Correct jacking points?
Discussion
jtong said:
Why? What does the alternator light *actually* indicate?
It indicates that the alternator output voltage is not the same as the ignition voltage. So: switch off with the engine revving and alternator output is 14 volts, ignition voltage is nil, light comes on. Similarly, switch ignition on with engine stationary, ignition voltage = 13 volts, alternator output = nil. Either way, the light comes on. One small point - the alternator needs a certain minimum revs before it will start charging. Hence it is normal for the light to stay on until the revs exceed about 1500 rpm (this figure does vary from car to car though).
Don't want to contradict an expert but I can remember DC generators, and as I remember it, the one big advantage an AC alternator always had over the generator was that it span faster and could charge the battery when the car was idling.
Ah, the days of sitting in traffic watching the ignition light flickering, revving it up from time to time -- only to give the tiny battery in my first Mini a charge, ossifer...
Ah, the days of sitting in traffic watching the ignition light flickering, revving it up from time to time -- only to give the tiny battery in my first Mini a charge, ossifer...
manek said: Don't want to contradict an expert but I can remember DC generators, and as I remember it, the one big advantage an AC alternator always had over the generator was that it span faster and could charge the battery when the car was idling.
Ah, the days of sitting in traffic watching the ignition light flickering, revving it up from time to time -- only to give the tiny battery in my first Mini a charge, ossifer...
It's true, an alternator charges more at any given speed than a dynamo and therefore can charge at idling speed. The only reason it does not charge until it has been revved up once is that the regulator has not cut in yet. Any alternator that does not start charging until over 2000 revs has got something wrong with it.
Ivan
shpub said: If you mean that it needs to be over 2000 revs constantly to charge then that is suspicious but the Ford alternators need to be taken to about 2500 revs to get them to start. Once triggered they behave.
No, that is incorrect, there is not an alternator Lucas or Bosch (Ford do not make alternators) that needs to be revved to 2500 revs to make the regulator cut in IF it is working properly and IF it is the right one for the car.
Ivan
No I'm confused.
The last time this happened the fault was a faulty 100A alternator fuse. My understanding is that this prevents the alternator from charging the battery.
When I first start the car, the alternator light stays on for a little while, and then goes out and stays out (normally after revving the engine). My car then properly broke down whilst driving along when the battery was eventually discharged enough to either confuse the ECU or not get a strong spark. At no point here did the alternator light come on. The alternator is not faulty AFAIK.
The last time this happened the fault was a faulty 100A alternator fuse. My understanding is that this prevents the alternator from charging the battery.
When I first start the car, the alternator light stays on for a little while, and then goes out and stays out (normally after revving the engine). My car then properly broke down whilst driving along when the battery was eventually discharged enough to either confuse the ECU or not get a strong spark. At no point here did the alternator light come on. The alternator is not faulty AFAIK.
Ivan
Have you ever owned a 2.9 TVR S?
>> Edited by shpub on Wednesday 30th April 12:11
Have you ever owned a 2.9 TVR S?
This is why many 2.9
litre V6 S owners start to panic when they start the
car and the ignition light does not go out at idle or
until about 2200 rpm is reached. This is normal and
due to the alternator/charging circuit, which requires
the alternator to produce a certain voltage and current
before it can charge. Until this is reached, power
is not supplied to the charging circuit and the ignition
light stays on. Once this rev limit has been exceeded,
charging continues even at lower revs e.g.
while just idling.
>> Edited by shpub on Wednesday 30th April 12:11
Hi, I'm a high-voltage electrical engineer really but I'll have a go at this....
I thought that the alternator light just indicated whether the alternator field winding was creating an output. The lamp is in the field winding circuit for the alternator. Alternators use 'self-excitation' which means that the alternator has to generate its own field current. It can't supply this excitation if it isn't generating, but if it's not 'excited', it can't generate - a vicious circle. So the battery provides the initial excitation and then once the alternator is spun up, as the engine starts, the alternator begins to supply its own excitation and the alternator light goes out.
If there is a break in the circuit between the alternator and the battery, the light may stay out as the alternator is still 'excited', i.e. attempting to generate. This is actually a bad situation for an alternator as you shouldn't open circuit the output terminals. I think this can cause the internal voltage of the alternator to increase to a damaging level?
Matt
Matt
I thought that the alternator light just indicated whether the alternator field winding was creating an output. The lamp is in the field winding circuit for the alternator. Alternators use 'self-excitation' which means that the alternator has to generate its own field current. It can't supply this excitation if it isn't generating, but if it's not 'excited', it can't generate - a vicious circle. So the battery provides the initial excitation and then once the alternator is spun up, as the engine starts, the alternator begins to supply its own excitation and the alternator light goes out.
