Ignition warning light

[bob_rich]

Hi All

One possible explanation for the ignition light stays on then a blip of the engine to 1500rpm and it goes out then (maybe) stays out may be to do with the resistance of the bulb. Filament bulbs have a cold to hot resistance ratio of frequently more than 8 so different bulbs of different manufacture may show some significant variation.

the current to feed, and initially power the regulator, in the alternator flows through the bulb and so once it goes out the regulator may see a different series resistance depending upon bulb tolerance.

A check to confirm if this could be it would be to change the bulb from say a 2W to a 3W and see how it responds

As many other posts say Good slip rings and sound connections are also very important and frequenctly the cause of charging problems

Hope this helps

Bob

[Plus 2]

Hi All

One possible explanation for the ignition light stays on then a blip of the engine to 1500rpm and it goes out then (maybe) stays out may be to do with the resistance of the bulb. Filament bulbs have a cold to hot resistance ratio of frequently more than 8 so different bulbs of different manufacture may show some significant variation.

the current to feed, and initially power the regulator, in the alternator flows through the bulb and so once it goes out the regulator may see a different series resistance depending upon bulb tolerance.

A check to confirm if this could be it would be to change the bulb from say a 2W to a 3W and see how it responds

As many other posts say Good slip rings and sound connections are also very important and frequenctly the cause of charging problems

Hope this helps

Bob

Bob,

Your theory here is absolutely correct increasing the lamp wattage from 2 to 3 watts will increase the amperage as the filament resistance will be lower in a higher watt lamp/bulb.

That said I would just replace the lamp for the standard specification initially as the contacts in the bulbholder and bulb itself do get oxidised along with the Lucar connectors so need to be cleaned anyway.

The oxidisation on any contacts in the circuit can significantly increase the line resistance which here is in series with the alternator field as the sketch I posted above shows.

Increasing the resistance lowers the amperage (I=V/R), lower amperage results in an initial weaker magnetic field being induced at the rotor.

Here is an electrical calculator http://www.rapidtables.com/calc/electri ... ulator.htm

Regards

Steve

[bob_rich]

oops!

typing got ahead of brain! when cold the resistance of a filament bulb is low. When hot it is much higher so really should have said the hot to cold resistance ratio can be as much as 8 -- not the way round I typed it above. Does not effect the reasoning for the point I was trying to make which was that bulbs can be very variable in resistance

apologies !

Bob

[billwill]

An extensive google search has indicated that the 'favourite' cause of this common problem; "Failure for the Alternator to start until revs are quite high" is that the charge indicator bulb is of too low a wattage. Other possibilities are dirty contacts on the wires of the warning bulb ccircuit or the earth.

Here is a description of how a person with a TVR fixed his version of the problem by adding another bulb in parallel.
http://www.pistonheads.com/gassing/topi ... 1&t=758799

Here is a rather early topic on our own forum here covering this issue.
elan-archive-f16/alternator-warning-lamps-etc-t10387.html

Here is a page that has a very pretty animated GIF image that shows what the circuits in the voltage regulator do to control the output of an alternator.
http://holdenpaedia.oldholden.com/Alter ... _Operation:


Summary:

A Regulator controls the current entering the Rotor. The greater the Rotor
Current, the more power the Alternator produces. It is the job of the Voltage Regulator to maintain the Alternator's Rated Output Voltage provided the RPM is high enough to produce the required load current and its maximum Current Output is not exceeded.

Alternator and Regulator Operation:
The Regulator turns the Field ON when the Indicator Voltage is less than 14 Volts
and turns the Field OFF when it is more than 14 Volts. It normally does this so fast that you cannot see it.

The average of the Regulator ON and OFF times produces the current required by the loads switched on at the time. In this way, the alternator output continually matches the load, and keeps the system voltage at the desired 14 Volts at the Output Terminal provided the Alternator is connected to a Battery.

