50DN Alternator Story

[Kurt Horvath]

Here you will find a complete history of the alternator most often used in heavy
applications for motor coaches. We hope that you find it helpful in providing
information on why your coach needs the properly remanufactured alternator and
not one of those lower costs ones that so may suppliers are offering.

We have "highlighted" specific points such as the special bearings mentioned as
critical. Their costs are substantially higher because they were manufactured
especially for this up-grade. Make sure to purchase only those alternators that
meet this DELCO specification.


The 50DN alternator has been the main electrical power supply for coaches since
its indtroduction in 1958. The requirements have increased from the original 12
volt, 215 amp to today's 24 volt, 270 amp output. Also, the mounting
configurations have proliferated to include several flange mountings and a
belt-driven version.

Remanufacturing units must be done for a specific application because the
possible combination of parts can create assemblies that would not function
properly on any OE vehicle and cause premature failure of the generator.
Servicing older units adds serveral other mountings and performances.

There have been several design modifications in various components in the 50-DN
alternator directed toward meeting the longer life desires of our customers.
SEVERAL of the changes can be incorporated in previously built units by the
fleet mechanics.

The rotor suppressor ring was changed from a brazed bronze ring to a TIG welded
STAINLESS STEEL ring. The strength of the assembly was greatly increased.

The stator conductor configuration was changed to increase the space between
conductors on both ends to reduce changes of shorting and the glass sleeving was
removed to obtain better cooling to increase stator life. Also the wire
insulation and impregnation were upgraded. Tests indicate the stator life has
been increased five fold.

The bearings and means to lubricate and cool them have been changed
significantly. An external oil line, tee and elbow were added as part of the
alternator assembly to deliver oil at the lowest practical temperature to the
bearings. The tee features a special small orifice in its upper leg to control
the amount of oil to the bearings. If a commercial tee is used, so much oil will
go to the bearings and too little oil will go to the alternator resulting in
higher alternator component temperature causing short generator life.

The double-row ball bearing was replaced by a SPECIAL roller bearing made to
NON-STANDARD dimensions. The radial clearance is less than a standard bearing to
reduce the chance of ROTOR RUB! Also, it was desirable to have the new roller
bearing fit into the same drive end housing bore as the double-row ball bearing,
so fleets could upgrade the alternators without the need to purchase a new
housing. However, the double-row ball bearing outer race is a slip fit in the
drive housing end bore and the roller bearing outer race MUST BE a press fit in
the housing. Therefore, the roller bearing outer diameter was made OVERSIZED. A
standard roller bearing WILL NOT FIT PROPERLY IN THE DRIVE END HOUSING BORE AND
MAY "WALK" TOWARD THE GEAR CREATING A SERIOUS PROBLEM AND OR PREMATURE ENGINE
FAILURE.

The single row ball bearing is special in that it has a SMALLER then normal
radial clearance, has heat treatment for high temperature operation, has a
shield on one side and the ball cage is made from reinforced nylon. The low
radial clearance is needed to prevent edge loading and the end of the rollers in
the roller bearing.. The shield needs to be placed next to the rotor to keep the
hotter oil in the generator away from the bearing and it also acts as a dam to
create a pool of oil in the bearing cavity.

Knowing who is remanufacturing your unit or providing you with an exchange and
knowing whether they know all the criteria as mentioned above, may mean the
difference of failure and optimum performance.


Kurt Horvath
95 PT 42
10AC