Alternator charge start.

[tedshark]

On my truck I have always had to rev the engine up for the alternator to start charging.
Anyway I have been OK with this, but now I have to rev the hell out of it before the charge light goes off.
What controls when the alternator starts charging?
Anyone else experience this problem?

[82vdub]

I believe it's a rectifier circuit or something like that inside the alternator. If it's taking a while to start charging, it's probably on it's way out. You can remove the alternator and bring it somewhere for someone to test it.

[VWCaddy]

Might clean up the connections for the blue exciter wire. That is what feeds current from the charge LED to the alternator windings to start it charging. Without that connection, it will self-excite, but that takes the higher RPMs.

[zman]

The few times that happend to me I replaced the regulator to fix it. It`s that unit on the back with the two screws holding it in. It tilts out after the screws are removed, contains the brushes also.
Funny thing is I have never had anything else fail with my alternators.
Battery disconected of course.

[tedshark]

Ok, I replaced the voltage regulator and did not take care of the problem.
Any other ideas, I need an electric print then maybe I can figure this out.

[Quantum-man]

Do as Roger says and check through the blue exciter wire up through to the instrument display.
I would say that
1) It's as common an occurance as cracks between valves

2) My alternator has been doing it since I bought the car in 2005, and if it's 'on it's way out' then it had better hurry up before the rest of the car dies

[FineFrank]

Anyone else experience this problem?

I've had the same problem. I wasted plenty of time doing different things, but it ended up being a bad "blue" wire. Fixed it, and it was fine.
What year truck do you have?

[Quantum-man]

Anyone else experience this problem?

I've had the same problem. I wasted plenty of time doing different things, but it ended up being a bad "blue" wire. Fixed it, and it was fine.
What year truck do you have?

Hi Frank,
Where was it 'bad'?

Mark

[tedshark]

Anyone else experience this problem?

I've had the same problem. I wasted plenty of time doing different things, but it ended up being a bad "blue" wire. Fixed it, and it was fine.
What year truck do you have?

My truck is an 80, you guys are talking about possible problem with the blue wire that runs from the indicator light to the alternate right?

[tedshark]

OK I cut the blue wire and the light goes out, so what could possibly be wrong with the wire?
This blue wire is supply power to turn the light out?
If this is the case then this does not start the charging.

[VWCaddy]

OK I cut the blue wire and the light goes out, so what could possibly be wrong with the wire?
This blue wire is supply power to turn the light out?
If this is the case then this does not start the charging.

Blue wire/exciter circuit basically runs from the battery to the charge LED on the dash then to the alternator. At start, the battery connection feeds current through the LED to the alternator to supply the initial magnetic field to jump start it, so to speak. Once the alternator voltage rises to match the battery, the charge LED has 12 volts on both sides resulting in no current flowing and the LED turns off. Logically cutting the wire will also cut off the current and the LED will go off. However, a poor connection of the blue wire may allow enough current to flow through the LED to illuminate it but not enough current to make the alternator fire up. The LED takes a few milli-amps to light up, the alternator probably needs a fair bit more. Usually there is a bit of residual magnetism in the rotor to finally start the alternator charging given a high enough RPM, at which point the charge LED goes out by itself.

[hagar]

tedshark asked : " What controls when the alternator starts
charging?"

Here is hagar trying to simplify a very complicated issue.. : "VW-Alternators" .

This information is NOT tedshark specific. it is aimed at all Newbies .who IMHO will have to face the music sooner or later.

First : tedsharks problem is simple to fix ., a simple doorbell butten to start the charging. No need to speed up engine..
or smaller pulley on alternator or bigger pulley on crankshaft.(there are 2 different from VW 1.5 L and 1.6 L ).

Back to Alternators : all VW alternators are 3 phase about 400 HZ . followed by a 3 phase full wave bridge rectifier. (6 Diodes) Read 82vdub and VWcaddy and all the others . note: if you have a real crazy problem bounce it of Mark Shepherd aka Quantum-man..

With 6 Diodes could the loss of one Diode be a problem ? YES.

VW use two makes of Alternators BOSCH and Motorola. I like both..

NO we can not ruin by overload , alternators are self protected by Impedance , a Generator can be overloaded.

Sliprings and Carbon brushes must be attended to Field is a simple one coil (spool?) with many pole pieces. I forget how many but lets say 4 south and 4 north . That is how 400 HZ comes about.

Can a newbie test the Diodes ? YES with help from the forums. , I will gladly name the Alternator experts here. Roger Brown and Sandy Cameron (Dans) there are many more Vincent maybe ?

How do we name experts ? if we are not one ? BUT hagar is.

hagar.

[hagar]

This to follow is not for newbies on alternators., BUT it is part of an answer to tedsharks question What controls when the alternator starts charging?

My darling "Ducling" does exactly like that , to turn the led off I blip the pedal after that all is fine..

Will the alternator start charging and turn the red led off ? at idle ? Yes it will . (Push button) connected to Battery plus and Positive slipring connection. (Simple to do),

Alternators do put out voltage from residual magnetism BUT not enough to overcome the Silicon Diode junction drop 0.2V?
Germanium junctions are 0.1V? we are not dealing with OHM's law it is not a I R drop.

On a Rabbit the RPM is also involved. .

SO ? what do we do here at hagar's we test all 6 Diodes. . some Motorola jobs have a BIG diode in wire to Battery.

hagar.

PS : before all this we test Sliprings and Brushes (two). A proper test of the alternator is complicated it requires a load test. .At full load for say 8 hours.

[tedshark]

Will the alternator start charging and turn the red led off ? at idle ? Yes it will . (Push button) connected to Battery plus and Positive slipring connection. (Simple to do),

Continue, and explain.

[hagar]

tedshhark and all , the alternators is a lot of fun . Once you understand how they work.

Yes they will put out 120 Volt DC no problem . SO ? they will power your 1/4 inch drill , no problem or a light.

or charge a battery at full charge. I use to charge Nicads at 60 Amps at idle . 12 volt on field. Motorola Taxicab Alternator. What for ? Fishing with electric outboard..

Those were my better days , Land Rover in the BC wilderness. . hagars "Safaris" .

"Safaris" ? yes British Columbia is Safari country class a 1. I hope you all get that experience..

hagar