I don't see any mention of regulation, current or voltage in that quote. It appears to be a simplification....
Technical Alternator only starts generating after revving
- Thread starter nigelvan
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Technical Alternator only starts generating after revving
Thanks for all the replies. Yes, it occured to me 0.7V is exactly the forward voltage drop of a diode. It's actually closer to 0.75V
I keep seeing the 0.7V even with rpm over 700. I would also expect the BCM to stop sending current down that pin and start measuring, and lighting up E050 because it doesn't see 13+V on D+.
The wiring is at least partially functional because otherwise I wouldn't get back 14V on D+ once the alternator kicks in after revving up a bit.
If there was a high resistance situation further down the wiring I still would see the 1V expected when measing at the BCM or connector D004, instead of 0.7V.
A short after a diode in the alternator could explain why I only see 0.7V.
But... maybe the 0,7V is not related to a forward voltage drop of a diode and should be enough to excite the coils, in that case a high impededance further down the D+ line may be the cause. I had a similar issue with my high speed fan which signal/relay cable was partially broken...
In any case I'll have to disconnect D+ from the alternator and measure again, but I'm confused, should I measure 0.7V, 1V or battery voltage (12V) with an open circuit? It seems pin 25 of the BCM should only output 0.7V - 1V according to what I've read. I guess it's possible there's variation in the exact bias voltage required depending on which alternator is fitted in each vehicle...Or not?
I keep seeing the 0.7V even with rpm over 700. I would also expect the BCM to stop sending current down that pin and start measuring, and lighting up E050 because it doesn't see 13+V on D+.
The wiring is at least partially functional because otherwise I wouldn't get back 14V on D+ once the alternator kicks in after revving up a bit.
If there was a high resistance situation further down the wiring I still would see the 1V expected when measing at the BCM or connector D004, instead of 0.7V.
A short after a diode in the alternator could explain why I only see 0.7V.
But... maybe the 0,7V is not related to a forward voltage drop of a diode and should be enough to excite the coils, in that case a high impededance further down the D+ line may be the cause. I had a similar issue with my high speed fan which signal/relay cable was partially broken...
In any case I'll have to disconnect D+ from the alternator and measure again, but I'm confused, should I measure 0.7V, 1V or battery voltage (12V) with an open circuit? It seems pin 25 of the BCM should only output 0.7V - 1V according to what I've read. I guess it's possible there's variation in the exact bias voltage required depending on which alternator is fitted in each vehicle...Or not?
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With he D+ disconnected from the alternator I'd expect to see more than 1V coming from the BCM when masured with a DMM. Probably at least 4V. The fact that the D+ line come up to 14V when revved tends to indicate a BCM fault rather than a alternator fault.
So ye I agree, disconnect the D+, check output from BCM and then inject a small current into the alternator and see if it comes up. A small 12V incandescent indicator lamp is idea as a current source because it will act just like an old styple alternator light. Coming on with ignition and going out with engine running. If it does not go out until you rev the engine it is an alternator fault.
So ye I agree, disconnect the D+, check output from BCM and then inject a small current into the alternator and see if it comes up. A small 12V incandescent indicator lamp is idea as a current source because it will act just like an old styple alternator light. Coming on with ignition and going out with engine running. If it does not go out until you rev the engine it is an alternator fault.
Please just read here
www.fiatforum.com
Some of the last few replies are plain misleading
Post 30
Is correct
Back probe the body computer pin while cranking D+ should be battery voltage, sent from the body computer
if there's battery voltage here when cranking your looking for a break in the D+
if there's no voltage try disconnecting the D+ from the alternator, if it come back it likely to be a short in the alternator
With D+ still disconnected at the alternator measure the resistance between D+ and ground if it low there is a short in the wiring
if all that checked out you will need to have someone check the body computer, very unlikely as I have never seen one fail
No don't add volts to an unknown problem, if there is a short somewhere it could be an expensive repair
D+ should be 7-9V while disconnected at ignition on
There a problem D+ wire
Disconnect the coupling under the battery and measure the D+ from the body computer
If it's 7-9V there is a problem with the wiring down to
The alternator
If there is is no improvement the problem is upstream from this point
I have assumed
You do have a diesel
You don't have any leisure batteries
Or third party wiring
Battery warning light and no power steering | FIAT Bravo 2 (2007+)
In a way it's good news as I rather swap alternator than BCM. But it's still very puzzling.... Why wouldn't an non-OEM alternator work ? Every part shop being it online or indepentent garage offers Hella or Bosch for our cars. One should think there are numerous stories about the same problem...
