OT car alternator excitor...

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Sorry for the offtopic post, but I think the people here might know the answer.

How does an automobile alternator exciter work? Is it a coil in the alternator that somehow keeps the main coil from working or is it a relay or semiconductor type switch that prevents the alternator from acting like a motor when the car is not running?

Thanks
 
On Wed, 19 Oct 2022 03:10:44, Wanderer@noplace.com wrote:

Sorry for the offtopic post, but I think the people here might know the answer.

How does an automobile alternator exciter work? Is it a coil in the alternator that somehow keeps the main coil from working or is it a relay or semiconductor type switch that prevents the alternator from acting like a motor when the car is not running?

Thanks
Click to expand...

Most car alternators have a rotating field, an electromagnet that
spins and pushes flux into the output stator windings. The field coil
needs 0 to 12 volts, depending on how much output current one needs.

A voltage regulator or engine control computer adjusts the field
current as needed.

The AC output of the stator windings is rectified by a bunch of
diodes. Such a rig can\'t be back-driven to act as a motor. Maybe some
hybrids use one gadget as both generator and motor.

Small engines and some cars have rotating permanent-magnet fields.
Their output is regulated by shorting.

I did a lot of research on PM alternators.

https://www.dropbox.com/s/ufadube8ttkksdv/DSC04228.JPG?raw=1

https://www.dropbox.com/s/zv0y36che7gmglr/Deere_3.JPG?raw=1

https://www.dropbox.com/s/hwarwzy0cduneam/Deere_2.JPG?raw=1
 
The excitor got stuck on when the car was off and the alternator would pull 4 amps and kill the battery. The battery light didn\'t go on. Now the excitor is stuck off, the battery light stays on and the alternator doesn\'t pull any current. I\'m wondering if I need to replace the whole alternator or just the regulator. I\'m having trouble wrapping my brain about what is going on. I\'m thinking the excitor signal somehow connects the alternator output to the exciter coil input and that the exciter signal wire doesn\'t really power any coils. But I\'m not sure. If the coil is gone, then I need a whole new alternator. But it might be just some semiconductor that can be replaced. I wish they had schematics for these things.
 
onsdag den 19. oktober 2022 kl. 23.14.52 UTC+2 skrev Wand...@noplace.com:
The excitor got stuck on when the car was off and the alternator would pull 4 amps and kill the battery. The battery light didn\'t go on. Now the excitor is stuck off, the battery light stays on and the alternator doesn\'t pull any current. I\'m wondering if I need to replace the whole alternator or just the regulator. I\'m having trouble wrapping my brain about what is going on. I\'m thinking the excitor signal somehow connects the alternator output to the exciter coil input and that the exciter signal wire doesn\'t really power any coils. But I\'m not sure. If the coil is gone, then I need a whole new alternator. But it might be just some semiconductor that can be replaced. I wish they had schematics for these things.
Click to expand...

a car from this century?
 
On Wednesday, October 19, 2022 at 5:14:52 PM UTC-4, Wand...@noplace.com wrote:
> The excitor got stuck on when the car was off and the alternator would pull 4 amps and kill the battery. The battery light didn\'t go on. Now the excitor is stuck off, the battery light stays on and the alternator doesn\'t pull any current. I\'m wondering if I need to replace the whole alternator or just the regulator. I\'m having trouble wrapping my brain about what is going on. I\'m thinking the excitor signal somehow connects the alternator output to the exciter coil input and that the exciter signal wire doesn\'t really power any coils. But I\'m not sure. If the coil is gone, then I need a whole new alternator. But it might be just some semiconductor that can be replaced. I wish they had schematics for these things.

there\'s something wrong with your ignition circuit. It\'s not removing power from the regulator when turned off. There could be some other failure and sneak circuit putting voltage to the regulator. It\'s up to you to debug it. Sounds like that extended 4A through the excitor damaged it, and it may need to be replaced. But don\'t do that until you find out why that regulator/excitor remains powered up when the ignition is turned to ff.
 
