wammers said:
Don't worry nobody upset. How does the controller know when the battery is depleted and when it is full unless the battery voltage is being monitored? As the battery voltage falls by being drawn on the field voltage is turned up, as it gets full the field voltage is turned down. How does the controller know to do that? Does it have ESP?
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They're all connected to the same bit of wire the voltage drop will be across the board which the regulator on the alternator will try to deal with. No external control is required - or indeed possible within margins of sanity and expense. :)
 
Fairly easily, I would suggest.
Using V=IR, the resistance of the battery changes according to its charge state.
 
StuckAgainSteve said:
They're all connected to the same bit of wire the voltage drop will be across the board which the regulator on the alternator will try to deal with. No external control is required - or indeed possible within margins of sanity and expense. :)
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So the voltage drop is monitored? Nobody mentioned external control.
 
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wammers said:
So the voltage drop is monitored? Nobody mentioned external control.
Click to expand...

No, not monitored, as electrical load tries to pull voltage down, the (internal) regulator will increase output current until the voltage matches the fixed value the regulator is designed to output - it's as simple as that.
 
PS you may have been confused by the latest alternators which are controlled electronically, the exciter current is switched off during full throttle (assuming battery voltage is good) or bumped up to full amperage when the throttle is closed and the engine above target idle value (ie engine braking) there are new bosch systems which combine the function of an alternator and starter motor working in two modes 12 volt and 36 (if I remember rightly) volts there are various versions of the system packaged as a separate motor or as part of the flywheel or torque converter running at engine speed, these systems can be used in a similar way to KERS in Formula one. But as this thread is about the P38 we are talking about good old alternators!
 
StuckAgainSteve said:
No, not monitored, as electrical load tries to pull voltage down, the (internal) regulator will increase output current until the voltage matches the fixed value the regulator is designed to output - it's as simple as that.
Click to expand...

So the voltage drop is recognised by the controller and the field voltage increased to compensate. The controller is monitoring the voltage drop and increases the field voltage to compensate. Same thing.
 
wammers said:
So the voltage drop is recognised by the controller and the field voltage increased to compensate. The controller is monitoring the voltage drop and increases the field voltage to compensate. Same thing.
Click to expand...

No, voltage is not increased to the exciter - current is. The term voltage regulator is a bit misleading. The only thing "regulated" is amperage required to maintain a given static output voltage assuming the current (in both senses of the term) load on the alternator is not more than its maximum output at the given engine speed.
 
StuckAgainSteve said:
No, voltage is not increased to the exciter - current is. The term voltage regulator is a bit misleading. The only thing "regulated" is amperage required to maintain a given static output voltage assuming the current (in both senses of the term) load on the alternator is not more than its maximum output at the given engine speed.
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Funny i was under the impression that field coil voltage was increased or decreased to strengthen or weaken the magnetic field to induce higher or lower voltage in the stator coils so as to increase or decrease the current or amperage output to the battery. Shows how wrong you can be.
 
wammers said:
Funny i was under the impression that field coil voltage was increased or decreased to strengthen or weaken the magnetic field to induce higher or lower voltage in the stator coils so as to increase or decrease the current or amperage output to the battery. Shows how wrong you can be.
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All I know is I've written the software to control the output of an alternator in an industrial generator setup, the "map" which dictated the output of the generator was based on the measured current (not voltage) put through the exciter fields, this was used to build a map of what's required to produce various outputs.
 
StuckAgainSteve said:
PS you may have been confused by the latest alternators which are controlled electronically, the exciter current is switched off during full throttle (assuming battery voltage is good) or bumped up to full amperage when the throttle is closed and the engine above target idle value (ie engine braking) there are new bosch systems which combine the function of an alternator and starter motor working in two modes 12 volt and 36 (if I remember rightly) volts there are various versions of the system packaged as a separate motor or as part of the flywheel or torque converter running at engine speed, these systems can be used in a similar way to KERS in Formula one. But as this thread is about the P38 we are talking about good old alternators!
Click to expand...
The special regulators I used to fit on boats were external microprocessor controlled devices.
The standard regulator controlled alternator takes may hours to fully charge the battery, as it's a constant voltage device the charge current diminishes as the battery voltage and thus the resistance increases.
The smart regulators were constant current (50 amps) for a timed period, temperature being monitored to avoid cooking the battery, reverting to constant voltage when the timed period was over. A normal alternator will charge at perhaps 80amps for a minute or so immediately after starting the engine, this rapidly falls away to an amp or so even when the battery is only half charged.
 
