Technical Alternator only starts generating after revving

[bugsymike]

Found this:-
The voltage is totally controlled and set by the CPU. Advanced protocols use a PWM (pulse width modulation) type encoding. The pulse width of the signal sent by the CPU to the alternator determines the voltage regulation. Essentially, it’s still a one-way communication flow.
The alternator and internal voltage regulator are connected to battery positive through a 100-amp fuse located in the underhood fuse box. The ECM controls charging voltage via a square-wave signal sent through a Local Interconnect Network (LIN) communications wire to the voltage regulator.

 

[koalar]

Things change but this isn't a modern transit or high end Honda

As far as I know the van does not have a smart electric load detection alternator it's just a dumb system, and once the battery is fully charged the excess is just wasted

Load lamp, ELD alternator , pulley clutch and so on just don't apply



D+

1V ish at ignition on(officially under 5.5V)
If above 5.5V the lamp will stay lite. High current items mybe switched off. Glow plugs, EPS

Battery voltage while cranking

Above 750 Rpm D+ should equal B+

Warning light comes on if B+ falls below 5.5V while engine running.

Let's keep it simple

If the above check out okay and the belt isn't slipping, I'd be looking at the alternator itself next.

 

[nigelvan]

Ok guys, This might be a stupid question, but once I identified the correct connector and pin, how am I supposed to measure the voltage without removing the connector? Btw I've found my old thread where I was looking for D+ when I was installing my battery charger:

 

[nigelvan]

Things change but this isn't a modern transit or high end Honda

As far as I know the van does not have a smart electric load detection alternator it's just a dumb system, and once the battery is fully charged the excess is just wasted

Load lamp, ELD alternator , pulley clutch and so on just don't apply



D+

1V ish at ignition on(officially under 5.5V)
If above 5.5V the lamp will stay lite. High current items mybe switched off. Glow plugs, EPS

Battery voltage while cranking

Above 750 Rpm D+ should equal B+

Warning light comes on if B+ falls below 5.5V while engine running.

Let's keep it simple

If the above check out okay and the belt isn't slipping, I'd be looking at the alternator itself next.

Correct, but the excess isn't wasted: the voltage regulator will determine the exciter voltage which will increase or decrease the magnetic field, making the rotor harder or easier to turn and thus generating the exact amount of current to maintain 14V. This is because the rpm of the engine also varies while driving, together with the demand for power by various electrical systems.

 

[koalar]

Correct, but the excess isn't wasted: the voltage regulator will determine the exciter voltage which will increase or decrease the magnetic field, making the rotor harder or easier to turn and thus generating the exact amount of current to maintain 14V. This is because the rpm of the engine also varies while driving, together with the demand for power by various electrical systems.

I did over simplify it

But It's a dumb system which is why modern car you see the voltage constantly changing between 12-15V

Here it maintains 14.1V regardles

The exsess is wasted as heat and bubbles if the battery no longer needs it

 

[koalar]

Ok guys, This might be a stupid question, but once I identified the correct connector and pin, how am I supposed to measure the voltage without removing the connector? Btw I've found my old thread where I was looking for D+ when I was installing my battery charger:

View attachment 421895

Bottom left looks likely red clip locking the two halfs of the coupling

Get a decent close up of one side where I can see the colours or jot them down and I will see if I can match them

Going out for a few hours

I back probe with a T pin


As here on a panda, ignition on

 

[nigelvan]

It might be the blue one since I see a green/yellow wire there.
Do I risk anything by unplugging these connectors (I don't think so but I never messed with the electronics beside some OBD stuff and installing a new radio). Since these connectors are shaped in a 90 degree angle it might be hard to reach them, even with a needle. I might postpone this until we are back home on the driveway at the end of May.

 

[nigelvan]

Update: We're still in France so no chance yet to look at it closer. But the problem went away... I did have a problem with my DC-DC charger when an automotive fuse came loose and melted the socket it was in. While this seems coincidental I think it's also unrelated as this charger only powers on when it sees a voltage >13.3V.
The van was parked on the driveway for 1.5 months when this problem arose, so maybe some humidity is involved? To be continued...