www.fiatforum.com
Some of the last few replies are plain misleading
Post 30
Is correct
Back probe the body computer pin while cranking D+ should be battery voltage, sent from the body computer
if there's battery voltage here when cranking your looking for a break in the D+
if there's no voltage try disconnecting the D+ from the alternator, if it come back it likely to be a short in the alternator
With D+ still disconnected at the alternator measure the resistance between D+ and ground if it low there is a short in the wiring
if all that checked out you will need to have someone check the body computer, very unlikely as I have never seen one fail
No don't add volts to an unknown problem, if there is a short somewhere it could be an expensive repair
D+ should be 7-9V while disconnected at ignition on
There a problem D+ wire
Disconnect the coupling under the battery and measure the D+ from the body computer
If it's 7-9V there is a problem with the wiring down to
The alternator
If there is is no improvement the problem is upstream from this point
I have assumed
You do have a diesel
You don't have any leisure batteries
Or third party wiring
Diesel or Petrol is irrelevent.
OP has already measured the voltage as 0.7V when cranking and 14V when resisual magetism has kick-started the alternator. This strongly indicates a lack of excitation from the BCM. But an alternator or wiring fault is still possible.
An low current pull-up on the D+ line, either in place of the BCM or in paralell with it will prove or disprove the alternator (and wiring between alternator and point of current injection) functionality.
A pull up is also a cheaper fix than a BCM repair or replacement.
OP has already measured the voltage as 0.7V when cranking and 14V when resisual magetism has kick-started the alternator. This strongly indicates a lack of excitation from the BCM. But an alternator or wiring fault is still possible.
An low current pull-up on the D+ line, either in place of the BCM or in paralell with it will prove or disprove the alternator (and wiring between alternator and point of current injection) functionality.
A pull up is also a cheaper fix than a BCM repair or replacement.
Why is it every thing I say is an argument
It makes a difference
The petrol isn't computer controlled but a bulb on the dash
Would have to be typo in the first post a 3 instead of a 2 which is why I was checking
Or a short to ground
Or a break in the wire
Or a faulty component tapped into the D+
We don't know the integrity of the D+ cable
We don't know if some thing is tapped into the D+ line that's faulty
We haven't measured resistance of D+ disconnected to grounds
We don't know the voltage at the BSI
There's a very good chance if you excite the coil the alternator will work, but this does not help to understand the problem upstream
But bypassing a problem just to get something that works without investigating and understand the problem first isn't how I work,
And it isn't how I would advise someone on on open forum
Even fiat tap into the D+ for the optional heater
I have spent too long explaining everything instead of the thread moving forward, love the lesson on ohms law
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No sure where the problem is
According to fiat
"A voltage governor, also built into the alternator, maintains the power supply at a constant voltage (14 V) throughout all load variation and engine speed ranges.
Recharging system efficiency is controlled by the Body Computer node, which receives and measures the D+ signal from the alternator with the engine running (engine speed above 700 rpm)."
Or as the vast majority of 1 wire computer controlled alternator I have seen in the last 30 years
The internal regulator maintains the voltage at 14.1V ISH
The output is also controlled via computer altering the field current to insure there is enough as demand increases and reduce waste when its not needed
Yes lots of cars use a bulb, points, and carbs, but this isn't reliable,
Unless we have to rewire the car and retro fit a bulb, but we are a long way from that yet
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The exact wiring (lamp or BCM control) may depend on exact build date and market not just petrol or diesel.
Note I've never said "add volts" I said inject a small current.
If you read my posting I say that injecting current will prove the alternator AND wiring beteween injection point if the alternator then works. In that case the fault is the BCM or wiring between injection point and BCM.
This is called fault finding. Split the system in two and determine what half the fault is in.
The alternative is guess and swap parts which can get expensive.
I can't see why you have an objection to injecting a small current into a circuit node that normally swings between 0 and 14V with some current.
Robert.
Note I've never said "add volts" I said inject a small current.
If you read my posting I say that injecting current will prove the alternator AND wiring beteween injection point if the alternator then works. In that case the fault is the BCM or wiring between injection point and BCM.
