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Yes and no Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 12 Apr 2007 06:23:58
In Reply to: charging problems, scania03, Wed, 11 Apr 2007 22:33:30 Members do not see ads below this line. - Help Keep This Site Online - Signup |
When does the light Not come on when the system isn't charging? When the light is causing the problem. That light is actually a critical part of the charging system.
Turn the key to ON, but don't start the car. Do you see the Battery light (this assumes the battery has enough charge left to at least get the dash lights on dim). If the light doesn't come on, it's time to troubleshoot.
An alternator is a generator, but instead of a permanent magnet, it uses an electromagnet (called the field coils). Therefore, the alternator need power to work. But it doesn't provide power until it's working !?! When you turn the key to ON, current flows from the battery, through the ignition key, through the BAT light, and through a thin wire to the D+ post on the back of the alternator, powering up the field coils. Since current flows through the bulb, it lights up. Once the engine starts and spins the alternator, it produces power on its own, and takes over powering the field coils. Since the alternator is providing current for the coils, none flows through the bulb, and it goes out. If the alternator stops working, current flows through the bulb and lights up.
BUT if the circuit through the bulb to the field coils is broken, the alternator never starts working. Not only doesn't the battery charge, it discharges because it's powering the car, not the alternator. And the BAT light is off. OK, not a great design, but one that's been around for half a century or so.
Visually check the alternator. Look for a thin yellow or green wire connected to the D+ post on the back of the alternator. (this is assuming the bulb didn't come on with the key in the ON position.) Make sure that wire is connected and in good condition. Make sure the alternator itself is properly grounded (a bad alternator ground will give the same symptoms). It is possible the bulb is bad, but highly unlikely. The bulb doesn't come on very often, so it's rare one burns out - a thin wire sitting in a hot engine compartment for 19 years is more likely to crack and break.
posted by 192.249....
, Thu, 12 Apr 2007 06:23:58 <-- Viewing This Message
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