On Wed, 19 Oct 2022 05:14:35, Wanderer@noplace.com wrote:

>The excitor got stuck on when the car was off and the alternator would pull 4 amps and kill the battery. The battery light didn\'t go on. Now the excitor is stuck off, the battery light stays on and the alternator doesn\'t pull any current. I\'m wondering if I need to replace the whole alternator or just the regulator. I\'m having trouble wrapping my brain about what is going on. I\'m thinking the excitor signal somehow connects the alternator output to the exciter coil input and that the exciter signal wire doesn\'t really power any coils. But I\'m not sure. If the coil is gone, then I need a whole new alternator. But it might be just some semiconductor that can be replaced. I wish they had schematics for these things.

The alternator could have shorted diodes. But more likely the
regulator is trashed. Disconnect the field wire and see if the current
drain goes away. 4 amps might be about what the field uses.

What do you mean by \"excitor coil?\"
 
John Larkin <jlarkin@highland_atwork_technology.com> wrote:
The alternator could have shorted diodes. But more likely the
regulator is trashed. Disconnect the field wire and see if the current
drain goes away. 4 amps might be about what the field uses.
Click to expand...
It might be useful to search for \"diode trio\" online. IIRC Delco
alternators used two sets of rectifiers: The main full-wave set,
for the charging output, and a second half-wave \"trio\" that provides
DC power to run the voltage regulator. This allows a switched DC
input to drive the field which is isolated from the battery and
relatively isolated from output loading once up to speed.

What do you mean by \"excitor coil?\"
Click to expand...

Perhaps a reference to a separate stator winding, additional to the
\"diode trio\" that provides excitation power that\'s more isolated
from the influence of load on the main output. Not used in auto
alternators AFAIK, but common in AC mains type alternators.

I do have a Delco schematic from an old manual. If there\'s
interest I could scan and post it.

hth,

bob prohaska
 
bob prohaska <bp@www.zefox.net> wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

The alternator could have shorted diodes. But more likely the
regulator is trashed. Disconnect the field wire and see if the current
drain goes away. 4 amps might be about what the field uses.

It might be useful to search for \"diode trio\" online. IIRC Delco
alternators used two sets of rectifiers: The main full-wave set,
for the charging output, and a second half-wave \"trio\" that provides
DC power to run the voltage regulator. This allows a switched DC
input to drive the field which is isolated from the battery and
relatively isolated from output loading once up to speed.

What do you mean by \"excitor coil?\"


Perhaps a reference to a separate stator winding, additional to the
\"diode trio\" that provides excitation power that\'s more isolated
from the influence of load on the main output. Not used in auto
alternators AFAIK, but common in AC mains type alternators.

I do have a Delco schematic from an old manual. If there\'s
interest I could scan and post it.

hth,

bob prohaska
Click to expand...

No need. Google has a wealth of information on alternators.

Search: alternator schematic

Here is one result that discusses different types of alternators and
regulators:

Alternator Voltage Regulation 101 (with Wiring Diagrams)

https://www.carparts.com/blog/alternator-voltage-regulation-101-with-
wiring-diagrams/




--
MRM
 
Here\'s wikipedia

https://en.wikipedia.org/wiki/Excitation_(magnetic)#Separate_excitation

This is why I call it an exciter coil, though I keep spelling exciter wrong.

https://upload.wikimedia.org/wikipedia/en/b/b0/Separately_Excited.png

I guess you refer to it as a field coil. I think the alternator in the car looks something like this.

https://upload.wikimedia.org/wikipedia/commons/8/83/Serie_Shunt_Coumpound.png

with the addition of a rectifier/regulator between the M and the plus and minus outputs.

I think in old cars the \'f\' field coil went directly to the battery light and the ignition, but when I unplugged the exciter wire, the exciter stayed stuck on. Now that short has burned out and the exciter is stuck off but the battery light is on so something is there grounding the light bulb.

