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Discussion Starter #1 (Edited)
Hi,
some BMWs have their alternators disabled/suspended during acceleration and that helps both the go and the consumption. AFAIK, the alternators have two sets of windings - one on the rotor and one on the stator. One of these (I guess the one on the rotor) must receive a bias (magnetic filed generating) current that is varied so that the alternator output voltage is around 14 V regardless of RPM. There is also a relay (I assume) than only connects the alternator to the electric network of the car and the battery when that voltage is OK. So, how about making an electromechanical device to cut off the bias current of the alternator during acceleration? I am imagining a small pipe, curved up - the back end points somewhat upwards, with 2 holes on the sides (in the horizontal bottom part) for a LED and a photo transistor, and a steel ball traveling in the pipe. The current through the photo-transistor (when the car accelerates) will open a normally-closed relay to cut the bias current. Such a simple setup would produce abrupt cut-offs and restarts of the bias current. Would that work? Anyone with knowledge of alternators?
EDIT: A switch like the one on the handbrake, hooked up on the throttle, would be simpler. The question still is: would I burn components with the abrupt changes in the bias current?
Cheers,
Borislav
 

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Good electronic science there... Nev? Too expensive to fit on moderately priced machines though? And I guess summat' else to go wrong? Highly technical, Borislav, but interesting nevertheless. Hi! and welcome.:):
 

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Once the engine exceeds 3000rpm or so, a traditional alternator's field windings self-excite and it will charge. You will not be able to engineer in a switch for a traditional alternator, and only a newer switchable type, which is bespoke to the engine will work and fit. Perhaps even a regulator with programmable or variable voltage may work. I don't know if such a thing exists, but it may be possible under the desired conditions to use a different regulator set to a lower charge voltage. You then still need some type of a switch. A switch on the throttle should be the easiest soution, unless the ECU has an extra output controlled by sensing WOT (wide open throttle).

A lot of effort for minimal gains. A remap would be a better solution.
I applaud your thinking though.:thumbs:
 
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