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Old 12-02-2002, 02:22 AM
Richard Wooldridge Richard Wooldridge is offline
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Join Date: Dec 2000
Location: Battle Ground, WA
Posts: 576
Hope I didn't offend!!

Hi there Medical Dave,
I hope I didn't come on too strong on my previous post, I suspected you just had a momentary lapse on the generator/alternator business, but wanted to make sure it was clarified for any other readers. I do think you are correct on the history of automotive alternators, however. One interesting thing is that a generator actually can be made capable of producing large charging currents at idle, but the engineers couldn't do that on automotive engines because if they made the pulley ratios such that the idle currents were high, the generators would "throw" the armature windings at higher engine speeds. For instance, my brother has a 1960's Ford Diesel tractor that will put out over 60 amps at idle, but it won't rev much higher than 2600 rpm, about half what the usual car engine will. Alternators have rotating fields, which are wound with much lighter wire and positive retaining designs, so they can spin a lot faster. This allows a smaller alternator pulley, contributing to the slipping belt problem. Those people that are goosing their engines to make the alternator start charging are just tightening the belts by centrifugal force to get the alternator up to speed...

Regards, Richard Wooldridge
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