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MG MGA - Higher coil voltage for starting

In warm countries like mine old sports cars usually start with a short use of the starter, but what about in very cold countries? I am sure you people drive your MGA's in freezing conditions (?).
When the starter turns over a very cold engine for a longer than normal period there must be a considerable voltage drop at the coil, probably to 10 volts.
Has anyone tried the system used on Triumph cars? The have a 12 volt system but a 6 volt coil. This would normally overheat the coil and cause points and plug erosion.
The Triumph has a resistor in series so that the 12 volt battery supplies 6 volts to the coil when running.
However, whenever the starter is in use a lead directly from the starter cable to the coil supplies 12 volts to the coil. Now, even during long cranking by the starter, the 6 volt coil will get at least 10 volts. The result is easy starting.
This a simle fit.
Anyone in Australia (where this system is not necessary) want a Lucas 6 volt coil? I have half a dozen to get rid of for no charge.

Mick Anderson

I have to criticise my own idea. It works well on Triumphs, but there is a problem if you try to fit it to the MGA.
On the MGA the power cable from the starter operating switch goes directly to the motor windings. The 6 volt battery supply (through the resistor) would share a coil terminal with any lead that would be connected to the starter cable. When the engine is running there would be 6 volts passed to the starter windings at all times.
The Triumph has a pre-engaged starter. When the starter switch is operated power goes to a solenoid mounted on the top of the starter. The solenoid moves a lever which engages the pinion gear with the flywheel ring gear. Only when the pinion gear is fully engaged is contact made with terminals on the starter to send power to the starter windings. At the same time it makes a contact which sends 12 volts to the coil. When the solenoid disengages (engine running), power from the common coil lead cannot run back to the starter windings.

And it seemed like a good idea at the time!!

Mick Anderson

Mick, If someone wanted to try this, it could easily be done with the addition of a small N/O relay. The coil of the relay would be wired to the starter-side of the starter switch. the contacts of the relay would be wired across the rsistor in series with the 6 volt coil.

While the starter switch was activated, the relay coil would be energized and the resistor would be shorted thru the relay contacts. Thos would feed 12V to the 6 Volt coil. When the car started and the starter-switch was released, the relay would return to its notmally open position and the resistor would be dropping the voltage to the coil at 6 volts.

Although I haven't tried this, it should work just fine if you feel the need to change the original system.

Chuck Schaefer

This thread was discussed on 12/05/2007

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