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Diode issues Posted by Ari [Email] ![]() ![]() In Reply to: Re: Battery Light, John Roberts, Wed, 7 Sep 2005 08:55:20 Members do not see ads below this line. - Help Keep This Site Online - Signup |
With a bad diode, the output of the alternator is low. The alternator produces alternating (AC) current - the car uses DC. There are diodes in there to rectify the AC into DC. If one of the diodes is blown, voltage from that coil won't flow, and the output voltage is (on average) lower. When the alternator output is a lower voltage than the battery, the battery light comes on.
In all my years of playing with cars, I've only had one blown alternator diode, but I've had bunches of worn out Voltage Regulators. So just going on averages, change the VR. Much cheaper and easier. The other clue is that sometimes the voltage is OK. Sometimes worn brushes make good enough contact, and you get a decent voltage and the battery light goes out. It is possible that there is an intermittent diode, but most likely it will be blown, and the light will not go out on occasion.
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