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Old 05-22-2008, 02:05 PM   #1
MrBill
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Default Alt Exciter wire

Okay my voltage in my car is... abysmal. Battery reports 13.3-13.5, not bad. But the fuse panel delivers a smoothe 11.2-11.5. Alt is 80 amp ND. Problems were the same with another alt.

Now, EVERYTHING goes through the fuse panel in my car. Megasquirt and its components (LC-1 in particular) do not like this low voltage. LC-1 wont even work with the lights on.

Until I get the wiring fixed, I am wondering exactly how the exciter works. Does it just deliver 12 volts to my alternator? Or is it more-special than that?

If I were to disconnect the exciter wire and give it battery voltage (2 volts higher) would it deliver more, or less power? Does the voltage regualtor try to make X volts or need X volts to make power?

What about a big resistor in line to the exciter wire? So then it might put out higher voltage?
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Old 05-22-2008, 03:19 PM   #2
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The exciter does just that..get things going by building an initial field up. The internal regulator is what sets the charge voltage. Have you already checked (by means of a voltage drop test) to see that both your power and ground cables from the battery are still in decent shape? I've had em corrode inside so they LOOKED good but were dropping the voltage quite a bit.
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Old 05-22-2008, 07:32 PM   #3
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have you checked voltage drop to your fuses? that would be easier than cheating the system. how are your fuse connections? cruddy/brown lookin? did you do the voltage drops over your fuses? anything over .03 volts is above ase spec, my teacher is more realistic and says .05v is ok- need to think how long the wires are as well. check the junction block close to the battery, watch drop there. and even the terminal on the battery, its a numbers game. if you drop .05 from the top of the terminal to the junction block, that will mean you lose .05 volts through every circuit in your car that goes through the junction block
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Old 05-22-2008, 07:41 PM   #4
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on my car the alt. wouldn't put out anything....fixed the bad alt to chassis ground, still nothing.....put 12vdc directly to Field and bam!!! plenty of juice....if connected for too long, good chance of overcharging the battery !!!

in my case, bad bulb in the dash to complete the circuit....
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Old 05-23-2008, 06:59 PM   #5
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I have a fault somwhere in the exciter circuit, so I just disconnected it. Alt kicks on around 2k RPMs and stays on, sometimes it can be a bit finnicky if its cold and she's been sitting for a while, but now that I'm drving her daily it always kicks on as I pull out of the driveway.
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Old 05-30-2008, 12:34 AM   #6
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so no one really answered the question,

can I "lower" the exciter voltage via a resistor and make the alternator charge at a higher voltage?
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Old 05-30-2008, 04:05 AM   #7
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instead of half assing it, just fix it right. less brain activity.
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Old 05-30-2008, 05:02 PM   #8
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I suspect the exciter as my source of charging issues as well.

had the battery checked, replaced the alt, then had the rebuilt checked as well, all ok.

barely getting any charge from the alt to the battery.

I ran an additional wire from the hot side of the coil to the alt where the exciter wire lives, and when connected the voltage comes right up.

the problem is that if I leave this additional wire from the coil to the ALT connected - the car won't shut off.

I have to pull my extra exciter wire to stop the motor from running when the key is out of the ignition.

would this bypass work ok and still allow me to turn the car off if I just totally disconnect the stock exciter wire, or will it make the car continue running anyway?

thanks
cr
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Old 05-30-2008, 05:14 PM   #9
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Default exciter circuit

No, in answer to your question. Changing the resistance of the exciter wire circuit won't affect the charging voltage. It's purpose is twofold. One to provide the exciter voltage to stimulate the alternator to charge. Then if the alternator fails completely that circuit is grounded through the alternator to warn you it isn't charging. When the alternator charges it's voltage matches what is on the battery at that terminal which makes the warning light go out.

If you are using a Bosch alternator with the external fan then Dave Barton and other parts suppliers did have an adjustable voltage regulator for a very reasonable price.
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Old 05-30-2008, 05:20 PM   #10
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Default exciter wire

Quote:
Originally Posted by airkooledchris View Post
I suspect the exciter as my source of charging issues as well.

had the battery checked, replaced the alt, then had the rebuilt checked as well, all ok.

barely getting any charge from the alt to the battery.

I ran an additional wire from the hot side of the coil to the alt where the exciter wire lives, and when connected the voltage comes right up.

the problem is that if I leave this additional wire from the coil to the ALT connected - the car won't shut off.

