The 'E' Type Forum

Hi guys, My series 2 voltage gauge ,when starting, only reads to 12 volts. It will jump to 14 volts if I rev the engine over 3000 RPM’s and stay there unless I shut the engine down. The battery reads 12.87 volts at rest and only increases to over 14 volts while running if I again increase the RPM’s over 3000. The car does not have the original voltage regulator but has been upgraded. I removed the negative cable while the engine was running and it continued to run. Apparently the alternator is not producing enough volts to maintain the battery unless it’s “kicked-in” to a higher RPM? Any ideas or suggestions would be appreciated. Thanks, Allen

What alternator/regulator has your car been upgraded with? If it’s a more conventional system than the original Lucas 11ac with 4tr & 3aw, then does the warning light work? Most systems need a 12v feed through the warning light circuit to excite the alternator and get it charging, but will self excite at high enough revs. If you still have the Lucas 11ac with the 4tr regulator and 3aw warning light relay, then ignore the above.

Also, it’s a really bad idea to disconnect the battery whilst the engine is running, this can damage the alternator.

All of what Tom says is correct.
Another test you can do is to start engine and add load by turning on the lights wipers etc . See if the charge light comes on - and goes off by revving the motor. The old alternators though better than dynamo's at low speed charging are not as good as modern units which charge from 600-700 rpm or idle speed. Another thing to be aware of is the modern alternator has better voltage regulation and will not let the voltage get much above battery open circuit value - exitation is more finely adjusted. Old alternators would get up to 15v with higher engine speeds.
Let us know what alternator you are using.

Barrie