Alternator help

[Barrington69]

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!

[Toledo Man]

Did you fit relays when you did your halogen conversion?

Original fitment was the Lucas 16ACR or 17ACR depending upon exact model. A higher rated alternator is worth getting.

[Carledo]

How does it charge with the lights off? If that is normal, then the alternator is probably OK in itself, just not man enough for modern extras.

The original 17ACR alternators were only 35 amps IIRC a quantum leap in performance over a dynamo which cannot put out more than 22 amps, but still no great shakes, these days the factors often ask if I want the 120 or 150 amp model for moderns.

Unless you have electric power steering fitted, 65 amps should be more than enough for a Dolomite.

Steve

[Barrington69]

I haven't fitted relays. But have been told one should. Next on the list.
The has an 18 acr Lucas alternator already. But if I replace it with same, but with 65amps will I do any damage To the wiring???
Thanks
Bb

[Toledo Man]

You really MUST fit those relays soonest. There's a good chance that your indicator stalk will burn out especially with the haolgen headlights. The relays take the load off the headlight wiring. You will be fine with an 18ACR alternator. I believe that this was what was specified on the police Dolomites.

[GTS290N]

Even with standard lamps you MUST fit relays asap! The stalk will burn out. Jeroen does a lovely conversion set for about 125 euros ish, I've fitted this to my 1850.

[Galileo]

You can get a drop in 70amp replacement for £50 from Mini Spares.

[Mad Mart]

Before shelling out for a new alternator I would establish if yours is charging ok. With the engine idling and all the electrics off, measure across the battery terminals with a multimeter. If you are seeing 14.5 Volts, or there abouts, then your alternator is charging correctly. The Voltmeters in our cars aren't the most accurate. If the alternator is at fault, a rectifier pack is only six quid and it's a fairly simple replacement, with a bit of soldering.

[MIG Wielder]

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.

HTH,
Tony.

[Galileo]

You divided by 12v for the battery voltage should that not be 14v for the running voltage? (innocent question, don't actually know).

[Jon Tilson]

Room temp ISA blah blah blah a lead acid accumulator is 13.2 Volts.

Ergo 12V is nominal....and the 13.6 to 14.2 is what the alternator puts out to charge it.

And it drops with temp. You can google it to find various graphs...

Jonners

[cliftyhanger]

But lets beclear. Halogen bulbs take no more current than the std type, so put no more load on swithes than what was already there.

However, fitting relays IS a very good idea, irrespective of bulb type. They take the load off the ancient switchgear, and reduce voltage drop to the bulbs, so they are brighter.

I just did the RBRR,so that entailed over 20 hours of headlights, much of it with main beam and spots (this is a toledo, so single headlights) and the rest with dipped plus driving lamps.
OK, no heated windows, and the heater motor was rarely used. Radio blaring out tunes incessantly (the Who at 3am? seems normal!) and all this on a baby denso 40A alternator. Our current draw was circa 25A. But there is a caveat here. We rarely had to start the car, well, only every 2-3 hours, and so starting drain was not something to worry about. If a car is used for short journeys I would be a little more concerned (actually, the car is a daily town car at the moment, and often is)

My choice would be a 40-60A version, all will be fine. My main bitof advice would be to add an extra, nice thick wire from the alternator to the solenoid connection or direct to battery positive. The old cable was designed for the old 25ish amp alternators, and you don't want to overload it if the battery is rather drained.