I have to pull my extra exciter wire to stop the motor from running when the key is out of the ignition.

would this bypass work ok and still allow me to turn the car off if I just totally disconnect the stock exciter wire, or will it make the car continue running anyway?

thanks
cr
What I suggest you do is to repair the stock exciter wire circuit which is controlled with your ignition switch. I would test the exciter circuit by grounding the small red wire at the alternator. If the light comes on the dash it's functioning. If it doesn't you either have a bad bulb or a break in the wiring. Depending on what year your car is you may have some wiring harness issues that also need attention. On my 93 the idiot light wire developed a break in it on the engine. So, I ran a new wire along the firewall tapping into the harness before the break. Then I ran the wire along the firewall to the right side inner fender and connected it to the alternator. I ran it forward along the inner fender till it was just opposite the alternator. Then I ran the wire to the alternator and the circuit has worked fine ever since.
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Old 06-01-2008, 03:25 PM   #11
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So, I ran a new wire along the firewall tapping into the harness before the break. Then I ran the wire along the firewall to the right side inner fender and connected it to the alternator. I ran it forward along the inner fender till it was just opposite the alternator. Then I ran the wire to the alternator and the circuit has worked fine ever since.

I pulled the stock exciter wire and grounded it, no light on the dash. the bulb is ok as it does turn on when the key is on and the car hasn't been started.

so I guess it is busted somewhere along the line.

little confused on your steps tho.

you basically just swapped it out with a new wire all the way over to the starter?
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Old 06-01-2008, 04:44 PM   #12
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Default charging light

If your charging light is coming on with the key then the circuit is working fine. You must not have had a good ground when you grounded it to check it. I've had that happen. You must be sure that it's a clean good ground. A good spot to use is to use an alligator clip lead and connect the wire to the braided ground wire on the valve cover.

My break in the charging light wire was along the side of the engine or under the crankshaft pulley where the stock harness runs. So, I cut into the stock harness before the break where the harness runs along the firewall. Then spliced into the charging light wire and ran this along the firewall, then inner right fender till it was across from the alternator and ran the wire down to the alternator. When I meant opposite it meant where the right inner fender is in line with the alternator. I ran the wire from the right inner fender to the alternator. Nothing to do with the starter or the starter side of the engine.

PS Left and right side of the car is from the drivers perspective.

Last edited by dl242gt; 06-01-2008 at 04:45 PM.. Reason: add PS
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Old 06-02-2008, 01:15 PM   #13
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I ended up running a brand new wire through the firewall from the exciter position on the back of the ALT to the 4th spade up from the bottom on the fuse panel, which is where I *think* the stock one is located (from the ****ty manual I have that looks to be the one)

this works to bring the charging voltage up to where it should be, however I can't shut the car off then and only the parking break light and the oil pressure warning lights work anymore.

disconnect my extra exciter wire, the charging voltage drops again, and the warning lights all work properly.

the only thing I could think of to get proper charging rate and still be able to turn the car off was to run a relay to another switched source so when I turn the key off it kills the connection to the exciter wire and then the engine will actually kill.

I think there is some underlying wierd electrical issue and im not sure im qualified (I just laughed as I said that to myself) to find and repair it. my buddy is a really good car stereo installer and works around these electrical issues from time to time and he's just stumped as well, which means im totally in the dark.


I have a feeling though, that if anyone knows why the exciter wire connected to the stock spade on the fuse block makes the car continue to run when the key is out, that should explain the random results im getting here. Note also that it does the same thing if I just run the wire straight to the hot side of the coil as well. it brings the charging voltage up just fine, but the car wont turn off then and my warning lights stop working.
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Old 06-02-2008, 01:25 PM   #14
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Default exciter wire

No offense but I don't understand why you won't just wire it up to the stock position? If you ran a new wire you should splice it in to the dash cluster wire for the charging light.

The most likely reason it stays running is a bad wiring harness on the engine.
If you have a bad wiring harness that means various wires are shorted together and the alternator still has a complete circuit when you turn off the car. My friends 240 turbo had just such a problem. The wiring harness was so bad, with so many wires shorted together that the car would start fine but when you turned it off it kept running until you pulled of a coil wire.

Either that or you are completing the circuit so the alternator keeps the car running.
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Old 06-03-2008, 06:02 PM   #15
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Originally Posted by dl242gt View Post
No offense but I don't understand why you won't just wire it up to the stock position? If you ran a new wire you should splice it in to the dash cluster wire for the charging light.

The most likely reason it stays running is a bad wiring harness on the engine.
If you have a bad wiring harness that means various wires are shorted together and the alternator still has a complete circuit when you turn off the car. My friends 240 turbo had just such a problem. The wiring harness was so bad, with so many wires shorted together that the car would start fine but when you turned it off it kept running until you pulled of a coil wire.

Either that or you are completing the circuit so the alternator keeps the car running.
the harness in question is the small grey box mounted to the firewall, just about dead center yea?
is there a good map of whats what in this harness in one of the available manuals? my hanes seems to be missing good detailed descriptions of whats what here, or even a simple map of whats what when your looking at the fuse panel inside the vehicle.
does the bentley go deeper into that stuff?
and is there a web based version of the bently, or a dealer software program one can use to look up these details? (that I might be able to 'source' in the usual 'you shouldn't have this program' areas?)

thanks,
Chris
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