The Triumph Dolomite Club - Discussion Forum

Last year in July I changed the alternator with a new one on my 1850.
Recently the voltage gauge catches my eye. Directly after starting the voltage gauge takes some time to raise to a healthy 13 Volts. After a couple of miles it catches up. It's not just the gauge, the OD can't be switched on until the voltage reached the desired values. When I've to stop during the trip, say at traffic lights, the reading drops again and sticks at 10~11 Volts.
Can someone point me in the right direction: what does this mean, what's on its way out?

They might not be related.....
Bit of a pain, but....
Carry a meter.
On start-up measure the volts across the battery.
A couple of miles later, same again, you get the picture.
I would think 13 volts is too low, but don't trust the car's voltmeter.

The overdrive might just need the oil to heat up.....

I second what Bill said about not trusting the in-car voltmeter. Better to measure the voltage across the battery terminals with a multimeter for a more accurate reading.

Alright, I measured the battery poles:

engine off: 12,4 V
engine just started, idling with choke so about 1500 rpm: 12,5 V
engine a bit revved, 2500 rpm: 12,5 V
engine revved a bit more. 3000 rpm: 14,5 V
back on choke idling: 14,5 V
idling, 800 rpm: 14,5 V

So it takes a while to climb up. When the 14,5 V is reached it stays there, even when rpm's are dropping.
(although I had a trip last week where the voltage dropped after some minutes idling, when I was out of the car)

In car voltmeter seems inaccurate regarding actual values, but is following the increase or decrease in voltage.

What does these symptoms tell?

Could be a problem with the machine sensing.

I think Jon had something similar.

Engine not running you should have 12.6V, so 12.4V is a bit low. As far as I know you should have the 14.5V (or there abouts) even at idle.

Alternators shouldn't be idle/rev sensitive, something's not right. 14.5 volts ish all the time, irrespective of engine speed. Dodgy alternator is my guess, possibly the regulator knackered? Or sticking/worn brushes?

Its lost the sensing bit so wakes up at 3000 rpm.
Mine was the same. Its one of the diodes that's blown....

I had a spare so swapped it...problem solved.
There is a lot on youtube that shows how to change lucas acr regulators etc...

Jonners

Thanks guys, I'll check it later this week.

Hello Henk, Sorry about the late reply and it was jolly good meeting up at Stoneleigh may I say ! ( I was the one with the MGB btw.).
There is one other possibility for the slow increase of voltage. Is the ignition warning light working O.K. or has it been swapped for a low-current LED bulb ?
The reason this will give a slow increase of alternator voltage is that the current that flows through the ignition warning light provides some initial alternator field current during start-up. If this current isn't present then the alternator relies on the residual magnetic field in the field winding to get the current flowing. Which can take some time to establish itself.
There is a useful circuit diagram on page 86-11 of the Sprint workshop manual that explains this.
HTH.
Cheers for now,
Tony.