Shel Hall writes:
>Several people have asked if I know of a specific Bosch substitution for
>the Lucas alternator in their Spitfires/Midgets/TR-?s/etc.
>
>The short answer is "No."
Good answer!!!!
>....
>Bosch alternators are also very popular with Hotrodders, because the
>single-wire output makes it easy to "sanitize" the engine compartment.
>Most of those guys are devoted to minimum under-hood clutter, and wiring
>harnesses and external voltage regulators epitomize under-hood clutter.
All self regulating alternators (what we're dealing with here) take a minimum
of three electrical paths to operate. Ground, usually through the frame. Field,
D+, a small wire normally driven by the idiot light on the dash. And, B+, hot,
Bat (etc.), connected directly to the battery hot side. *Most* Bosch
alternators use three wires with a frame ground. One field, and two hot's.
Most Lucas ACR's are the same way.
>As for mounting alternator X in place of alternator (or generator) Y,
>well, you may have to get creative. The typical Britcar generator mount
>(a piece of bent and punched sheet steel) could certainly be modified to
>accept the closer mounting points of an alternator, if a genuine
>alternator mount isn't available for that engine. If the new
>alternator's mount is narrower than the old one, you can add spacers.
>You just have to look and think. Just be sure the pulleys line up.
For most British cars, I recommend using a Lucas 17ACR. Mounting brackets,
wiring looms, etc. are available right off of the shelf.
>As for wiring, as far as I know the "hot" wire from the Bosch two-wire
>alternator goes straight to the positive side of the battery, and the
>ground wire goes straight to the _negative_ground_; on my BMW it just
>goes about 3" to the engine block.
Your BMW should just have a ground braid from the alternator frame to the
engine block. This is carry current past the brain-damaged, fan belt eating
rubber mounts BMW used on the alternator.
>In a negative-ground vehicle, the swap should be pretty
>straightforward, but on an older, positive-ground car you may have to do
>a little extra work. I don't know of any way to reverse the polarity on
>these alternators, and, although they are all-rubber-mounted, I don't
>think I'd depend on that to make a "hot chassis" isolated mounting work.
Nope, no easy way to reverse the polarity of an alternator. But, again,
they are not "all-rubber-mounted". Some other German manufacturers used
rubber mounts for the alternator brackets, but only BMW has the rubber
actually in the alternator frame.
> Much mo'bettah you should change the rest of the car to negative
>ground. Most of the positive-ground-era cars don't have much in the way
>of electronics; the lights don't care, the windshield wiper motor
>probably won't care, and the switches don't care. About all you'd have
>to change is the heater blower motor and the starter, and you may be
>able to modify those, I guess, or just trade them for similar units off
>a later, negative-ground car.
The starter won't care. The blower may or may not care. If it does care, it
will still work backwards, but not as well. Squirrel cage blows are
directional. The wiper motor does care. It will work backwards, but will
eat itself eventually. Old Lucas wiper motors have thrust bearings for
only one direction. Reversing it causes the worm gear to push the armature
towards the brushes, rather than the trust stop.
Randy
randy@taylor.UUCP
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