Flickering lights

[Les Pettitt]

Hi All,

I posted this topic on the TR6 forum but it has been suggested I post here to get a wider audience and maybe someone can help.

Briefly, my cubby box light, interior lights and headlamps flicker (pulse) at a rate of 1-2 times per second when the engine is running. The frequency does not appear to change with increasing revs.

If I remove the fan belt and run the engine for a short time there is no flicker.

If I run the engine with the alternator connected and put a bulb across my brand new battery there is no flicker.

But if I connect the bulb to the fuse box brown wire from the alternator then the flicker is back. An analogue meter shows a fluctuation of only 0.5 volts but the pulsing of a bulb is noticeable.

Is there anthing else I can try before I buy a new alternator?

Thanks

Les

 

[RobH]

See my reply on your original thread Les.  If you have done all the suggested tests (including the one from NTC) we have just about covered all the possibilities.  

An alternative to just buying a new alternator is to take yours to an automotive electrician to have it tested.

[Lebro]

If a bulb connected directly across the battery does not flicker when engine & alternator are working, then that suggests to me a bad connection between alternator & battery. Do you have an ammeter ? if so check those connections.

Bob.

[Les Pettitt]

Hi Bob,

No ammeter as it is a CR car.

I'll try pulling out the alternator connections on the main positive battery lead and see if that makes any difference.

Thanks for the suggestion.

Rob, good idea, I'll see if I can find a local automotive electrician.

Regards

Les

[Les Pettitt]

Hi Bob,

Blimey, that was hard. Those four large spade connectors in the battery positive lead are really tight to get in and out.

All looked very clean (I had a new loom in 2018) and has made no difference.

Apologies to RobH who had suggested this previously but I just missed it out.

I have also taken the plug out the alternator and pushed it back in. Again all looked fine.

I think my best bet now is to find someone to test my alternator. Either it will be the culprit or can be eliminated.

I have spent so much time on this.

Thanks

Les

[Les Pettitt]

Hi All,

Thinking about this overnight, the best way to check whether it is the alternator or wiring at fault would be to pull the three pin plug off the alternator and then test with a bulb each of the three terminals.

However, I understand I shouldn't run the alternator with the wiring disconnected or it may cause permanent damage.

Is there any way round this? (apart from an auto electrician)

Regards

Les

 

[RobH]

Alternators started to be used in the early days of semiconductors, when it was difficult to make decent high-current diodes (at the prices that car-makers would pay). Also the regulator circuits sometimes used the battery as a voltage reference. That means an alternator being run without being connected to anything could ramp its output voltage to maximum, which would destroy the diodes.  Hence the accepted wisdom not to do it.

Modern alternators are probably not at risk of this - but since many are still built down to a price by after-market manufacturers in the far East, who knows for sure?  

I don't know what you mean by testing with a bulb at all three terminals Les. The two large output terminals are usually joined together inside the alt and the third connection is for the warning lamp so putting a bulb on that won't tell you much. Also it is likely it may not 'start up' without the current normally coming from the ignition bulb anyway, so you would have to rig some supply for that else start-up would depend on whether there is any residual magnetism in the field.  

Unless you really know what you are doing I can't see this will tell you anything. 

 

Edited June 8, 2021 by RobH

[Les Pettitt]

Hi Rob,

Thanks for the info. I was going to put a bulb between earth and each of the three terminals in turn to see if it flickered.

I didn't know the two large ones were joined or the small one is for the warning lamp.

The weirdest thing is that with all this messing about pulling and replacing connectors and changing the fuse box my flicker has been reduced to more of a pulse so the lights don't dim as much as they did last week.

I have now run out of ideas and will try to find a local auto electrician so that I can know for sure whether or not the alternator is the culprit.

Thanks for all your help. Everyone must be bored rigid with this topic by now.

Les

[RobH]

16 minutes ago, Les Pettitt said:

The weirdest thing is that with all this messing about pulling and replacing connectors and changing the fuse box my flicker has been reduced to more of a pulse so the lights don't dim as much as they did last week.

...which tends to suggest some of this is related to iffy electrical joints.  It's  not unexpected at all that disturbing things will clean up contacts.  The alternator earths back to the engine through its bolt connections so perhaps disturbing those might help too, though you probably did that to take the fan belt off.  Also what is the engine block earth connection like?  I know you said the car cranks over OK but it might still be worth cleaning that up too while you are at it.   

[Les Pettitt]

Hi Rob,

Yes, I had the alternator top bolt off a couple of times and it all looks pretty clean.

The main earth is via a hidden battery cut off switch using 170 amp battery cable to the switch from the battery and from the switch to the body.

There is then a braided earth strap ( for Massey Ferguson 135 ) from the body to the engine.

All these cables are much meatier than the original earth strap.

If the general earth was at fault would it not still show up when running the engine without the fan belt?

A faulty earth on the alternator itself would seem to fit in better with my symptoms but that seems unlikely.

And yes the car cranks and starts better than it has ever done.

Very grateful for all the time and trouble you have spent on this.

Regards

Les

[Les Pettitt]

Hi All,

 

Thought I would post the reply I got from the alternator supplier. I think a visit would settle it one way or the other.

Hi Les,

Most alternator faults are with them either not charging, or in some cases over charging.

Lights pulsing/flickering could also be a problem with the unit, but can also be due to low engine speed (at idle)

or even bad earths (also more visible at low speeds) as well as some other factors.

It would be interesting to see what readings were obtained from a voltmeter.

If the unit was off the vehicle we could test it on the test bench and confirm the fault.

This type of unit we don’t normally repair anymore as the repair price can be near the cost of a new unit.

This unit we would sell at £65+vat and would normally have to order in for next day.

 

Andy

A&P ELECTRONICS

[Les Pettitt]

Hi All,

Problem solved.

I spent another couple of hours checking all electrical connections but it made no difference.

I removed the alternator and found to my surprise that my restorer must have dropped it as the bottom lug at the front had been broken off and welded back on.

I'm not sure welding would do the internals much good.

I took it to a local alternator repair shop and was told straight away that it was faulty as it was generating 14.8 volts increasing to over 15 volts under load.

It should be in the range 14.2 to 14.3 volts.

I bought a recondioned alternator on the spot , fitted it, and all ok now. Rock steady lights, no flicker or pulsing at all.

Regards

Les

 

[Mk2 Chopper]

Great result Les, got there in the end!

Gareth