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angelfj

Bloody Ignition Light

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Unless you have a failure in your wiring, which is most unlikely, it is down to one of two things.

 

First some explanation- the ignition light is driven by the voltage between the dynamo output and the battery voltage. When you first switch on with engine stopped it is lit by the 12 volts at the battery returning through the bulb to the dynamo (currently at zero volts). As you start then rev up the dynamo volts rise, the light gets dimmer as the dynamo volts get to 12, usually around 1200 rpm. At this point the cutout in the control box operates and connects the the dynamo to the battery. The dynamo and the battery being both at 12 volts the light is out.

 

Likely fault one. The dynamo has de- magnetised from long non use. This is rectified by giving it a quick 12 volts on its windings. The easy way to do this is to manually flip the cutout contacts closed then open again. You get at the cutout by taking the cover off the control box. You will see two bobbins of wire. The one on the right as you look at it has contacts at the top. These are the cutout contacts. With the battery normally installed on the car give the end on the bobbin a light press to cause the contacts to close then release. There will be a bit of sparking- don't be concerned. This should have re- magnetised the dynamo and you should now get back normal operation. (This is probably what happened to Don some years ago.)

 

Possible fault two. The cuttout contacts are dirty. Clean them as described above, particularly if there was no sparking when you did the action above. A good indication of this fault is if the ignition light goes out as you rev up to around 1200 rpm then lights again if you rev higher.

 

The control boxes are incredibly robust as long as you don't go adjusting screws or bending the fixed contacts.

 

Good luck.

 

Phil

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Lucas reckoned that they made £35.00 every time someone took the cover off the control box.

 

Good luck,

 

Richard

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+1 for Phil's explanation. you may have to pull the cutout contact to release it after "flashing" the dynamo - the contacts sometimes stick closed.

I would give the cutout, & regulator contacts a quick clean while you are in there. Nothing to fear inside the reg box, just don't adjust anything without a good moving coil meter, & a set of instructions (as given in the workshop manual).

 

Bob.

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Hello all, from partly sunny, hot and humid Solomon's Island, Maryland, USA. Here at our 2015 TRA Convention I encountered just as many opinions regarding the charging system. More in a moment.

 

Yesterday, we had a cats and dogs thunder shower late in the afternoon. We were very careful to permit some rain this week in order that your own Mr. John Saunders would feel at home. John doesn't say too much, but once you get him started we find that he is a wealth of knowledge in all things TR. For those not familiar, there are two main TR clubs in the USA, The Triumph Register of America (TRA) catering to the side screen cars + TR4 and The Vintage Triumph Register (VTR) which cover all the TR range + Spit and GT6. TR4's were added to TRA a few years ago, although many of us think they look funny. They are allowed because except for an Italian body shell, underneath they're really a TR3B! :)

 

Now, back to my 3A. My mate Brian, the young man who restored the Grey Lady came to the rescue after dinner on Tuesday. I had already discovered the cause for the crazy findings reported in the first post. It appears that my dynamo had lost all of it's residual magnetism. During one of the Lucas recommended tests, they have you disconnect the leads from the dynamo, and then measure the voltage from terminal "D" to earth. There should be maybe 1.5 - 3 volts at a high idle. I measured approximately 0.6. This made me very depressed and thoughts about trip cancellation started floating through my brain. However, it just didn't make sense. I thought I should check the field windings for continuity. I measured about 6 ohms from terminal "F" to earth which is about right. I repeated the first test, but first I "flashed" the field. I just took a bit of wire and briefly connected the field terminal of the dynamo and battery positive. The other tests indicated a good dynamo but perhaps a control box that needed adjustment. Those adjustments sorted and I was soon to be headed South!

 

After reflection, I still don't know why the dynamo needed to be flashed, because I stored the car over the winter, just like I always have.

 

Cheers,

 

Frank

 

P.S. - I'll post some photos of this event in a few days.

 

 

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Frank - good to know that all is well with your charging circuitry and that you can make the trip.

 

John Saunders: a quiet and reserved fellow, but, as you say, once the cork is out of the bottle, there's no stopping him and he is a mine of information.

 

Ian Cornish

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Frank,

 

Good to hear that you are now running OK.

 

The magnetic material in your dynamo is so called "soft" iron. This means that it does not really remained magnetised indefinitely. (If it did remain magnetism permanently the control box would not be able to control its output, so this is deliberate, not a shortfall in the design). If you leave the dynamo long enough in a non magnetic environment it will gradually lose its magnetism. Strong mechanical shocks can also affect the retained magnetism. So, it's nothing you did (unless you dropped the dynamo on the floor) and it happens all the time.

On most occasions there is a little magnetism remaining and when the dynamo spins this is enough to produce a small output voltage which the control box then routes back to the field winding, generating a bit more magnetism,and so on until the dynamo comes up to full voltage. If the dynamo is left unused for long enough it will lose sufficient magnetism that it won't generate, though this is a rare event. Practically every charging system worked this way until alternators came along- it's not a TR or even a Lucas issue. See my post above on how to easily resolve the situation should it occur.

 

It's the same old story- old cars respond best to being used.

 

Phil

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