Triumph Repair: TR4A Generator Options, alternator pulley, drive pulley

Question
Hi Howard,

My TR4A is running the original generator with no problems or issues other than insufficient output at idle. This mostly means the gauges all die, the headlights are very dim and (most importantly) the turn signals do not function when idling at a stop sign.

It is not big deal and I was considering upgrading to an alternator in the future when this morning it dawned on me, why couldn't I simply install a smaller drive pulley on the original alternator (thus, boosting output at idle)?

If over-revving the generator is a concern, the car redlines at 5000 RPM but, I very rarely take the engine up to 4000 RPM - mostly shifting in the 2500 - 3000 range.

So, would a smaller generator pulley do the trick?

Thanks

Bob

Answer
Hi Bob,
That is a catch 22 as when you change the ratio of the drive you make the generator spin faster at idle but when you turn the higher RPM of highway cruise and acceleration you will destroy the armature as it can't take a high RPM as it is. I have had customers come to me with destroyed armatures just from them running the car at speed too much.
The problems you are experiencing are why the alternator was the replacement. An alternator can produce a higher charge rate at a lower RPM than a comparable generator can. But keep in mind even an alternator must be correctly matched to the car and battery. For example a 75 Dodge van with air etc will run a battery down at night in city traffic in the rain as the set were not matched correctly. So you still need to carefully match the alternator, pulley size, battery and what electrical loads you put on the system.
A "Deep charge battery" can also go a long way in solving idle charge rate problems.
Sorry that there is not a simple answer but if there were, some car manufacture would have tried it.
Howard