voltage at alternator posts
07-19-2006, 02:27 AM
#1
Track Day
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voltage at alternator posts
I DO have an engineering degree. I am NOT an auto mechanic... but I am GOING to solve this electrical problem!!!
There are two electrical posts on my alternator. After a ground point cleaning, the stator? (big post) is at battery voltage.
The rotor? (small post) is disconnected with the ignition OFF and with the ignition ON (engine stopped) it reads two or three volts. Somebody tell me thats wrong.
On the current flow diagram, the wire ends at X38... after passing through T14 and O8. Well THAT helps me alot. Is there another section of the books that defines all these codes? Is that horizontal line that spans the whole page supposed to be a +12V bus?
There are two electrical posts on my alternator. After a ground point cleaning, the stator? (big post) is at battery voltage.
The rotor? (small post) is disconnected with the ignition OFF and with the ignition ON (engine stopped) it reads two or three volts. Somebody tell me thats wrong.
On the current flow diagram, the wire ends at X38... after passing through T14 and O8. Well THAT helps me alot. Is there another section of the books that defines all these codes? Is that horizontal line that spans the whole page supposed to be a +12V bus?
07-19-2006, 10:23 AM
#2
Gluteus Maximus
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1. You must post what model year you're talking about if you want any decent help.
2. https://rennlist.com/forums/928-forum/209899-workshop-manual-elect-schematics-anyone-need-usage-notes.html
3. The horizontal lines across the top of the pages are the major buses (ground, switched 12v, constant 12v, etc.). The continue from one page to the next. They are also labeled. If you're no sure what bus you're dealing with, follow it to the other pages until you see where it gets its power (or ground) from.
4. T14 and O8 - most likely T and O are the plugs and 14 and 8 are the pins in those plugs. If you look at the bottom of you fuse/relay panel there's a row of plugs. These are lettered starting w/ A at the left (look closely and you'll find the letters).
5. If you post a copy of the page (or part of the page) you're talking about, I'd be able to help more.
2. https://rennlist.com/forums/928-forum/209899-workshop-manual-elect-schematics-anyone-need-usage-notes.html
3. The horizontal lines across the top of the pages are the major buses (ground, switched 12v, constant 12v, etc.). The continue from one page to the next. They are also labeled. If you're no sure what bus you're dealing with, follow it to the other pages until you see where it gets its power (or ground) from.
4. T14 and O8 - most likely T and O are the plugs and 14 and 8 are the pins in those plugs. If you look at the bottom of you fuse/relay panel there's a row of plugs. These are lettered starting w/ A at the left (look closely and you'll find the letters).
5. If you post a copy of the page (or part of the page) you're talking about, I'd be able to help more.
07-19-2006, 12:18 PM
#3
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The large terminal (D+) is the alternator output, and should be hooked directly to the battery.
The small terminal is the excitor circuit. When the ignition switch is ON, power flows thru the charge light in the voltmeter on the instrument panel and the parallel-mounted resistor to this terminal. When the engine is running, the excitor current furnishes the power to start the magnetic field in the rotor, so that current can be generated in the stator. After the alternator starts generating power, it furnishes its own excitor current, and applies voltage to the excitor terminal. Since there is now voltage on both sides of the light, there is no current flow thru it, so it goes out.
X38 refers to Page X, Zone 38. If you look on Page X, in Zone 38, you will find the wire continuing at a box labeled I2, for Page I, Zone 2, which is where you started.
Since you don't say what your problem is, nor what model year you have, we can't tell you much more...
The small terminal is the excitor circuit. When the ignition switch is ON, power flows thru the charge light in the voltmeter on the instrument panel and the parallel-mounted resistor to this terminal. When the engine is running, the excitor current furnishes the power to start the magnetic field in the rotor, so that current can be generated in the stator. After the alternator starts generating power, it furnishes its own excitor current, and applies voltage to the excitor terminal. Since there is now voltage on both sides of the light, there is no current flow thru it, so it goes out.
X38 refers to Page X, Zone 38. If you look on Page X, in Zone 38, you will find the wire continuing at a box labeled I2, for Page I, Zone 2, which is where you started.
Since you don't say what your problem is, nor what model year you have, we can't tell you much more...
07-24-2006, 11:54 PM
#4
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That small post should be energized off +12V through a small 3W instrument bulb in parallel with a 68Ω 5W resistor. IIRC you should be seeing 9-10V there. You can wire up a spare bulb & resistor off the jump post & connect to the alternator terminal to verify alternator operation. The bulb and resistor both live in the instrument cluster.