This is called fault finding. Split the system in two and determine what half the fault is in.
The alternative is guess and swap parts which can get expensive.
I can't see why you have an objection to injecting a small current into a circuit node that normally swings between 0 and 14V with some current.
Robert.
Mine did the same but I put it off for for 2 years. 2011 2.3 130bph. 60,000 miles ,Motorhome . Ducato. Exact same symptoms.
Finally wouldn't charge at all. New alternator cured it. Right barstewed to change as once unbolted it won't come out of the engine bay. Had to unbolt engine mount and lift engine!
I tried all the other things first, just change the alternator.
Finally wouldn't charge at all. New alternator cured it. Right barstewed to change as once unbolted it won't come out of the engine bay. Had to unbolt engine mount and lift engine!
I tried all the other things first, just change the alternator.
New 140amp alternator in UK £130.00.
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I think that there may be something to be learnt by looking at the internals of the alternator, as shown on the two different diagrams.
The one shown for the petrol engine has the same internal configuration as shown on eLearn diagrams relating to my 2.8jtd. It depicts separate 3 phase half wave rectification for the regulator, which is depicted by a small square, and a narrower rectangle indicates the field or rotor. I understand this arrangement.
The icon for the alternator, in the drawing relating to the x250 diesel differs considerably. It has no separate half wave rectification for the regulator? which has a direct connection to one of the internal AC points. The D+ is shown as being connected to one of the brushes. Looking into the D+ connection you would probably see the diode drop of the negative diode pack via various windings.
What is the device to the left of the brushes, where I would expect a regulator to be? It seems to be labelled "RTE", but definition is not good. Also how does anything sense the alternator DC output? There does not appear to ba a direct connection.
The one shown for the petrol engine has the same internal configuration as shown on eLearn diagrams relating to my 2.8jtd. It depicts separate 3 phase half wave rectification for the regulator, which is depicted by a small square, and a narrower rectangle indicates the field or rotor. I understand this arrangement.
The icon for the alternator, in the drawing relating to the x250 diesel differs considerably. It has no separate half wave rectification for the regulator? which has a direct connection to one of the internal AC points. The D+ is shown as being connected to one of the brushes. Looking into the D+ connection you would probably see the diode drop of the negative diode pack via various windings.
What is the device to the left of the brushes, where I would expect a regulator to be? It seems to be labelled "RTE", but definition is not good. Also how does anything sense the alternator DC output? There does not appear to ba a direct connection.
No it's only the petrol what with the arguing
What's with the sarcasm
Exactly what I have already said
I haven't said swap the alternator
Continuity can be check with a multimeter which is far safer on an open forum, we don't know where the original poster is probing 100%
Because when the original poster said they wanted to add battery volts to an unknown circuit and I said stop
Two pages latter we are no further forwards
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You don't have to crawl under the van yet
At D004 there should be a yellow and red wire coming from a brown and geen
Uncouple D004
Brown and green should be 7-9V at ignition on
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Actually I was wondering if I could do that, I guess as long as I don't try to crank the engine (which won't work with D004 disconnected). I'll try this asap and report back.
dash light (I assume battery light E050): goes on with ignition as expected, goes out immediately when the engine is started (before revving), even without alternator generating (so it is out before revving up to start the alternator). Weird, because the ECU does raise the rpm to get the alternator started I supposed, but no battery light. RPM goes back to normal after revving and kickstarting the alternator.
Correct
I would also expect connected light on disconnect light off
I don't have a Ducato so can not confirm but that what happens with every other Fiat and the wiring is very similar
As expected, the BSI pumps out voltage and expects it dropped to below 4.5V via the internal resistance of the alternator D+ to ground should be around 1.5k
This should only happen if D+ is above around 5.5V, I guess at this point in time you have battery voltage but not 14.2V yet
Not sure here, some of the Ducato have alternators have both BSI and ECU control
It's a shame I don't have the resistance value for you particularly alternator, the original and replacement smaller fiats are 1.5K give or take, I know the upper limit on the 500 is 10k
While D004 is open you can check the resistance between D+ and ground without going under the car
Yellow and red cable to ground
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@koalar I did the measurements first thing this morning.
Pin 25 coming from M001 to D004 does indeed put out around 10V (open circuit). So I think we can say the BCM is doing its job.
