LT Texan

I don't know much about auto voltage regulators, but I know a bit about the voltage regulators I build for my hifi power supplies. And these always have 3 connections, input output and reference voltage.

These voltage regulators try to keep output voltage at a fixed value above reference voltage (1.25V for the ones I use - no idea for an auto application).

I always thought that was what the small terminal lead did - give the voltage regulator a reference voltage based on a resistor voltage divider circuit (which is what I always assumed the resistor and light in the pod were).

So, I would expect the small lead on the alterator to always be a voltage less than the big lead.

With the car running, is there a difference in voltage between the big and little terminals on the alternator?

Am I way off base for an auto application?

Edit: Or maybe not. I'm going to take a look at the current flow charts when I get home. I bet the small terminal connects a reference voltage to the voltage the battery sees across the parallel light/resistor. That way when the voltage on the battery drops lower than the reference voltage current flows across the light/resistor illuminating the idiot light. I bet all the other crap I wrote above is contained within the alternator.

IndyMatt

Thanks guys, I will reference this thread when I get back to the states in December. I am currently in Iraq as a DoD civilian. I can't do anything right now other than possibly answer questions on what I have already done. I have looked at the 14 pin connector wiring as well as pulling the back off of the connector to inspect the wires. There was one wire that had the insulation cracked and ALL were very brittle. i did repair the one wire that had an obvious problem, it didn't solve the problem. It might be a good idea to replace the wiring harness due to the fact that all of the wires I have looked at are not in the best of shape. As far as tracing wires, I am confident enough to due this with guidance.

This problem happened after I did the timing belt on the car. So it was after I removed the wiring harness and dropped the alternator. Another reason I think it may be a broken wire somewhere.

The thing that baffles me is that the low voltage idiot light comes on when I ground out the small terminal but it NEVER came on when driving and the voltage dropped low enough for the car to stop running. Any ideas?

I thank you guys for all your help so far.

Landseer

Intermittent and partial connections can create all kinds of havoc.
What we can do is trace the diagrams for you and provide a step by step set of wire test instructions. BTW, there exist online diagrams here if you have time to view them. http://www.cannell.co.uk/Manuals.htm
That's how I've tracked down many problems, combined with (lots of) help from the experienced guys here.

You can install the alternator, for instance, sans cover.
Piggyback a test lead on the hot terminal and the exciter terminal and a third lead on an engine bolt as a ground.
You can start the car and read the voltages on the test leads.

Other easy ways exist to trace the wires to and through the panel, even the pod. Should be ultimately an easy fix. Stay safe.

blown 87

For what it is worth, I cant tell you how many times I have fixed charging systems on cars that the alternators have tested good on the bench by replacing the alternator.

WallyP

If I were in this position, I would try to find a good auto electrical shop - not a standard repair garage, not an Autozone, but a shop who specializes in repairing and rebuilding alternators, starters, and generators.

I would take them the alternator, and talk to the owner or the head shop guy. I would ask them to rebuild the alternator for higher output, including using a regulator that has higher-than normal output when it is hot.

There are at least five or six different regulators that will work in our alternators. One of the differences is that most of them cut the output voltage when the regulator is hot. In most cars, the battery is in the engine compartment. When it is hot, it needs less voltage to fully charge, so the regulators cut back to prevent battery damage. Our batteries don't get hot, so we need the higher charging voltage.

By getting YOUR alternator rebuilt, you know that it is correct for the car and that it will fit. The cooling cowl will be there and will fit, the wiring connectors will be correct, etc.

Alan

Missed this a few weeks ago while on vacation...

Yes you are way off base here.. from a purely practical perspective it really isn't anything like that...

The terminals on the back of the alternator have quite different functions. Your theory is not far wrong for general regulator operation but those signals are internal and self contained in this circuit. The exciter circuit really has notihng to do with the voltage regulation reference point.

The big teminal is the output of the alternator and connects directly to the battery. When the alternator is not generatiing it sees permanant battery voltage. When the alternator is generating it sees whatever voltage it can generate over the battery voltage. During normal operation the voltage regulator is self powered by the alternator and attempts to regulate to a reference voltage of ~13.5v.

The alternator cannot normally generate any low rpm power without both rotation and some current flowing in the rotor windings (connected to via brushes & slip rings). The ignition fed excitation circuit (61/D) is what provides this initiation current via the (no) charge light and bias resistor. Once the alternator starts generating the operating rotor current is then provided by the stator windings of the alternator via the voltage regulator and also feeds back to the exitation circuit - the charge light goes out as the voltage across it is equalized.

