Interpreting the ammeter [again].

[Member 10617]

In previous posts, I received very helpful information and suggestions from you about my ignition light coming on when my car was idling (1100 rpms). Several of you suggested that the cut-out in my mechanical voltage regulator might have needed adjusting.

Rather than spend the time and money taking the car to a shop to have the cut-out adjusted (adjusting it is farily complicated for a novice like me), I ordered a Moss preadjusted and precleaned voltage regulator.

The preadjusted regulator arrived yesterday and I installed it this morning and took a test drive (30 degrees! No side curtains on!)

Here is what happened. The ignition light either no longer came on at idle or came on very, very faintly. So it appears that that problem (cut-out misadjustment?) may have been been solved.

After driving enough to fully recharge the battery, the ammeter stays on "0" while I am driving. That's good!

When I turn my lights on (Xenon lights installed), the ammeter will drop a little or stay at "0" as I am cruising along steadily (and increase as I rev up), but when I idle with the lights on, the ammeter needle falls to halfway between "0" and -30. It rises back above "0" when I get back underway. This is something new for me as the ammeter needle never fell so far before at idle with lights on.

The main question: Is all this normal, or is this a sign that the generator (which is new) is not able to support the lights?

I have read a lot about how a mechanical voltage regulator and an ammeter work, but I have never found anything that simply describes what I should be seeing on the ammeter when the car is working properly.

For all I know, everything may be working just fine now, but I'd rather not guess at it.

Your help, as usual, will be greatly appreciated!

 

[TR3driver]

That behavior is pretty much normal, Ed. The output ability of the generator falls way off at lower rpm even before the light comes on, so the battery has to supply the power to run the headlights. Lucas gives 4500 rpm (at the generator, roughly 3000 engine rpm) as "full charging rpm" where it should reach it's rated ability of 19 amps.

But "not able to support" depends on your driving habits. The generator was marginal by modern standards even with the stock 36 watt headlights. If your driving includes a lot of low speed, stop-and-go without some matching higher speed legs to recharge the battery, then you may find that the generator needs help, either in the form of external charging after a run or upgrading to an alternator. I forget where offhand, but one of the manuals even suggests using an external charger after a winter run (presumably to ensure the battery is charged enough to prevent freezing).

BTW, alternators suffer this same problem (low output at low rpm) but to a somewhat lesser extent.

 

[Member 10617]

Randall. Once more you have come to my rescue! Many warm thanks... on this very cold day!

The generator in my car was installed new about nine months ago, so with luck it is up to modern standards. My lights are Xenon, which draw a little less current than traditional lights.

But you are right about my driving habits. A lot of low speed, though not too much stop-and-go driving. Some "high speed" (50 mph) on the back roads of western Virginia, but rarely anything over 55 mph.

I think it was you who suggested that my problem might be with the adjustment of the cut-out relay in my voltage regulator. As I said, rather than tackle this myself, I wimped out and purchased a pre-adjusted, cleaned, and tested voltage regulator from Moss. Installing it (a simple job for most) was a major accomplishment for me. Thanks for the advice.

BTW, as you probably know, Moss says that "The regulator relay should be adjusted so that the points open at 13 to 14 volts. The cut-out relay should be adjusted so that the points open at 10 to 12 volts. We realize that these are not the specifications in the workshop manuals for cars equipped with these regulators. They are more conservative, and perfectly functional. Using these settings will minimize the chance of a problem with your new regulator and extend the life of your battery. Note that the settings for the relays in the workshop manual SHOULD NOT BE USED." .....I wonder if this has anything to do with the behavior of my regulator and the indication on the ammeter?

I read more and more of the advantages of an alternator (either with an internal or external voltage regulator). I'll ask my shop-guy about this the next time I take the car in.

 

[TR3driver]

.....I wonder if this has anything to do with the behavior of my regulator and the indication on the ammeter?

Seems likely to me. Setting the generator output even lower than Lucas recommended will reduce the strain on the generator (just like engines last longer if you never use full power), and reduce overcharging of the battery under sustained high speed driving (thereby prolonging battery life). But it also means the generator doesn't do as good a job of keeping the battery fully charged under adverse conditions (cold weather; headlights on; short, low speed trips).

But by "modern standards" I meant simply that people today expect a lot more from their cars than was considered "normal" in the 50's. Back then, it was considered normal to perform various sorts of maintenance on a regular basis (like charging the battery); today everyone expects to just dump fuel in the tank and drive. My point is that, no matter how well it is restored to "as new" condition, this is still a 1950's car, with all the limitations and foibles that were accepted then.

Or, to put it another way, there is a good reason they were supplied with a hand crank!

FWIW, I used to drive a TR3A year-round in a climate slightly colder than Lexington. It was only about 5 miles to work, not nearly far enough for the generator to recharge the battery. Converting to an alternator was one of the best things I ever did to that car! No more dead batteries, ever again.

Running the original generator on my project TR3 has really brought back the old days ... unfortunately not in a good way! :laugh: The only question now is whether I install the old Ford alternator from the 3A as a stop-gap, or go ahead with the 'mini' alternator.

 

[Member 10617]

In 1962, my '58 TR3 had a crank... and I am very glad it did. On a trip across country, part of the ring gear disintegrated (from abuse by former owner) and I had to start the car with the crank all the way from Chicago to New York and back to Arizona.

Since I have fussed with this voltage regulator and generator for about 9 months, and now that I have it working tolerably well, I think I'll just drive the car and not worry about it much any more. I'll try not to use my lights much (I don't drive at night) and I'll pick up the speed a bit... and hope for the best.

But I think an alternator is in my future.