How alternator light works, a more detailed description |
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How alternator light works, a more detailed description |
Tom |
May 3 2014, 01:30 PM
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#1
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Advanced Member Group: Members Posts: 2,139 Joined: 21-August 05 From: Port Orchard, WA 98367 Member No.: 4,626 Region Association: None |
After reading many accounts of how this circuit works, I felt compelled to investigate further as I did not understand how two positives would cause a light to operate. They won't. One must be somewhat negative to complete the circuit. Internet searches turned up the same basic explanation, still was not buying it. I think it was being oversimplified.
This is how I think the alt light works: When the key is on and engine not running, there is 12 volts + at the alt light power side coming from the fused side of fuse #9. The other side goes to a junction on the relay board with D+. With the key to off and a meter connected between D+ and ground at the relay board, the reading is 12 ohms. As soon as the key is turned to on, the reading jumps to 12.5 meg ohms and the light comes on. If the wire for D+ to the alt is removed, the reading stays the same and the light stays on. Removing the VR caused the reading to jump to infinity and the light goes out. For the light to work, there has to be power to one side of the light and some resistance reading to ground for the other. Looking at the wiring diagram, one can follow the blue wire to the junction at the relay board at D+, then up thru the VR to a set of relay contacts, then down thru a ( resistor ?, not sure) and then down to the DF connection and on to the rotor where the current will produce a magnetic field. After the rotor, it goes to ground. When the alt spins enough RPM's, a voltage is produced and fed back to the VR, causing the relay to open and removes the ground path for the alt light. I could be entirely wrong here, but this is what I see and my readings more or less confirm it. If you see an error in my thinking, please post and let me know. Thanks, Tom Attached thumbnail(s) |
Spoke |
May 3 2014, 03:47 PM
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#2
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Jerry Group: Members Posts: 7,051 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
I could be entirely wrong here, but this is what I see and my readings more or less confirm it. If you see an error in my thinking, please post and let me know. Thanks, Tom Your findings are correct. The GEN light has 2 functions: 1) Indicate when the main charging path is not functioning correctly. There are 2 charging paths (see diagram). The one on the left powers the voltage regulator. The path on the right is the main path and powers the vehicle's electrical circuits and charges the battery. The GEN light is connected between these 2 paths. If the main path isn't providing enough voltage, there will be a difference of voltage across the GEN light and it will light up. 2) Provide the minute current necessary (when the engine is first started) to energize the magnet in the armature (the part of the alternator that turns). This is called bootstrapping since the alternator pulls its voltage up by its own generated voltage. #2 above is why if the GEN light is burned out or missing the alternator may fail to start up. It is possible for the alternator to start up since the armature magnet may have some residual magnetism when the engine is off. |
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