The regulator controls rotor winding current to manage voltage & power generation.

There are actually 3 alternator connections:

Output (30/B+) - Directly connected to the battery and all 'consumers' in the car
Initiation (61/D) - Connected to ignition (15) via the (no)charge bulb & parallel bias resistor
Ground (31) - Provided by the case bolting to the block.

There is no individual regulator input - in this case the input is internal from the 3 phase stator windings (120 degree star or delta) of the alternator fed via 3 dual diode banks directly to the (30/B+) output terminal.

The phase outputs must also be grounded via opposed diode pairs per phase.

The regulator controls alternator voltage generation - it is also supplied by the 3 phases via 3 seperate feed diodes. The regulator monitors the 30/B+ output against its internal voltage reference set point and controls the rotor current to regulate power generation.

As you can see the charging of the battery is quite direct - it will charge at a rate based on its current state of charge and the the alternator output voltage. There are no real smarts involved - the higher the voltage the alternator can generate the higher the battery charge current can be.

Alan

IndyMatt

Okay, so I know this thread is almost 4 years old. I haven't touched my 928 in quite a while but I still have this issue.

I am going to make a list of what I know to be true:

1. Took alternator to an auto electronic shop. Verified good, ran at speed, with and without a load, as well as on a separate tester with a ripple tester to test diodes. Everything was fine.

2. Exciter wire-12v with ignition on, with the wire grounded lights light up like a Christmas tree (all of them)

3. Tested alternator in the car with all car wiring disconnected, ran it up using jumper wires from exciter post to battery and output on my DVM and it was generating.

4. The minute wires were connected, nothing.

5. With all the wires connected normally to the alternator, no test bulb like when the exciter wire is grounded when key is turned to on. This includes no low voltage light on the dash meter.

I am at a total loss! I am going to go freaking nuts I swear. Is possible that there is something on the B+ side downstream that is causing issues?

Please help.

Paul Dortkamp

The only way you are going to solve this, is by doing/changing one thing at a time and testing. Starting at point zero.
Every wire and connector is suspect. So only connect one thing at a time then test. Then connect another then test. Repeat this is the only way. How do I know this? I had a similar issue which turned out to be a faulty crimp in an eyelet that was invisible to the naked eye.

Buy a fresh battery, charge up. Be careful you will have a lot of loose wires that are not insulated or fused.
Disconnect all factory wiring from starter, alternator and battery. Insulate all ends both + & -
Place battery on ground under car. Connect - to engine block. Connect + to 30+ at starter motor. Connect a suitable wire from + on starter to + on alternator.
Connect a globe to d+ to + on alternator.

Start engine and measure running voltage at alternator.

If this works then work backwards to the battery in the rear.

Reattach normal connection from Alt B+ to Starter 30+. Test running voltage at alternator.
Put battery in normal location. Reattach + & - . Test running voltage at alternator.
Then move forward.
Reattach red 10mm2 wire to Alternator B+; If it has 2 wires to the eyelet, Disconnect other end from jump start post and wrap safely. Test running voltage at alternator.
Reconnect other end from jump start post. Test running voltage at alternator.
Disconnect temporary lamp from D+, Reconnect D+ wire at alternator. Test running voltage at alternator.
Somewhere along this chain you will isolate the faulty wire/join/fitting/broken cable inside/dud item

Alan

Are you realy sure you are connecting the small connector correctly when its installedin the car?

You say above that the exciter circuit works correctly without the alternator connected, with ignition on the (60) wire is at 12+v at the alternator end and that if you ground the (60) wire at the alternator end you get the charge warning light on.

That you don't when the alternator is installed suggests you have connected the (60) wire to a permanent battery (12+v) connection.

Try the alternator in the car - with a jumper lead directly to 12v connected to (60) just as you did with it out of the car (make sure its the same exact connecting point that worked before with it out of the car).

This is something simple....

The only other possible option I can see that fits the symptoms you describe is that it actually does work in the car, but doesn't realy connect to anything (this would require that the charge light come on in bulb test /pre start at least??).

It's possible the connection from the jump post to the alternator is almost non existant - not completely open circuit but poor enough that you can sustain a large voltage drop across it. For this to be possible someone would have had to have already modified the original wiring so its a long shot... You could test for this by directly monitoring the voltage at the B+ terminal on the alernator while runing

So mostly I still think you may be bolting the small terminal to the wrong thing...

