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Dead battery problems and a no start condition may result from your alternator not charging the battery. This is a very common car and truck concern. Most people will need a mechanic to sort this out, but there is one simple thing to try first.

Bonk the alternator with a hammer!

Why? (you ask!)

An alternator that has been around for some time, say one hundred thousand miles or more, can get sticking brushes. When the brushes stick in their holders, they may lose contact with the commutator rings. A sharp rap on the alternator case, (not hard enough to cause damage, but just enough to jar the parts), may get those brushes back in place.

If this intervention is successful, how can you tell? Well, if you have a voltmeter, have it reading system, (battery), voltage before you do the bonkin’. Engine running, but alternator not charging, voltage will probably be around 11.5v, maybe less if the battery is getting tired. When the alternator starts working this voltage should jump to 13+v to 14.7v, (depending on how depleted the battery is). You should also notice a distinct whining sound from the alternator as it works to charge the battery, possibly a drop in engine RPM and a brightening of the lights.

Interestingly, I just had this whole scenario play out on a 2001 Ford Escrort. I posted this article a few weeks ago, and on Tuesday, December 16th, 2008 I got a chance to review. The car came in with a not charging concern. I verified the condition, battery warning light on and system voltage, with the engine running was at about ten volts.  I then tapped the alternator and immediately the thing started charging. When I got the old unit out, I removed the regulator and brushes and one was worn down to where you could see the copper wire rubbed through the carbon. The contact ring on the armature had a corresponding groove cut into it. This examination proved that the procedure we are talking about is diagnostic and not a repair, though it might get you home.

Now for some more detail on the parts we are discussing. An alternator is a generator that produces alternating current, like household current. The alternating current is changed to DC (direct current) by passing it through a rectifier. Direct current is what the battery and the car’s electric system uses. The electricity is produced when wound wires are spun past a series of magnets. In order to get this electricity from the spinning rotor out to the car’s wires a method of contacting the spinning parts is used. This is done by the brushes I mentioned earlier. They are square carbon rods, about 3/16ths inch wide by an inch or so long. They sit, loosely, in square tubing holders that have springs in the end to push the brushes against the commutator. The brushes also have a wire each, that is connected to the rectifier and voltage regulator. Considering the environment they work in, these are amazingly reliable systems. Eventually, though, the brushes wear to the point that they can get sideways enough to stick in the holders. This is where the hammer comes in.  

This entry was posted on Saturday, November 29th, 2008 at 10:08 pm and is filed under chassis electrical. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.