[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

Lucas and alternator problem

>Since I have diagnosed a massive short, and no charging from my 85
>4ksq's alternator, I have removed it. Now that it is off, I notice that
>the shaft turns without any resistance at all. From my limited
>experience with electric motors, I remember that I should feel a
>staggered resistance to turning. This problem seems odd to me. I have
>been told that the brushes and the diode pack can both go bad, but I do
>not know how this might affect the rotational resistance. Should I just
>take it apart and look for burnt-out wires and broken/worn pieces, or
>should I go out and buy a new one for way too much money? TIA!
>Dustin Sysko

Alternator shafts will turn with little or no resistance - the staggered
resistance you felt on electric motors was either residual magnetism or the
commutator (segmented).

Alternators have commutators, but actually, they are two concentric slip
rings, but since there are no joints or segments, you'll feel no changes in

Alternator repair: Mark case halves for alignment, disassemble. Check brush
length, spring tension (these are cheap - replace on sight).

Check rotor with ohmmeter or continuity tester: slip ring to slip ring
should show continuity, there should be no continuity to shaft from either
slip ring. Any other reading is bad (no continuity slip ring to slip ring
means field is open, continuity to shaft means field has a short - this
failure mode eats regulators).

Check armature (the part that DOESN'T turn in an alternator) for continuity
between wires, no shorts to ground. Note that there are two ways alternator
armatures are wired: Wye and delta. On Wye, an open segment will read zero,
but on delta, you must comapre the readings between all three wires 1-2,
2-3, 3-1, and they must be the same. Any pair that reads about half of the
other two pairs indicates an open segment. Correct resistance is on the
order of a few ohms.

    |                       /\
   / \  wye                /__\    delta

Diodes are checked as follows: Very low resistance one way, reverse
ohmmeter wires, very high resistance the other. Anything else = bad diode.

Clean parts, replace bearings and any parts checking bad, reassemble.
Alternator is fixed. One hour round trip for the first one you do, less

Now: Lucas. Lucas is NOT the Prince of Darkness. Lucas is the ****ing
INVENTOR of Darkness. I am utterly astonished that electrical equipment
with such a total, absolute intolerance for moisture comes from somewhere
that it rains most of the time. Back in the old days, I had a couple of
XK-120/140 Jaguars - if it rained within 100 miles the car wouldn't start.
If it got below 40 degrees, also no start. Then in 1969, I bought a BRAND
NEW Lotus Elan - in 15 years, Lucas hadn't learned an damn thing - exact
same problems! Except this car was in Miami, and would overheat instantly
if you went less than 50 mph.

Give me my Audi any day. (but I DO love the Sceptered Isle!)

Best Regards,

Mike Arman