So my question is: Does the exciter wire directly power the field coil or does the exciter wire go to a transistor or something that turns the field coil on? Is there a transistor or diode I can replace?

Yes there are schematics on the internet but I have not found any that go beyond black boxes for the regulator and the alternator. Basically they\'re just wiring diagrams for the car and not circuit diagrams.

It\'s an old car, A 1997 VW GTI VR6. If it was a new car I would buy a new alternator. But in an old car, you have to consider how much money to put in to it before the next thing breaks and when do you give up?
 
On 2022-10-19, Wanderer@noplace.com <Wanderer@noplace.com> wrote:
Sorry for the offtopic post, but I think the people here might know the answer.

How does an automobile alternator exciter work? Is it a coil in the alternator that somehow keeps the main coil from working or is it a relay or semiconductor type switch that prevents the alternator from acting like a motor when the car is not running?

Thanks
Click to expand...

the typical circuit powers the regulator through the alternator
warning lamp, and through an auxillary positive tap on the main
rectifier, if you\'re seeing 4A flowing into the regulator it\'s
busted. (and probably the lamp too)

If you had 4A flowing through the field winding with the motor stopped
the alternator is cooked, (also busted)

--
Jasen.
 
the typical circuit powers the regulator through the alternator
warning lamp, and through an auxillary positive tap on the main
rectifier, if you\'re seeing 4A flowing into the regulator it\'s
busted. (and probably the lamp too)

If you had 4A flowing through the field winding with the motor stopped
the alternator is cooked, (also busted)
Click to expand...

You\'re probably right, but ...

The exciter got stuck on and pulled 4 amps with the car off. With the car on, the alternator worked normally. Produced around 14.5V regardless of the RPMs on the engine, so the regulator was working. I disconnected the exciter wire and the exciter stayed on and the car still worked. I\'m a clever engineer so I put a big hundred amp shottkey diode between the starter motor and the alternator to stop the reverse current flow. But that turned the exciter off and the exciter wire wouldn\'t turn it on. Removing the diode turning the exciter back on and the car worked again. I would have to disconnect the battery when the car was off but when it was running the car was fine. Then one day I connected the battery, tried to start the car and the battery lamp came on. The exciter was off, the alternator no longer worked but the exciter does connect to ground to cause the lamp to go on and the lamp works. So I think the field coil is not directly powered by the exciter wire. I can imagine a circuit with a transistor. The exciter wire connects to the base, the emitter connects to the field coil and the collector to the output of the regulator.

The real problem is that this alternator is buried deep in the engine and I have to dismantle half the car to get there. I don\'t have a garage and winter is coming. I\'m a slow mechanic. Things usually go sideways for me and I need to wait a week for a part or tool to fix some unexpected problem. So I\'m going to wait until next summer. I think the car is sidelined by a burnt out $5 transistor deep inside the engine, but you might be right and I need a whole new alternator.

I\'m just frustrated and posting stupid questions on usenet.
 
On 2022-10-25 12:56 p.m., Wanderer@noplace.com wrote:
the typical circuit powers the regulator through the alternator
warning lamp, and through an auxillary positive tap on the main
rectifier, if you\'re seeing 4A flowing into the regulator it\'s
busted. (and probably the lamp too)

If you had 4A flowing through the field winding with the motor stopped
the alternator is cooked, (also busted)

You\'re probably right, but ...

The exciter got stuck on and pulled 4 amps with the car off. With the car on, the alternator worked normally. Produced around 14.5V regardless of the RPMs on the engine, so the regulator was working. I disconnected the exciter wire and the exciter stayed on and the car still worked. I\'m a clever engineer so I put a big hundred amp shottkey diode between the starter motor and the alternator to stop the reverse current flow. But that turned the exciter off and the exciter wire wouldn\'t turn it on. Removing the diode turning the exciter back on and the car worked again. I would have to disconnect the battery when the car was off but when it was running the car was fine. Then one day I connected the battery, tried to start the car and the battery lamp came on. The exciter was off, the alternator no longer worked but the exciter does connect to ground to cause the lamp to go on and the lamp works. So I think the field coil is not directly powered by the exciter wire. I can imagine a circuit with a transistor. The exciter wire connects to the base, the emitter connects to the field coil and the collector to the output of the regulator.

