TR2/3/3A Alternator not charging?

[karls59tr]

I installed the alternator kit about a year ago and haven't had any problems till now. I went to start the car but it seems that the battery was weak. It started but the voltmeter showed a discharge. Since the car had been sitting for a few weeks I figured I'd drive it and charge up the battery. Driving along the gauge showed it wasn't charging? Red ignition light came on. I returned home in case I ended up somewhere with a no start condition. Seeing as how this is an alternator conversion I'm not sure where to start to track down the problem. I'm going to trickle charge the battery tonight so I can tackle the issue in the morning. There was about 1/2" play in the belt. Couple of days ago I had swapped out the cap,points and condensor into a TR4A for testing purposes then put everything back the way it was. But I can't think why that would cause an issue as I took the 3 for a fast run after reinstalling with no issues. What's the best way to do some simple tests on the alternator?

 

[dklawson]

Start as you have proposed by recharging the battery. After disconnecting the charger, allow the car to sit for a half hour or so. That will allow the battery to drop to its at rest voltage. Then measure the battery voltage using a multimeter. Start the engine and measure the battery voltage again. Obviously look at the charge warning light and note if it is on or off. You would like to see a 1 to 1.5V increase in voltage across the battery if the alternator is working.

Now take your multimeter to the alternator. Switch the meter to measure AC volts on a low scale. Connect the meter between output terminal (big brown wires) of the alternator and ground. Measure at the alternator, not the battery. If you see more than 100 millivolts AC, that suggests a failing alternator diode.

However, you asked the EASIEST method to test the alternator. The easiest method is to remove the alternator and take it to a local auto parts store. Most will offer free bench tests of alternators on the assumption you will buy a replacement from them if it is defective.

 

[TR3driver]

Easier yet IMO to drive to the store (on your freshlyl charged battery) and let them test it on the car.

But if your voltmeter isn't coming up, the chances are very good the alternator isn't doing it's thing. I'd make the usual checks (belt tight, wiring connected and in good condition, etc), then replace it.