If there is a break in the circuit between the alternator and the battery, the light may stay out as the alternator is still 'excited', i.e. attempting to generate. This is actually a bad situation for an alternator as you shouldn't open circuit the output terminals. I think this can cause the internal voltage of the alternator to increase to a damaging level?
Matt
Matt
shpub said: Ivan
Have you ever owned a 2.9 TVR S?
This is why many 2.9
litre V6 S owners start to panic when they start the
car and the ignition light does not go out at idle or
until about 2200 rpm is reached. This is normal and
due to the alternator/charging circuit, which requires
the alternator to produce a certain voltage and current
before it can charge. Until this is reached, power
is not supplied to the charging circuit and the ignition
light stays on. Once this rev limit has been exceeded,
charging continues even at lower revs e.g.
while just idling.
>> Edited by shpub on Wednesday 30th April 12:11
Steve,
No I have not owned a 2.9 TVR S.
If this happens on every 2.9 TVR S then what I would tell TVR or anyone else who sorted this installation is if they had done the job properly this situation would never have arisen. The reason this has happened is they needed to fit a smaller alternator pulley - very simple. This does not compromise the the life expectancy of the alternator in any way.
Ivan
taylormj4 said: Hi, I'm a high-voltage electrical engineer really but I'll have a go at this....
I thought that the alternator light just indicated whether the alternator field winding was creating an output. The lamp is in the field winding circuit for the alternator. Alternators use 'self-excitation' which means that the alternator has to generate its own field current. It can't supply this excitation if it isn't generating, but if it's not 'excited', it can't generate - a vicious circle. So the battery provides the initial excitation and then once the alternator is spun up, as the engine starts, the alternator begins to supply its own excitation and the alternator light goes out.
If there is a break in the circuit between the alternator and the battery, the light may stay out as the alternator is still 'excited', i.e. attempting to generate. This is actually a bad situation for an alternator as you shouldn't open circuit the output terminals. I think this can cause the internal voltage of the alternator to increase to a damaging level?
Matt
Matt
I am not too sure how this fits in with the theory side of things but here goes. There are basically two types of alternators, battery sensed and machine sensed. On a battery sensed unit it will only charge when there is already some voltage in the battery, it will not charge a completely flat battery (how daft is that)! On a machine sensed unit it starts to charge regardless once it spins up and is then controlled by the regulator. It needs the resistance of the warning light bulb to work, the dash side of the bulb is earthed.
Ivan
The 2.9 installation in the V8S is the same as the Ford as the engines were bought in complete. I have seen similar symptoms on Ford 2.9 cars so I suspect it is an inherited feature and nothing more sinister.
The 2.9 engine used alternators from Lucas, Bosch, Motorola, Mitsubishi and I have seen Marelli ones fitted as well. It may well be specific to a particular alternator as they have different regulator designs internally.
The explanation I have is that the alternator does indeed self excite but the regulator/controller switches over at a higher revs than expected and it is this regulator that causes this switch over funny. Not an issue as once triggered the alternator charges as normal.
When I first encountered it, I thought it was a fault as well but asking around, it is common on these cars with this engine. In all honesty, I suspect many do not notice it as the revs will be sufficient to trip and once excited the alternator behaves normally. It could also be due to variations in the trigger settings so that some switch at a lower voltage than others.
With a TVR, many people do not like over reving because of the engine wear and torque and so it is possible to drive the car carefully without reaching the revs trigger point and end up with a perceived fault. I had had my car some 6 months before I noticed it.
The 2.9 engine used alternators from Lucas, Bosch, Motorola, Mitsubishi and I have seen Marelli ones fitted as well. It may well be specific to a particular alternator as they have different regulator designs internally.
The explanation I have is that the alternator does indeed self excite but the regulator/controller switches over at a higher revs than expected and it is this regulator that causes this switch over funny. Not an issue as once triggered the alternator charges as normal.
When I first encountered it, I thought it was a fault as well but asking around, it is common on these cars with this engine. In all honesty, I suspect many do not notice it as the revs will be sufficient to trip and once excited the alternator behaves normally. It could also be due to variations in the trigger settings so that some switch at a lower voltage than others.
With a TVR, many people do not like over reving because of the engine wear and torque and so it is possible to drive the car carefully without reaching the revs trigger point and end up with a perceived fault. I had had my car some 6 months before I noticed it.
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