The real problem is that this alternator is buried deep in the engine and I have to dismantle half the car to get there. I don\'t have a garage and winter is coming. I\'m a slow mechanic. Things usually go sideways for me and I need to wait a week for a part or tool to fix some unexpected problem. So I\'m going to wait until next summer. I think the car is sidelined by a burnt out $5 transistor deep inside the engine, but you might be right and I need a whole new alternator.

I\'m just frustrated and posting stupid questions on usenet.
Click to expand...

The Alternator uses a 6 diode 3 phase bridge to rectify the 3 phase
voltage produced to charge the battery. This blocks any reverse current
such as trying to power the alternator as a motor.

The alternator acts as a current source but with sufficient voltage at
an idle RPM to charge the battery. This is controlled by a variable
current to ground to the exciter winding which as V+ on the other end
internally. Think of this like a current controlled magnetic coupler
from stator to rotor to couple more output current if the engine is
running and the demand current is sensed by a battery voltage less than
the internal regulator reference of 14.2V (typ.)

The alternator has this magnetic current gain then from exciter field
winding current to battery output current, that might be from 4A in to
120 A out depending on the rating of the alternator.

That\'s how it works.

 
The Alternator uses a 6 diode 3 phase bridge to rectify the 3 phase
voltage produced to charge the battery. This blocks any reverse current
such as trying to power the alternator as a motor.

The alternator acts as a current source but with sufficient voltage at
an idle RPM to charge the battery. This is controlled by a variable
current to ground to the exciter winding which as V+ on the other end
internally. Think of this like a current controlled magnetic coupler
from stator to rotor to couple more output current if the engine is
running and the demand current is sensed by a battery voltage less than
the internal regulator reference of 14.2V (typ.)

The alternator has this magnetic current gain then from exciter field
winding current to battery output current, that might be from 4A in to
120 A out depending on the rating of the alternator.

That\'s how it works.
Click to expand...

Interesting. What does the exciter wire do?
 
On 2022-10-31, Wanderer@noplace.com <Wanderer@noplace.com> wrote:
The Alternator uses a 6 diode 3 phase bridge to rectify the 3 phase
voltage produced to charge the battery. This blocks any reverse current
such as trying to power the alternator as a motor.

The alternator acts as a current source but with sufficient voltage at
an idle RPM to charge the battery. This is controlled by a variable
current to ground to the exciter winding which as V+ on the other end
internally. Think of this like a current controlled magnetic coupler
from stator to rotor to couple more output current if the engine is
running and the demand current is sensed by a battery voltage less than
the internal regulator reference of 14.2V (typ.)

The alternator has this magnetic current gain then from exciter field
winding current to battery output current, that might be from 4A in to
120 A out depending on the rating of the alternator.

That\'s how it works.

Interesting. What does the exciter wire do?
Click to expand...

It powers an elecromagnet in the rotor of the altenator.
that makes the rotating magnetic field that generates
the EMF that produces the electric current.

--
Jasen.
 
Jasen Betts <usenet@revmaps.no-ip.org> wrote:

Interesting. What does the exciter wire do?

It powers an elecromagnet in the rotor of the altenator.
that makes the rotating magnetic field that generates
the EMF that produces the electric current.

Jasen.
Click to expand...

Suggest you look at https://en.wikipedia.org/wiki/Alternator_(automotive) for
more information. Also see

1. https://www.youtube.com/watch?v=jdSKlg80DjU
2. https://www.youtube.com/watch?v=QXlOSRjJT8g
3. https://www.youtube.com/watch?v=ab5Kk6JkbsI

- and many other links.


--
MRM
 
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