TR5 - Alternator Charging Conundrum

[Jim F]

I'd welcome the forum's advice on a problem I'm having with my charging system. Firstly we're dealing with a TR5 that's been running on alternators for the last couple of decades and its fitted with a dashboard ammeter.

 

The problem is the ignition light is illuminated after the engine is fires up. Not an uncommon problem so I went out and did a couple of things - I had the 'faulty' alternator repaired and I bought a new alternator as well. But in both cases when I fitted the repaired or new alternator the problem persisted - the ignition light stay on after the engine was fired up. So I could conclude that i've still got a bad alternator but here's the diagnostics that I find confusing and I'd appreciate your help.

 

Battery voltage across the terminals before I fire up the engine is 12.82 volts. ( 24 hours since car last used)

Once I fire up the engine:

Ammeter indicates that there's a positive flow of current. Initially, once the engine is running. the ammeter deflects strongly to the positive then settles to a lower rate of + charge.

At 1000 rpm the voltage across the battery is 14.25 volts.

At 1500 rpm the voltage across the battery is 14.3

Headlights dim as rpm drops and brighten when I rev the engine just as you'd expect.

So I'd conclude the alternator(s) are functioning (and I've had both alternators checked by an alternator repair specialist and he tells me both are working fine).

 

Once I power down the engine the battery voltage is 13.1

 

So both the voltage increase and the reaction of the ammeter tells me that the alternator (both of them) are generating a charge.

 

I've even replaced the ignition bulb and that didn't cure the problem.

 

This is the first problem I've had with the charging system in a decade and nothing (other than the replacement of the alternator) has been changed over the last couple of years.

 

Advice appreciated and thanks for the help.

Jim

 

 

 

[AndrewP]

Jim,

 

Not so sure about the TR5, but on the early TR6's you need to make sure you have the oil pressure and charging bulbs the right way round (they both have the same holder, and so its very easy to swap them over when refitting).

 

Easiest way to check is to ground out the oil pressure switch when the engine if off and ignition on. That should illuminate the oil pressure lamp.

 

Of course, this also isn't a good scenario as you could be running low oil pressure, but it could be something as simple as a fault pressure sender or even just a broken wire that's touching the engine block.

 

All the steps you've detailed above seem to indicate that its working. The only next logical step would be to try another battery.

[John L]

Which alternator do you have?, if its a 5, that hasn't been adapted to the newer ACR alternators it will have a different control box on the l/h wing, rather than one that is built into the alternator itself on the later ones.

John

[RobH]

Well the good thing is that your readings show the alternator is charging OK and behaving exactly as it should Jim and that the battery is probably all right too. Supposing that everything once worked properly and that this is not a confusion of regulators or lamps as John and Andrew suggest, its possible that the lamp circuit may have developed a short to earth somewhere on the alternator side. The other side of the lamp is connected to the battery via the ignition switch so a short on the alternator side will keep it permanently lit - definitely indicated if the bulb brightness stays the same when you rev.

 

If you stil have the the external-regulator alternator there may be a fault in the regulator unit which keeps the + terminal at earth, unless you had that checked out at the same time as the alternator of course.

 

Rob

[RogerH]

Hi Jim,

the Ig lamp is fed from the battery via the ammeter and returns to the alternator via its external control box.

 

When the Alt and Battery are apprx equal (car running) the lamp goes out.

In your case something is not equal.

have a look here http://www.advanceautowire.com/tr2506.pdf

 

The TR250 should be about the same as a TR5 - from the Ig switch the white wire also goes through a fuse to some other areas - remove the fuse with the engine running to eliminate this part. If the Ig lamp goes out then you have an earthed wire somewhere.

 

You could also pull the Brown/Blue (NU) wire from the light switch junction.

 

Otherwise you are looking at the control box.

 

Roger

Edited April 6, 2015 by RogerH

[Lebro]

+1 but keeping out of this one, as no experience with external regulators !

 

Bob.

[john.r.davies]

Check that you have a good earth for the engine (and Alternator).

I had this problem and took ages before I realised that there was no engine earth.

Now, I have a length of starter cable, from block to the battery earth point.

JOhn

[ctc77965o]

Hi Jim,

 

What type of alternator is it? A two wire type??

 

whatever it is, what colour are the orig wiring loom wires connected to it??

 

Is a control box still in-place? Are there any wires connected to it??

 

14.25 sounds a little high, should be 13.8 for a modern Alt charging lead acid (different for calcium, gel etc)

[Jim F]

Thanks for the feedback and sorry for the slow response.

The alternator has an internal regulator and its a replacement I purchased several years ago (the fiesta alternator upgrade), that used to be available in the US. It has the 3 blade connector but I don't recall the make - I'm on the road at the minute so i can't provide that info.

 

There is a good earth strap in place and there are no other electrical system issues.

 

Just to clarify the vehicle is a TR5, one of few in the US, and it still has the the Lucas PI system and it. Operates with the stock ammeter, (rather than a voltmeter). The wiring loom hasn't been a problem, (replaced a decade or so ago) and the vehicle is still right hand drive.

 

Anyway, back to alternators, thanks for the suggestions and keep them coming - it's going to be a straightforward fix once I find it!

 

Thx

Jim