Recently fitted 4 new halogen lights to Helen dolly.
Volt metre not keeping up to 13 and a half 14. Think it's the alternator rectifier that is faulty. Thought of buying a new alternator but what is a suitable amp for the car with the new headlights? 35? 50? 60? Any advice please!
I've added up the total current that could potentially have to be supplied by a Dolomite alternator. And I was quite surprised.
Here are some numbers from the Sprint workshop manual.
Headlamp (dipped) 2 x 60 W = 120W = 10A( Exceeded by main beam)
Outer 75 W Lucas units x2 + 60W x2 = 270W = 21A
Sidelights and tail lights number plate lights. = 28W = 2.5A (Rounded)
Heated rear window 10A
Windscreen wiper 2A
Heater blower 4A (estimate)
Indicators 1-side 21W x2 +5W =47W =2A rounded up.
Gauge pilot lights 19W = 2A rounded up
Radio 1A ( estimate)
Total = 44.5 A potential maximum.
So Triumph in fitting a 35A alternator are relying on not everything being on at the same time.
So a 50 A alternator would be good. A 60A one better. And with the larger brushes in the 60A unit with the better rated components there would be improved reliability.
In addition to Mart's notes on alternator testing there is a useful section on testing the alternator in the Sprint manual.
As he says, don't rely on the dashboard voltmeter. It is for indication only. The important voltage measurement is the voltage straight across the battery, so use a dvm.
There are 3 tests to be done.
Start the engine and run till it is hot.
* With the main electrics off the IGN light should be OFF at 660rpm engine speed.
* At 2,450 engine rpm the voltage across the battery should be 13.6 to 14.4 V
( If this is wrong suspect the regulator, but it can also be major rectifier pack failure or windings.)
* Turn the electrics on to give approx; 35A. ( Main beam plus HRW is close ). Set the engine to 2,450 rpm.
For the 18ACR unit there should be 14V nominal as above.
( If this is wrong suspect rectifier pack or windings or field brushes.)
( The manual actually does this the other way, setting the current to give 14V nominal output ).
* For a 60A unit set all the electrics on and look for the nominal voltage of 14.0V +/- 400mV.
Make a mental note of what the dvm reads compared with the dashboard voltmeter for future reference. The reason for the dashboard voltmeter reading low is due to voltage drops in the wiring.