How to update your Lucas Voltage Regulator

The older style metal case Lucas voltage regulators work using a bi-metal strip that warm as current flows through the coil of wire wrapped around it, this causes it to bend and break the connection, therefore causing it to cool and straighten, where the cycle starts again. This gives an average of 10 volts on the output. This however is affected by the surrounding temperature and as on the Coupé the demister pipe is quite nearby, I decide to modernise the circuit.

The 7810 voltage regulator IC is widely available for a less than a pound and it would be a case of just soldering on three wire, however I decide to fit it to the existing case.

Lucas regulator
Original Lucas Regulator

The Lucas voltage regulator as originally fitted to the car

Lucas regulator
Both Regulators side by side

Replacement 7810 along side for comparison, same job, more relable and a fraction of the size.

smith voltage regulator pins
regulator connection

The three connection on the Lucas regulator are marked; B-Battery Feed, I- Instrument Feed, E- Earth.

lm7810 pins
lm7810 connection

The 7810 has the following connections from left to right, Voltage in, Ground or Earth, Voltage out, the mounting tag is also ground.

Lucas regulator
Top case removed

The first step was to remove the top of the metal case, this I found easier with a pair of wire cutters to lever the small folded lip straight.

Lucas regulator
Bimetal switch

This shows the bimetal switching arrangement and the heater coil.

This is the meter output show on a moving coil meter.

Lucas regulator
Connections

This was cut off allowing a small connection to be left, the earth connection was twisted slightly to allow more room to solder on the wires. Each connection was given a quick sand to allow a good surface to tin with solder.

Lucas regulator
TS7810 Regulator IC

The 7810 then had three wires attached and covered with some heatshrink.

Lucas regulator
Wire connections

These wires were then soldered onto the tabs inside the case. These were then covered with some tape to prevent the tab on the regulator touching them.

Lucas regulator
Completed regulator

The case was then crimped back together using a set of mole grips.