Alan

IndyMatt

I am positive that the exciter wire is connected correctly. It has zero voltage when the ignition is off, with the key turned to on, it has 12V. So that indicates that it works. The charge light (as well as all the other warning lights) does come on when the exciter wire is grounded and the key turned on. I get 12V with the ignition on when connected to the alternator as well.

I truly believe there is a connection issue on the B+ terminal/circuit that may be connected wrong or something. I plan on taking pictures of all connections and posting them so that you guys can see what I am seeing and if there is an issue. I think there might be an issue with the connection between the battery, starter, battery. I need to make sure that there is continuity there. I have mostly focused all of my attention towards the exciter circuit and whether the alternator itself was good or not.

There are two things here, one is that with the all of the cars wires connected to the alternator known of the warning lights come on when the ignition is switched to on. Should all of the lights come on like when I ground the small wire? So when I ground the small wire the low charging light comes on with all of the other warning lights such as the oil pressure light and all of the others. However when that small wire is connected to the alternator and the ignition switched on known of these warning lights are on before turning the ignition to start. Basically there is no bulb test mode right now when the ignition is in the on position. Not sure what that means but I am sure that that is connected to this issue somehow.

I can tell you right now that there is voltage drop between the jump post and the battery and between the jump post and B+ terminal. It is amounts to about half a volt, basically the jump post registers just over 12 volts on DVM, when I connect it directly to the battery it registers about 12.5-12.7. I just figured that was resistance caused by all of the wire and connections between the jump post and battery.

The main reason I think that the problem is within the B+ circuit is this:

1. I started the car with just jumper wires to both terminals. I connected the small terminal of the alternator directly to the batttery, then checked the voltage on the B+ terminal and the alternator was generating just fine.

2. Left the wire connected directly to the positive terminal of the batter, connected the large guage battery wire to the B+ as it should. Nothing, no generation, just battery voltage when checked at the B+ terminal with my DVM.

3. So with all of the test checking out on the exciter circuit side (12V with ignition on, low charge light on when grounded) as well as this last test it tells me that there something connected wrong somewhere on the B+ side.

I am just at a loss right now. I will be checking the B+ terminal next. I will try to take some photos later today/tonight. I will get a picture of the back of the alternator, starter, and the jump post area with the 14 pin connecter, is there anything else that I should get a picture of? Kind of busy this week so it might take another week or so to really dig back into this beast.

Alan

This is wrong - it should only be about 1-2v when connected to the alternator and the engine is not running. Again I think your exciter circuit is fine - but I don't think it is connected to the right terminal on the alternator - I still think this is it. It should not be at 12v when it is not rotating. This is why your bulb check doesn't come on. check again.

Whatever terminal you are using now - what is its voltage when the exciter wire is not connected? what other terminals to you have? what kind of alternator is this?

Alan

Mrmerlin

something else to consider along with Alans great suggestions is the fact that,
if this alternator has ever been suspended on its harness,
there is a good chance the blue wire has been damaged ,
this will happen at about 4 inches from the the end of the wire inside the orange sheathing, the blue wire shears off and its hard to find this unless you know where to look.

Test this blue wire disconnect it from the rear of the alternator and see if it has continuity to the 14 pin connector maybe its shorted to another wire in the bundle.

All this being said before you do anymore testing ,
please post pictures of the rear of the alternator,
and remove the brush holder and take a picture of it as well,
and post them,
working in the dark isnt any more fun for a diagnoser as it is the diagnosee

IndyMatt

Alan I tried to answer your questions above, again I appreciate everyone's help.

IndyMatt

I have checked the wire out and it is fine based on when grounded the low charge light is lit and it tests at 12V with the ignition on.

Alan

You said (above) : I can only work with what you tell me. In context the above seems to mean the exciter wire is connected to the small terminal and with ignition on (presumably not running?) you say you have 12v on that terminal - this cannot be correct... and would explain why you don't get a bulb check.

If this is NOT actually the case (as you also say...) - and you have <1v on the exciter terminal with ignition on (engine stopped) - then the bulb check should be on at that time.

Honestly its getting too confusing here. I'd suggest you add pigtails to both terminal off the back of the alternator so you can monitor (61) exciter and (30) B+ on the alternator remotely while changing conditions.

This is what you should get:

........ Ignition off | Ignition on engine stopped | Engine running
==========================================
(61) 0v | ~ <1v | ~13.5v
(30) 12+v | ~12+v | ~13.5v

This will tell you for sure what the 61 terminal is doing and will also tell you if the alternator B+ (30) is doing something different to the Jump Post. This will help evaluate your concern on B+ connection also.

Alan