 

[nigelvan]

Things change but this isn't a modern transit or high end Honda

As far as I know the van does not have a smart electric load detection alternator it's just a dumb system, and once the battery is fully charged the excess is just wasted

Load lamp, ELD alternator , pulley clutch and so on just don't apply



D+

1V ish at ignition on(officially under 5.5V)
If above 5.5V the lamp will stay lite. High current items mybe switched off. Glow plugs, EPS

Battery voltage while cranking

Above 750 Rpm D+ should equal B+

Warning light comes on if B+ falls below 5.5V while engine running.

Let's keep it simple

If the above check out okay and the belt isn't slipping, I'd be looking at the alternator itself next.

So, I know a year went by and nothing really changed. The problem came back and we just went along with it.
Because a few other repairs (high speed fan cable broke) I got a bit more familiar with the electricals and measured D+ now at various points.
D+ is 0.7V at M001 (BCM), D004 (connector under fuse box) while ignition on and before alternator had a rev to start up, after that, 14V.
I was planning to put 12V on it to see if it would excite the coils but after reading it should be 1V I refrained from doing that, fearing to cause a voltage spike. Couldn't get to the actual alternator yet, that's for next week probably when I'll replace the right front brake pistons dust boots.
Cleaned all positive high current contacts (at junction box, at the starter motor) with dremel and contact cleaner. Checked again for a bad earth situation but no voltage drop between chassis and block.
E050 battery light stays off
Voltage is stable when revving the engine (14.2 - 14.5V)

Only thing I can think of now is the connector to the alternator or the voltage regulator circuit. Communicator suggested bad brushes in a new thread I created for this issue (I forgot about this one, sorry)

 

[koalar]

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

 

[nigelvan]

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

Thanks for the reply after all this time! I checked both at D004 (easy access) and M001 (pin 25, reachable with a needle when sliding out the 2 subconnectors from the main 'blue' connector). Voltage stays 0.7V at ignition and while cranking the same. It only jumps to 14V after revving and the alternator kicks in...
I have an electronics background and I agree it is very unlikely the BCM at fault, as I would probably see other things fail as well, but it is possible, after all...But more likely a short in the alternator then.
Will disconnect the alternator next and do the same test again.

I thought the alternator connector would be up next to check, but if you say D+ should be 12V while cranking, a bad connection there is very unlikely.

 

[koalar]

Wiri

Thanks for the reply after all this time! I checked both at D004 (easy access) and M001 (pin 25, reachable with a needle when sliding out the 2 subconnectors from the main 'blue' connector). Voltage stays 0.7V at ignition and while cranking the same. It only jumps to 14V after revving and the alternator kicks in...
I have an electronics background and I agree it is very unlikely the BCM at fault, as I would probably see other things fail as well, but it is possible, after all...But more likely a short in the alternator then.
Will disconnect the alternator next and do the same test again.

I thought the alternator connector would be up next to check, but if you say D+ should be 12V while cranking, a bad connection there is very unlikely.

Wiring in more likely

Such as here

fiat ducato 2007 not charging | FIAT Ducato

i guess the L-DFM cable is this. If yes, seems very easy to be cut off.

www.fiatforum.com

 

[g8rpi]

Connecting the D+ line to a current limited source of up to battery voltage should not damage anything as it is within the normal operating range for that line. Try a small incandescent indicator lamp between an ignition switched +12V supply and the D+ line. A 470 ohm 1/2 watt resistor would also do.
It looks to me like the BCM is not providing enough bias voltage to excite the alternator. It works when you rev it due to residual magnetism in the rotor.
If you are really worried about damaging the BCM break the connecton and only connect the lamp to the alternator. That will at least prove the circuit from there to the alternator. The lamp could be a permanent fix as an alternative to a new or repaired BCM.

 

[koalar]

Adding the battery voltage as it is does not add anything to the party or fetch use any further forwards to properly repair the problem

Besides which add 5 Amps to activate the exciter coils in an unknown circuit is in my opinions is unsafe

Limiting the current in this situation will not work as it needs the current to excite the coils

 

[g8rpi]

Hi Koalar,
I have to disagree.
It will tell us if the alternator starts up with external excitiation. It would lso confirm, if alternator starts, the connection pathe from the injction point.
Not sure where you get 5 amps from. I'm thinking 25 to 100mA from a resistor or indicator lamp. This is more than enough to get the alternator started. Millions of cars used an indicator lamp for inital excitation for many decades.