Caution: If an Alternator is run without a Battery it can produce lethal voltages. While the average Voltage may still be 14 v, the peak Voltage can be as high as 100 volts.

[Plus 2]

For sure adding another bulb in parallel will have the effect of lowering the circuit resistance through the indicator lamps which are basically resistors in series to the alternator field (textbook electrics http://www.physicsclassroom.com/class/c ... l-Circuits ) The simple hand sketch I provided shows this without concerning oneself with the complete internal circuits of an alternator.

Indeed if paralleling two lamps solves such a problem then that would indicate simply an issue with the fitted lamp value or a problem with the present lamp or lamp holder which is creating a high resistance path due to a poor connection and that the inclusion of the second lamp is in effect creating in addition to lowering the overall resistance an easier path as the current will simply flow primarily through a line of least resistance.

Personally I would still opt for a thorough clean up of the present connections which includes the lamp and lamp holder as previously mentioned in one of the earlier posts before considering a twin lamp approach.

Alternatively placing a resistor in parallel across the lamp terminals will have the same effect and provide the additional piece of mind that if the indicator light does blow then the alternator will still receive a field current and the battery will always be charging when the car is restarted. This typical modification has been a standard practice for many car owners over the past 40 years I have been dealing with vehicle electrics. The theory the alternator will have held residual magnetism or self excite if engine revved to around 2000rpm I have found is NOT a given.

Bill I don't subscribe to being part of a forum designed to help fellow owners that just say's 'Google this and Google that' but the direct links you have supplied here are valuable information. Individuals surely should be able to ask a simple question and find members willing to assist first hand. The 200+ google links you provided me when I asked a question on Mick Miller driveshafts did NOT provide the answers to the question I asked BTW.

Regards

Steve

[billwill]

Bill I don't subscribe to being part of a forum designed to help fellow owners that just say's 'Google this and Google that' but the direct links you have supplied here are valuable information. Individuals surely should be able to ask a simple question and find members willing to assist first hand. The 200+ google links you provided me when I asked a question on Mick Miller driveshafts did NOT provide the answers to the question I asked BTW.

Regards

Steve

This afternoon I searched hundreds of Googled links to find those choice items above; it took about 3 hours. I'm really sorry if you found that kind of effort too much hassle in the case of the Mick Miller driveshafts, but on that occasion I was just on my way out to a meeting and if I don't know an answer, but I do know how an enquirer might find that answer, then I give the latter information.

Who knows, you might have been lucky and found what you were looking for with the first few links and got your answer long before I or any other member on here could give you a detailed answer.

The subject of how I choose to help enquirers is CLOSED, I've been here a long time and have helped many many people. How I do it is my concern.

[Plus 2]

Duplicated

[Plus 2]

Bill I don't subscribe to being part of a forum designed to help fellow owners that just say's 'Google this and Google that' but the direct links you have supplied here are valuable information. Individuals surely should be able to ask a simple question and find members willing to assist first hand. The 200+ google links you provided me when I asked a question on Mick Miller driveshafts did NOT provide the answers to the question I asked BTW.

Regards

Steve

This afternoon I searched hundreds of Googled links to find those choice items above; it took about 3 hours. I'm really sorry if you found that kind of effort too much hassle in the case of the Mick Miller driveshafts, but on that occasion I was just on my way out to a meeting and if I don't know an answer, but I do know how an enquirer might find that answer, then I give the latter information.

Who knows, you might have been lucky and found what you were looking for with the first few links and got your answer long before I or any other member on here could give you a detailed answer.

The subject of how I choose to help enquirers is CLOSED, I've been here a long time and have helped many many people. How I do it is my concern.

Bill,

I am certainly not criticsing your efforts but pointing out exactly what you confirm yourself.

Searching Google can be very time consuming.

I commend your efforts and anyone who puts this time in and the key is actually putting up the links and not just responding with 'google the issue' or 'search the library' IMHO.

