good information in the Lucas Overseas Training Manuals which are in the Library.

The French units are probably similar but I am not familiar with them. However the voltage values are going to be basically the same.

Assuming that the French units have current compensation, the open circuit voltage (with a piece of card in the cut-out contacts (as per P6 in the tests) should give a dynamo output of 16 – 16.5 Volts  for 12 Volt systems and 8 – 8.5 Volts for 6 Volt systems. (3000 rpm DYNAMO SPEED 20 deg C).

I am not sure what the ratio is between engine speed and dynamo speed, bearing in mind that it is driven from the camshaft at half engine speed but with a step up between the driving and driven pulleys.

When the battery is in circuit or lights are on, the current from the dynamo flowing through the current winding reduces the voltage to prevent excessive dynamo current but allows full charging of the battery as the charging current reduces.

I must go and check mine because I checked it the other day after I left the lights on and flattened the battery rather more quickly than I expected. When I checked it, I had a figure of 14.5 Volts in mind. That would probably be correct for a Constant Voltage Control but not for a Compensated Voltage Control.

I hope that I have not muddied the water too much.

Roger G