wammers said:
Funny i was under the impression that field coil voltage was increased or decreased to strengthen or weaken the magnetic field to induce higher or lower voltage in the stator coils so as to increase or decrease the current or amperage output to the battery. Shows how wrong you can be.
Click to expand...
Current and voltage are inter related V over R = I so if the field resistance is constant the voltage will be increased by the regulator to provide more current but it's the current that increases the magnetic field and thus increases the output current to maintain the output voltage at set point.
The battery is irrelevant, as I said earlier the alternator will work without a battery once it has started.
I used one I modified to produce AC which fed a home wound transformer with a 3 phase primary to suit the alternator and a single phase secondary.
Excitation voltage to the D+ was provided by a 6 volt dry cell lantern battery via torch bulb and a blocking diode, After starting the drive motor, a quick push on the exciter button was all that was needed to kick it into life. It was used for portable lighting so the fact that the frequency was way out didn't much matter.:)
 
Datatek said:
You did by saying that the battery voltage was monitored by the D+ line.
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D+ line acts as an earth path when ignition is in position three, then when current is detected BECM switches off charging lamp, starter is disengaged and D+ powers fuel pump. According to Land rover anyway. It would seem that all the alternators with battery voltage sensing did not require that facility. The controller on the two wire alternators is obviously different to the earlier ones. Perhaps the battery voltage sensing is built into it in a different way. And it just picks a signal up from the circuit it is built into.
 
wammers said:
D+ line acts as an earth path when ignition is in position three, then when current is detected BECM switches off charging lamp, starter is disengaged and D+ powers fuel pump. According to Land rover anyway. It would seem that all the alternators with battery voltage sensing did not require that facility. The controller on the two wire alternators is obviously different to the earlier ones. Perhaps the battery voltage sensing is built into it in a different way. And it just picks a signal up from the circuit it is built into.
Click to expand...

D+ does not power the fuel pump. The BECM switches the lamp off when the voltage from the D+ reaches battery potential and thus there is no current flow, the feed to the dash lamp only goes via the BECM so the BECM can detect a non functioning alternator, if the voltage from the alternator on the D+ does not reach battery voltage it aint working. It's the field windings via the regulator that acts as the earth path for the D+/dash bulb, current flow is from 12volts via the bulb to earth via the field windings, when power is being generated, the D+ has 12 volts from the stator windings which also feed the regulator, thus there is no current flow in the D+ line.
As said, some modern alternators have more sophisticated controls but we are talking P38.
 
Datatek said:
D+ does not power the fuel pump. The BECM switches the lamp off when the voltage from the D+ reaches battery potential and thus there is no current flow, the feed to the dash lamp only goes via the BECM so the BECM can detect a non functioning alternator, if the voltage from the alternator on the D+ does not reach battery voltage it aint working. It's the field windings via the regulator that acts as the earth path for the D+/dash bulb, current flow is from 12volts via the bulb to earth via the field windings, when power is being generated, the D+ has 12 volts from the stator windings which also feed the regulator, thus there is no current flow in the D+ line.
As said, some modern alternators have more sophisticated controls but we are talking P38.
Click to expand...

D+ Pulls the pump relay in. It is spliced into the line that feeds pin 15 on BECM.
 
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wammers said:
D+ Pulls the pump relay in. It is spliced into the line that feeds pin 15 on BECM.
Click to expand...
I'll give you that one, I have two drawings one shows it one does not. There are 3 pull ups via diodes for the fuel pump relay, D+, Starter relay and one other that seems to have no I.D., must look at that a bit further
 
Datatek said:
I'll give you that one, I have two drawings one shows it one does not. There are 3 pull ups via diodes for the fuel pump relay, D+, Starter relay and one other that seems to have no I.D., must look at that a bit further
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Pre 99 only two D+ and glow plug 6. After 99 starter relay. Tired of arguing Keith as long as the bloody thing works i don't give a toss how it does it. :):):)
 
wammers said:
Pre 99 only two D+ and glow plug 6. After 99 starter relay. Tired of arguing Keith as long as the bloody thing works i don't give a toss how it does it. :):):)
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I will always defer to your superior knowledge on FIPs, valve blocks etc but electrics has always been my metier:):):)
 
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