For me I need to manage my time and stick to just answering the OP's concerns built up from what I have been trained or personal knowledge from actual hands on experience over 45 years owning and working on classic cars, coming from a family that founded one, if not the largest automotive OE component company in the UK, running my own automotive OE supply company and then working in a senior position for the UK's largest luxury car manufacturer under Ford ownership where I was responsible for producing the engineering prototype test cars.

I find in my later (early retired) years the time then spent responding can be quick and working on several forums which include Ferrari, Rolls Royce, MGB and several specialised electrical circuit design sites allows me more time to write a detailed personal response.

The variation on how people respond is what makes these forums valuable and why always best for any member to simply ask the question. Even if it has been asked before I still politely respond covering any OP's concerns.

Like I said in the PM's we traded had you used the 'quote' feature making it clear as you have now expressed in your PM response to me you were actually responding to 'troonsprint's' post who brought up the alternators I would not have even sought clarification on the fact your reply followed directly after my post and I felt it was belittling my efforts in assisting the OP.

I agree all sorted now and CLOSED.

I did pick up one interesting paragraph from the holdenpaedia site and I quote directly as copied and pasted

''A check showed the Charge light wasn't coming on which meant no excitation for the Rotor.

A while back on the forum the view became that the charge light
was not necessary for a Bosch 85 amp Alternator because they can self excite. I couldn't make mine self excite no matter how high the revs.

After driving the 20kms home at night, the 6 year old 530 CCA Delco Battery didn't have enough charge left in it to push over even one piston on an attempted start.''

This is simply one of my issues when searching websites in that it is easy to get contradictory information as Paul Hunt's comment on the MG website states the opposite and certainly exactly as I have posted previously self excitation must NOT be taken as a given.

Regards

Steve

[Robbie693]

Thanks guys, all this discussion is very illuminating if you'll forgive the pun.

I tried leaving the ignition on a while before cranking but the effect was the same. Next to try is investigating the bulb itself, maybe a while though as I'm on holiday at the moment.

For reference when I do get behind the dash, does anyone know what is the correct rating for the ignition warning light bulb?

Cheers

Robbie

[bob_rich]

Hi Robbie

The Lotus manuel gives warning lamps as style 281 (2W)

have a nice holiday best of luck

Bob

[Robbie693]

Great, cheers Bob

[gus]

When the alternator acts as the OP sees, it is thinking it is not getting sufficient regulator power.

TO test this, power the alternator from a temporary feed and see if the voltmeter confirms it. IOW, if the alternator outputs the correct voltage before blipping the throttle with a wire connected directly to the battery, the alternator is fine and the wiring via the light is suspect.

On the lucas alternator the light is attached to the regulator feed in such a way as the current draw powering the regulator lights the light. Once the alternator is charging it produces enough voltage to power itself and the light goes out.

Newer alternators have a wire with a transistor output that grounds the light when the alternator is not switched on

You will see the difference as with the lucas the lamp will fade in and out and the newer alternator it will simply switch on or off

[Robbie693]

Ok so I've been trying to change the bulb in the ignition warning light and as I pull the holder out I notice first, the green wire comes adrift, second it has a capless type bulb of 1.2W. Think this may be my problem.

Trouble is the BA7 bulb I bought will not fit the capless holder obviously so I need to get a new holder too. Could someone post up a pic of what the holder looks like please?

I found this : http://www.autoelectricsupplies.co.uk/product/456 but it only has one connection which I assume won't do. If anyone knows where I can get one that would be good too.

Cheers

Robbie

[Hawksfield]

Robbie

My 1971 +2s130 has cap less lamp holders for all the dash indication lamps, in addition they clip into the instrument cans, so you will be better sourcing the same type.

[Hawksfield]

Robbie

This is the type that is fitted to my car

http://www.ebay.co.uk/itm/T10-W5W-501-R ... 1135673382
Good Luck
John