Friday, September 17, 2010

Journey of discovery

Today, I am going to take you with me as I go on a journey of discovery, troubleshooting an alternator problem. There is some risk in this, blogwise, since I don't know in advance what the outcome will be. We'll be shooting for a fully working alternator...

To set things up for you:
The Problem
The alternator does not start making electricity when the engine is started. Sometimes several minutes elapse before output appears. It seems that momentarily racing the engine will sometimes get it going.

Background: Alternators, How They Work
To make electricity, you spin a coil in a magnetic field (a generator) or spin a magnetic field in a coil (an alternator). Now where does that magnetic field come from? In both devices, it is made by passing an electric current thru another coil (it's an electromagnet). So, until you supply electricity to the field coil, you just have one coil spinning inside another coil... it's pretty, but it doesn't make electricity. Once the alternator is making electricity, some of that output is redirected internally to the field coil, so it becomes self sufficient.

This bootstrap problem is solved by supplying a little electricity from the battery to the alternator field coil. In a car, that current passes thru a small lite on the dash labeled 'Alt'... when the lite is lit, the alternator is not making electricity. Once it is delivering electricity and its own field excitation current, power stops flowing from the battery thru the lite, and the lite goes out.

What's happening on Eolian?
No output means no field current. Delayed output means delayed field current. There is one more possibility, that I think is likely: If there is a residual, small magnetic field in the iron core of the field coil, it could be enough to kickstart things if you spin the alternator fast enough. That is, I suspect that what we'll find is that there is NO field excitation current being delivered to the alternator, due to a bad connection or a broken wire.

Next post: Stay with me today as the journey begins...

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