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Bobble

Alternator Problems

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I am hoping that one of you electrical gurus will be able to help me with a problem getting my alternator to charge.  Before anyone simply states "replace it", I've tried that.

Following an evening drive in the dark with instruments seemingly powered by Toch H lamps I decided to replace my instrument bulbs with LEDs.  Having read a post involving a TR6 I retained the old bulb for the ignition light.  I tested the bulbs (having eventually switching on the panel dimmer switch) and everything worked fine.  However, the alternator was not charging the battery and having checked the circuit using all the normal tests my mechanical genius at Amrest Classics decided everything was fine so the alternator must be faulty.

About five years ago I replaced the old generator with an alternator kit from TRGB.  I contacted them and was told that they now supplied a different alternator due to issues with the original part manufactured in India.  I purchased and fitted the new unit with the same result - no charge.  This could be a complete coincidence (I'm sceptical) or I may have been supplied with a rogue alternator - TRGB say that they have experienced no problems with this unit.  One small point - the alternator came in a black box with a stick on label suggesting that it was a Lucas unit but this was onviously not the case although I am not suggesting that this is the problem.  I suspect that there may be some other fault relating to the fitting of LED lighting.

Any advice would be gratefully received.

Thank you

Bob

PS  The battery is fine having retained over 12 volts despite travelling around 20 miles without proper charge - the ignition light almost (but no quite) goes out when the engine is running.

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Current is needed through the ignition lamp to start the alternator  as you have recognised Bob but you say you have retained a bulb so that should be OK.

However -  I do recall some problems in the past where the ignition and oil-pressure warning bulbs have been inadvertently swapped over in the holders without the owner realising. Could that possibly be your problem i.e. the bulb you have retained is actually the oil pressure one not the ignition?

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That would be the indicator bulb (green lens) - there is no oil pressure bulb.

 

Make sure that the engine is earthed adequately.

Is the ignition light on permanently or off permanently.

The LED's should make no difference. but you could pull the 'Red' fuse to isolate them.

 

 

Roger

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Hi Bob, - Stick the ‘old generator’ back on...

So long as you retained the original dynamo, suggest put it back as manufacturer intended.... Mine is all original as left factory and never given any grief in40+ years of use, abuse and neglect........ Don’t think you will find many posts on here (or anywhere further) of owners having issues with the original set-up compared to all the woes and knock-on challenges of ‘upgrading’ with substandard after market poorly manufactured .. (carefully choose your own word here)...

 

Just my tuppence worth

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If you have a voltmeter, do some simple tests:

With engine running what voltage is on the main O/P of the alternator, & what voltage is on field connection.

(& report back !)

Bob.

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Wow!  Quick responses, thank you.

RobH - definitely have the correct bulbs in the appropriate holders but thanks.

RogerH - I think Rob means the back light for the ammeter.  Incidently the ammeter is new but seems to be working as it should.  Will definitely check all earths - good point.  The ignition light doesn't go out completely with the engine running - there is still a faint glow.  What is the "red" fuse?  Do you mean the permanent live?  I only have two terminals on the fuse box and the permanent live (not requiring ignition) seems to only operate the lights.  I will certainly try your suggestions - thank you.

Tony - I'd rather not go back to a dynamo but you have a good point.

Thank you for responses so far.  TRGB are sending me a new alternator but I'm not holding my breath on that being the problem.

Bob

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Lebro

Alternator is off the car at the moment.  We checked all voltages and there was no increase with the engine running.  Ammeter shows slight discharge.  All wiring checked out OK with everything pointing to the alternator but ......

I'll definitely get back to you when I fit another ammeter.  It's arriving on Tuesday.

Bob

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Hi Bob

Now you have the alternator removed you can check voltages at the connection plug . You should have constant 12v at  the large terminal and only 12v with ignition on

at the small terminal (ignition light feed ). If as you say the ignition light is on dimly then that suggests a diode fault within the alternator it self.   

Chris

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If your next new alternator also fails to work Bob, I suggest you connect a dashboard type bulb between 12v and the small spade terminal on the alternator and see if that wakes it up. If it does there is something wrong with the ignition bulb circuit.

 

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Thanks Rob and Chris - I'll re-visit the issue once the wind subsides!