The difference between the 1.01 V excitaition you measured and the 0.7V Nigel is reporting is small but significant. 0.7V is the forward voltage drop of a silicon diode. This could mean a fault in the alternator (low impedance on the other side of a diode) or the BCM / wiring impedance is not passing enough current to drop any voltage across the field winding. In this case the only drop is across the rectifier which will show 0.7V regardless of current. If your (Koala) BCM is driving 100mA then there may be 0.3V across the field coil. This indicates a 3 Ohm field coil (Ohms law) which is entirely reasonable.

Robert.

 

[Communicator]

Hi Koalar,
I have to disagree.
It will tell us if the alternator starts up with external excitiation. It would lso confirm, if alternator starts, the connection pathe from the injction point.
Not sure where you get 5 amps from. I'm thinking 25 to 100mA from a resistor or indicator lamp. This is more than enough to get the alternator started. Millions of cars used an indicator lamp for inital excitation for many decades.

The difference between the 1.01 V excitaition you measured and the 0.7V Nigel is reporting is small but significant. 0.7V is the forward voltage drop of a silicon diode. This could mean a fault in the alternator (low impedance on the other side of a diode) or the BCM / wiring impedance is not passing enough current to drop any voltage across the field winding. In this case the only drop is across the rectifier which will show 0.7V regardless of current. If your (Koala) BCM is driving 100mA then there may be 0.3V across the field coil. This indicates a 3 Ohm field coil (Ohms law) which is entirely reasonable.

Robert.

I agree that the proposed injection of a small current into the the alternator field winding, while disconnected from the BCM, should prove the alternator and wiring as suggested.

I can also agree with the deduction of alternator field resistance. Years ago I installed a pulsed charging system for the 70A alternator on my 1990 manufactured Talbot Express. I have a measurement of rotor resistance of 3.7 Ohms, which suggests an excitation current of about 3A.

 

[koalar]

Please let me carefully here

We don't know if the original poster is on the correct wire

The original poster was not going to limit the current

We don't know if the wiring is damaged

We don't know if the computer is damaged

This is a computer controlled alternator

From ignition on the computer pumps out around 9V

This is pulled down via the internal wiring to around 1V

During cranking the computer ups the currents my little panda is 3 amps

Once the engine revs past 750 rpm the current is cut,

The computer then monitors this cable and adjusts the current as nessasary to demand


If you want to test the alternator is working, disconnect the B+ terminal first

Anything else I would use a test light (200mA) or multimeter

But each to there own

 

[g8rpi]

You need to make your mind up. Earlier you said it was a "dumb" system.
I'm basing it on a dumb system. The BCM does not control the alternator in any way. It just simulates the old alternator light system. This is injecting a small current into the field teminal when the alternator not turning. As the the alternator come online the voltage on the field terminal rises to ~14V in the old sytem this meant no voltage across the indicator lamp (lamp out) the BCM just monitors the voltage to determine the alternator is working.
The field teminal does not control the alternator output. It is just an independent supply for the field. It is derived from a dedicated rectifier in the alternator. The indicator light / BCM just supplies a low voltage current to get things started.
I've had formal training in this stuff and am qualified to test, repair and certify such ystems on aircraft. Small aircraft use identical systems.
The OP has an electronic background so I'm sure he can understand limiting the current.

Robert.

 

[g8rpi]

Even on smart alternators the BCM does not control current, certainly not in the alternator field. It just "tells" the alternators internal regulator what output voltage to produce based on calculated load and battery state of charge. This is purely for fuel saving.

 

[koalar]

Even on smart alternators the BCM does not control current, certainly not in the alternator field. It just "tells" the alternators internal regulator what output voltage to produce based on calculated load and battery state of charge. This is purely for fuel saving.

Not according to fiat elearn

and has done since about the 90s

There's only two wires

One is the output

The exactor also controls the field strength