Modernising A Classic Design

We visit Classic Dynamo and Regulator Conversions Ltd, a company that specialises in making sure classic vehicle charging systems are more than capable of coping with 21st century motoring, and receive a crash course in getting the most out of your classic’s electrics from CDRC boss Pete Jury.

A dynamo is essentially just copper wires spinning between two electromagnets. The more current you put into those magnets, the stronger the field becomes and the more electricity the dynamo generates. When the dynamo is not required, turning down the feed to the magnets turns down the output from the dynamo – this is what the regulator does.

The faster you spin a dynamo the more it outputs, so you have to control the output at higher engine revs. Before regulators came into use, they did this in the 1920s by developing the three-brush dynamo – the two main brushes cope with the charging currents, but the third brush picks up current from the commutator and feeds it to the field windings (magnets). Moving the position of this third brush around the commutator changed how much current it picked up and hence the dynamo’s output. Its position would be selected by putting on all the vehicle’s lights, starting the engine and moving the brush until the ammeter registered about +2amps, meaning you had enough output to power the lights and still feed a couple of amps to the battery.

The downside of this basic arrangement was that the battery was always being charged, whether it was necessary or not. That’s why people were always buying water to top up their batteries because it would boil away. So they put a switch in the live circuit – turn it on and the dynamo would charge the battery, turn it off and the charging would stop. (Cars had magnetos at the time which produced the power needed to run the engine when it was spinning, so they only needed the battery to power and run the ancillaries.)