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Hello Phil

No.  There has been no change - it has always been negative earth  as far as I am aware.

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Chris

I did your suggested checks this morning.

Results:   12.7v from battery;   12v from small terminal with ignition on;   Variable between 8 and 11 volts on large terminal with ignition off - this seems to indicate a poor connection somewhere - what do you think?

Worth bearing in mind that I fitted a new ammeter at the time of changing the bulbs.  Original ammeter had three wires utilising two large terminals and a small on the ammeter with one large and the small sharing a connection.  The new ammeter only had two large terminals but I soldered the small and a large together on one terminal to give identical connections to the original.

Any advice would be gratefully received.

Thank you

Bob.

 

Rob

Your suggestion also seems to be a possibility - any idea where the fault may be?

       

Edited by Bobble

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A question re those voltage readings - there are two large spade terminals on the alternator and some wiring looms have two thinner power cables instead of one thick one - is that the case with yours?.  

The large terminal(s) should connect direct to the battery via the ammeter, but with the small current drawn by your voltmeter the full battery voltage should be seen on that terminal all the time. It certainly shouldn't vary as you say it does and it should be 12.7 the same as the battery.  

I think you should check the ammeter connections. 

If they look OK then measure the voltage to earth at each of its terminals. The readings should be the same, if not suspect a fault in the ammeter. 

 

Edited by RobH

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Hi Bob, firstly check the ignition warning light holder is properly earthed, secondly do you still have your original ammeter, if so try that as that's about the only other part you've changed that could cause the problem because if wiring is as standard all the power on a 4A goes through the ammeter. 

Chris 

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Chris and Rob

Thanks for your help - I am beginning to think that the ammeter may be causing the problem (in which case I owe an apology to TRGB re their new alternator).  Basically I think that I have to go back to the beginning, remove the speedo to get at the ammeter and ignition light before checking all connections and take new readings at various points.  Not a job for today - it's too cold and I have no room to move in the garage.

Incidentally, a reading at the junction that used to be the voltage regulator is sound but drops to 11.5 volts at the fuse box (ignition terminal).

I appreciate you help so far.

Bob

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Bridge the ammeter connections with a piece of wire, so it's not in circuit. If that makes no difference then you have a bad connection somewhere else.

Pete

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Bob

the voltage at the alternator large wire should be battery voltage. Go back to the beginning of this feed wire which should be at the starter solenoid located next to the battery

and work forward from here which will be the ammeter across here then to the connections at the old voltage regulator. hope this makes sense and you come across a dodgy connection

Chris 

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I would argue that the main feed wire from the alternator should NOT go to the solenoid, but should connect to the load (non battery) side of the ammeter.

Otherwise you will never see the ammeter reading a charge.

Bob.

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Yes that is right of course Bob.

However I think Chris's  meaning was to start the investigation at the feed point to the battery side of the ammeter and work downstream from there checking in turn all the connections until reaching the alternator plug.

Personally I would suggest Bob pays particularly close attention to the connection which he tells us he re-soldered. 

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It is easy to stuff an alternator by removing the connection to the battery while the engine is running. One of the diodes will blow in milli seconds causing the ignition light to glow faintly when re connected. 

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Known in the EMC testing world as a "Load Dump"

Bob.

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Original old Dynamo, heavy and over engineered but still...albeit occasionally only just about... always reliably doing what it was made for and never a ‘Load Dump’.

 

Just saying....

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Dynamos are fine if you don't go out at night, I prefer to see the corner as I take my foot off the accelerator, had an alternator for 15 years now and wouldn't go back, Andrew

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Not knocking Alternators, but in the past 15 years LED lighting has come on leaps and bounds, and if all the bulbs except maybe the headlights are changed to LED then a Dynamo will cope just fine.

Of course you can always change the headlights to LED as well, plenty of posts on that on the forum.

As has been stated already it's only at night (ie when lights are needed) that the Dynamo comes into question at all. It's a plus/plus scenario to take the LED route as this reduces the electrical load on the whole loom.

Also don't forget to spec the largest capacity battery that will physically fit, Bosch do a good 74amp/hr one. And  replace all those corroded bullit connectors to ensure those Volts reach their final destination.

Chris 

Edited by ChrisR-4A
Info added

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