The 90A to 110A Alternator Upgrade

[DeWitt Harrison <de@aztek-eng.com>]

The following is the culmination of a long running
struggle with my charging system. This may not be
the full answer either but things are working well
for the  time being.

Type 44 Charging System Problems - The 90A to 110A
Alternator Upgrade

Background:

As the full size Audi sedan evolved over time -
from the early eighties 5000 to the early nineties
200 20V - there was a steady escalation in the
demand placed upon the electrical system. The
increased demand has arisen from additional electrical
equipment such as ABS, enhanced A/C, fuel pumping
capacity, and higher cooling fan loads due to engine
output increases. The addition of turbocharging
resulted in a quantum leap in cooling requirements.
Performance modifications of various kinds can
place further demands on the electrical generating
capacity of the system.

There has been a corresponding factory upgrading of
the alternator rating from 55A to 65A to 90A to 110A.
For reasons which, just to keep life interesting,
I prefer to leave open to debate, some Type 44
vehicles equipped with 90A alternators experience
a shortfall of charging capacity under certain
circumstances. The typical circumstance is operation
in stop-and-go traffic, or repeated stops with
restarts - as in running errands around town -
during HOT summer weather. Enhanced cooling
modifications such as fan blade changes, thermostat
temperature rating changes, daytime electrical
load changes such as high output sound systems
and the like can exacerbate these problems. In
contrast, cold weather charging problems tend to
be associated with battery aging problems or with
wiring deficiencies such as corroded ground bonding
strap connections.

Charging capacity shortfall can be difficult to
diagnose. Often the charging system will check out
satisfactorily under load testing at the repair
shop or Audi dealer. An additional variable, which 
is endemic to the type 44, is the notoriously
unreliable in-line splice in the alternator-to-battery
cable run. This large butt splice connection, located
on the passenger side of the firewall, frequently
experiences a resistance increase sufficient to
seriously impair the electrical system. The battery-to-
body, frame-to-engine block and the alternator-to-
firewall cable connections should also be viewed
with great suspicion. The battery must be healthy
and the cooling system should be in top shape.

I am now of the opinion that the 90A charging system
is subject to collapse due to a thermal runaway
condition.  Since the resistance of copper wire
increases with temperature, the efficiency of the
alternator will decrease as it becomes hotter. As
the efficiency decreases and the output voltage
falls, the voltage regulator will compensate by
placing a higher demand on the alternator. The
demand increase will result in increased heat
dissipation within the alternator with a corresponding
decrease in efficiency. The resulting positive feedback
syndrome will cause the alternator output voltage to
fall below useful charging levels, say 12.5V. In
my case, in hot weather, I have frequently experienced
situations were the electrical needs of the car could only
be satisfied by battery discharge while running!
The 110A upgrade seems to have eliminated this
shortfall.

Upgrade:

If all attempts to remedy a charging system shortfall
have been in vain, consider upgrading the alternator
capacity to 110A. My personal theory is that the 90A
alternator was a very marginal rating for the MC
engined cars. In such a situation, any small change,
be it an unwitting alteration in the electrical load
or a slight system impairment due to aging or wear,
could push the 90A unit over the edge. Audi made this
change for its own reasons sometime during the 1989
or 1990 200TQ model run. Many MC equipped cars from
that period and all 3B engines are fitted with the
110A unit. Do you suppose this was on a whim?

You will need to purchase

  1. One Bosch AL179X rebuilt alternator
       (without core exchange)
  2. One 034 903 143 B alternator mounting bracket
       (buy used if possible)
  3. Two N 100 520 01 alternator mounting bolts
       (M10x48 shoulder self-locking bolts)
  4. One 034 903 171 alternator cooling fan wheel
  5. One 034 903 119 G alternator pulley
  6. Four M5-0.8x10mm bolts (cooling cover)

The alternator cooling inlet cover and duct-work, the
9.5x825mm or 10x825mm V-belt, rubber bump stopper
from the stock mounting bracket, the pulley nut
and washers, all the adjusting hardware and support
braces and all the original alternator bracket-
to-block mounting hardware may be reused.
All electrical connections are unchanged. If you buy
the alternator bracket used - watch that the used
price does not exceed the new price - chances are
that it will come with the necessary M10 shoulder
bolts and bump stop.

With the exception of the mounting bracket and
the cooling cover attachment hardware (bolts are
needed in place of the hex nuts), everything
may be reused during the conversion, at least temporarily.
(The 90A fan wheel blades will hit the alternator face
so the fan washer must be moved to the rear of the
fan wheel as a spacer.) **However**, due to a 5-6 mm
forward offset of the 110A alternator pulley shaft
reference location, the V-belt will be badly mis-aligned
unless the fan wheel and pulley are also changed as suggested.
Don't run this way for long.

A few tips:

Loosen all the mounting fasteners and all the brace strut
hardware enough so that the alternator can pivot without
force. This will prevent the stripping of the tension adjustment
cog bolt. Also re-tighten all these same fasteners. The bolt
at the top of the tension adjustment arm is easy to overlook
but will cause a oil leak that looks like a bad front main seal.
Avoid scaring yourself. Take the time to find them all.
Tool-wise, you will need a 8 mm hex drive and a 24 mm
wrench to deal with the pulley nut. Bentley says 25 ft-lbs.
That's not all that easy to loosen. I kept waiting for the
8mm driver to explode. Be prepared for a bit of a battle.
I didn't give quite the full 25 ft-lbs on reinstall. Finally,
although not necessary, I prefer to take the 2 minutes to
remove the front bumper cover. It really improves access.

Happy charging.

DeWitt Harrison
Boulder, CO
88 5kcstq