Resistance from D004 to D+ (yellow/red wire) to ground is about 30-40 ohm. With 0.7V that's about 20-25mA going through the exciter circuit.
Wouldn't the resistance of the coils be much lower? Maybe it is a fault in the yellow/red wiring after all. If it's not that, we're looking for sure at the internals of the alternator, right?
Pin 25 coming from M001 to D004 does indeed put out around 10V (open circuit). So I think we can say the BCM is doing its job.
Resistance from D004 to D+ (yellow/red wire) to ground is about 30-40 ohm. With 0.7V that's about 20-25mA going through the exciter circuit.
Wouldn't the resistance of the coils be much lower? Maybe it is a fault in the yellow/red wiring after all. If it's not that, we're looking for sure at the internals of the alternator, right?
Co
But before we jump we need someone to measure a good Ducato alternator
Also slightly annoyingly you will have to disconnect the the D+ and check it's 30 ohms D+ to case and not the yellow and red wire
I would not be confident in calling it until someone else has measured theirs first
I would not be confident of injecting battery voltage
It is normal If the ECU detects the wrong current it cuts the output to the exiter, for example before doing the field winding test with Fiats examiner you have to clear the codes on ECU first
Which reminds me you have checked and cleared all ECU codes ?
Replacement isn't the only option
I had a small alternator fixed by a company here in the UK while I waited, came with warranty, I wasn't paying so can't remember the price, pretty cheap if you took the alternator off yourself, they also did a drive in fit and replace service while you waited, not sure if the same sort of service is available in
Belgium
Correct, plus we know the continuity of this cable is good., we can leave it there
30-40 ohms does not sound right to me, the Punto, Panda, Bravo have all been around 1.5K ohms,
What we need is the measurements from Ducato owner, D+ to alternator case, but unfortunately it looks to me like one of the diodes inside the alternator has gone short, the coils themselves are normally around 30 ohms,
But before we jump we need someone to measure a good Ducato alternator
Also slightly annoyingly you will have to disconnect the the D+ and check it's 30 ohms D+ to case and not the yellow and red wire
I would not be confident in calling it until someone else has measured theirs first
I would not be confident of injecting battery voltage
It is normal If the ECU detects the wrong current it cuts the output to the exiter, for example before doing the field winding test with Fiats examiner you have to clear the codes on ECU first
Which reminds me you have checked and cleared all ECU codes ?
Replacement isn't the only option
I had a small alternator fixed by a company here in the UK while I waited, came with warranty, I wasn't paying so can't remember the price, pretty cheap if you took the alternator off yourself, they also did a drive in fit and replace service while you waited, not sure if the same sort of service is available in
Belgium
I live in Belgium so I'll have to find my own company ;-).
But yes, next I'll check the wire between D004 and D+ including the connector.
But if the resistance is indeed way too low I'll be looking at the alternator itself. Btw it doesn't need much revs to get it started. It could be possible the coil is at least partially energized but that's just guessing.
If the coils themselves are 30 ohms but normally you would measure 1.5K ohm, what else is in the circuit? A diode itself doesn't have any (or very little) resistance when in forward bias, right?
If I knew more about the internals of the voltage regulator (I know how it recitfies the AC into DC, that's pretty straight forward). Maybe I can pull out the regulator alone but I know there's not much space to work on at the back of the 3L diesel. Been there before to replace the belt. I did visually check the D+ connector to the alternator back then but not really thourough.
I agree with you injector battery voltage into D+ to test it is not the way to go. Even if it does start it still doesn't offer a solution, now that we know BCM is doing alright.
But yes, next I'll check the wire between D004 and D+ including the connector.
But if the resistance is indeed way too low I'll be looking at the alternator itself. Btw it doesn't need much revs to get it started. It could be possible the coil is at least partially energized but that's just guessing.
If the coils themselves are 30 ohms but normally you would measure 1.5K ohm, what else is in the circuit? A diode itself doesn't have any (or very little) resistance when in forward bias, right?
If I knew more about the internals of the voltage regulator (I know how it recitfies the AC into DC, that's pretty straight forward). Maybe I can pull out the regulator alone but I know there's not much space to work on at the back of the 3L diesel. Been there before to replace the belt. I did visually check the D+ connector to the alternator back then but not really thourough.
I agree with you injector battery voltage into D+ to test it is not the way to go. Even if it does start it still doesn't offer a solution, now that we know BCM is doing alright.
