another alternator question

[vtrich]

My question relates to my 1970 911t.

I'm trying to figure out why my alternator light is staying on. I have read many posts and thanks to those, I think I understand how the light works. I just can't figure out which way the power is flowing to make the light stay on all the time.

I have tested the battery with the engine off (12.6) and tested the battery with the engine idling (12.5) and tested with the engine at 2000+ rpm (12.5) and I have had my lovely helper turn the lights on and put the highs on also and each time the reading stays around 12.2 or so.

In reading various posts on the electrical system and it seems I'm not getting enough juice to the batteries or I'm getting the absolute minimum but I was thinking it wasn't so far off that the light would at least flicker, but it stays on full bore.

Do my voltage numbers seem too low, and if so, would that indicate an alternator not capable of producing enough juice? I'm guessing the regulator is functioning but then I'm not sure if the alternator is not putting out enough.

The initial reading is taken shortly after I disconnected the battery tender,...so maybe the batteries are simply loosing juice.

Any ideas as to why the alternator would be glowing constantly? Other than to simply annoy me.

THANKS!!

Rich

[M_deJong]

Rich, it seems your alternator is not producing voltage. The light is on when the alternator field coils are being supplied voltage from the battery (thru the ignition switch and voltage regulator). Once running, the alternator generates enough current/voltage to self-energize and no longer needs help from the battery. The light goes out because there is +12V (or more) on both sides of it, so no current flows thru the bulb.

In your case the alternator is never self energizing. You should see 13.5- 14V at the battery with the engine at 2000 rpm. You aren't seeing any more than battery voltage. Your battery/ies are strong enough to run the car for a while but eventually will die, and then no more fuel pump and ignition.

Most likely cause is a shorted diode in the alternator - easy repair if you have a good alternator shop or some skill with a soldering iron. Could also be a bad voltage regulator. VR is easier to change but less likely (imho) to be the cause.

Mike

[vtrich]

Mike, THANKS for the reply,...makes good sense. I'll pull the alternator,...send it off to get
checked/rebuilt.

Rich

[ESully]

With the engine running you want to see about 13.8V, at around 1500rpm or higher.
When the key is turned on, engine not running, you should read battery voltage to ground on the R/Bk wire, blue D+/61 wire and the black DF wire. If no reading on the R/BK problem at ignition switch, it is not fused. If no reading on the blue wire, lamp is burned out or internal connection from lamp holder to R/Bk is bad. If no reading on black wire to ground the contact is open in the regulator. Bad regulator. Without power on the black wire then the alternator cannot produce power. If the voltage is too high then the contacts are staying closed too much. The battery power on the red wire will not pass through the alternator because the diodes do not allow it to travel in that direction.

Basics. Key is turned on, Power from ignition switch to R/Bk feeds gages. Indicator lamp is tied to R/Bk inside gage, power goes through 2 watt indicator bulb to blue wire feeding D+ on regulator. Since alternator is not spinning to produce voltage, lamp lights up due to voltage difference. Power flows through regulator out to DF to Alternator DF. Power energizes (excites) field in Alternator which creates magnetic field.
Alternator spins, rotating magnetic causes AC power to be produced in stationary coils, and the diodes which only allow current to flow in one direction convert it to DC. Voltage is now provided to B+ and D+. Regulator is set to open contacts when voltage exceeds set point to stop power, closes when voltage drops. Output of D+ is now equal to Voltage on R/Bk so there is no longer a voltage difference causing lamp to go out.

[vtrich]

I'm sorry for the delay, but, well work's been busy.

I got the alternator out and am going to put in the Valeo until the old Bosch gets rebuilt.

But, first, there is only the heavy woven ground from alternator body to engine. Most pictures I've seen
show a smaller brown ground wire from the harness, I don't have one. The only brown wire I can find
Is bundled with the black wire which gets left disconnected. Is this a problem?

Second, it appears the blue wire goes from the alternator to the regulator but the regulator will be disconnected
so what do I do with the blue wire at the alternator?

Sorry for all the questions, just want to have a general understanding,...and not screw it up.

THANKS!!

Rich

[M_deJong]

Lets see if I understand. You are going to substitute an internal regulator Valeo for your external regulator Bosch, and you need to adapt the wiring?

[vtrich]

Hi MIke,

Yes, that is the plan. I have read as much as I can find and feel I understand the wiring on the back of the alternator.

I'm just not clear what to do with the wires that were attached to the external regulator? Specifically, the blue wire appears
to connect the alternator with the ignition switch but if I disconnect the external regulator that would leave that connection
broken. I'm wondering what people do with all the wires that attach to the external regulator?

Maybe this was just a bad idea. It will take a week or more to get the Bosch unit rebuilt,...so I was just hoping to get it
on the road.

Also,....my car had the white plastic housing surrounding the alternator. Most of the pictures I've seen don't show that
so I'm also wondering if folks just leave that off? It does appear to serve a air funneling purpose.

THANKS for any advice,..I really appreciate the help.

Rich
piece.

[ESully]

Here is an article on the conversion to internal regulator.

[304065]

Rich,

Disconnect the battery before doing any electrical work or you can suffer personal injury or property damage.

Now then-- the original, externally regulated alternator has four connections:

B+ battery positive, fat red wire to starter terminal, and you should also have some smaller red wires to the 14-pin connector.
D- ground, this is a brown ground strap from D- to one of the bolts on the engine case parting line. Also some smaller browns to 14-pin.
D+/61 blue wire. This is used for excitation of the field and for feedback to the voltage regulator. It is the most important wire in the car.
DF Dynamo Field-- this is a black wire from the VR to the positive brush for the field. This is how the field gets energized.

Now, an internally regulated alternator such as the modern Valeo does not use DF. As such, you can tape off and safely tie the black wire out of the way. You remove the plug from the VR over on the engine electrical console and you are done.

This was originally described by the factory in a service bulletin posted long ago by our departed friend Warren Hall, Jr. "Early_S_Man"



And YES you should put the air guide back in place, it will keep the wires off the engine and helps divert air to the cylinders. If yours is original you will need to cut the bottom of it to fit around the Valeo's VR most likely.

[304065]

LOL Mr. Sully great minds think alike!