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HMMWV 12 Volt Alternator Bracket Project Number 56C
January 2002
HMMWV
12 Volt
Alternator Bracket
National Association of State Foresters
in Cooperation with
Michigans Forest Fire Experiment Station 1
REC Project No. 56C
Making a 12 Volt Alternator Bracket
Table of Contents
Disclaimer...................................................................................................... 1
Introduction ................................................................................................... 2
Alternator Mounting Bracket Overview ......................................................... 2
Drive Pulley ................................................................................................... 3
Tensioning Bar .............................................................................................. 3
Aligning the Belt ............................................................................................ 4
Completing the Mounting Bracket Weldment ............................................... 4
Belt Sizing ..................................................................................................... 5
General.......................................................................................................... 5
Appendix A.................................................................................................... 6
Appendix B.................................................................................................... 8
Appendix C.................................................................................................. 10
Roscommon Equipment Center
c/o Forest Fire Experiment Station
1337 East Robinson Lake Road
P.O. Box 68
Roscommon, Michigan 48653
Telephone: (989) 275-5211
Fax: (989) 275-8249
Email: info@RoscommonEquipmentCenter.com
Web Site:
www.RoscommonEquipmentCenter.com
Disclaimer
This report has been developed for the guidance of member States, Provinces, Federal Agencies and
their cooperators. The National Association of State Foresters and the State of Michigan assume no
responsibility for the interpretation or use of this information.
The use of trade, firm or corporation names is for the information and convenience of the user. Such use
does not constitute an official evaluation, conclusion, recommendation, endorsement or approval of any
product or service to the exclusion of others, which may be suitable. 2
Introduction
A major decision for those converting a military vehicle to a fire truck concerns the electrical system. The
military vehicle will be 24 volt and most fire appliances require 12 volt. The HMMWVs are no exception.
Three choices are available:
§
Find radios, hose reel motors, emergency lights, and other add-ons in 24 volt and use the existing
system. Many items will be difficult to find in 24 volt.
§
Change the vehicles electric system to 12 volt, which requires considerable time, expense, and
expertise.
§
Add a separate 12 volt electric system, keeping the 24 volt one for the vehicle and using the 12 volt
for add-ons.
Project 56C guides you through the last choice by showing how to add an alternator. Appendix A
provides a schematic for wiring the system.
Alternator Mounting Bracket Overview
The military HMMWV has little room under the hood for mounting additional items. There is one spot
available in the right front corner of the engine compartment (passenger side) (Figure 1). This is normally
reserved on ambulance units for an air conditioner compressor. Most military vehicles will not have air
conditioning. If yours does, you will need to remove
it to accomplish this mounting.
A HMMWV air conditioner mounting bracket makes
a good starting point for making an alternator
bracket. Appendix B shows the part number for this
component (Item #13 on the drawing.). Its mounting
surfaces and holes were made to fit on the engine.
The pivot hole used to swivel the compressor for
belt tightening also works well as a pivot for
alternators. A pivot mounting tab was welded to the
bracket to help stiffen and secure the alternator. A
steel bar was also added to serve as the upper
mounting tab. Several models and photos illustrate
this. Figure 2 shows the five main parts of the
system. The air conditioner compressor bracket
(silver), upper mounting bracket (red), and pivot
mounting tab (blue), are welded to form a single
weldment. This will be described in more detail
later.
Figure 1 - The upper right side of the engine
compartment has an open area suitable for
mounting an alternator. Above is a 12 volt
alternator mounted to a modified HMMWV
compressor bracket. 3
Drive Pulley
Appendix C shows the fan pulley from the military HMMWV manual drawing. A fifth sheave (Item #21)
can be added to the normal four sheave pulley for driving the alternator. This is the sheave that drives
the compressor on air conditioner models.
Tensioning Bar
Make a tensioning bar from steel bar stock. There is not much swing clearance for alternator belt
tensioning in the space discussed, hence the bar does not need to be very long. A 3/8 inch wide by 4
inch long slot cut or milled into the center of a 1/4 inch x 1-1/4 inch x 5 inch long steel bar should be
adequate.
Figure 2 - Rear view model of RECs 12 volt alternator mounting for a HMMWV. The mounting consists
of five major parts, shown here. The upper mounting tab, tensioning bar, and pivot mounting tab must
be fabricated. 4
Aligning the Belt
Install the drive sheave and the unaltered compressor mounting bracket on the engine. Mount the
alternator temporarily to the front face of the compressor bracket pivot hole. Check to see if the drive
sheave and alternator pulley are aligned. With the Delco-Remy alternator used by REC, alignment was
very close. Achieve alignment by using washers or similar items as shims. Misalignment causes wear
that reduces belt life. Wildfire vehicles have relatively low use so some misalignment is tolerable as belt
life will be a relatively minor issue. However, aim for the best alignment possible.
Completing the Mounting Bracket Weldment
With the alternator aligned to the drive sheave, the mounting bracket can be completed. Bolt the
tensioning bar to the back of the alternators tensioning tab. Pivot the alternator midway in its available
swing range. Bend an approximate-shaped bar for
the upper mounting tab. This might take some trial
and error. Use a piece of poster board to estimate
and make a template. For the upper mounting tab:
§
Drill a mount hole (3/8 inch diameter) located
so that it mates with the tensioning bar in a
location that allows adequate adjustment.
§
Make sure the upper mounting tab will mate
with the compressor bracket to which it will be
welded.
§
The upper mounting tab must have at least 1
inch of overlap with the compressor bracket for
adequate weld attachment.
§
1/4 inch x 1-1/4 inch steel bar will make a
sturdy base for the piece.
§
Add gusset to stiffen the upper mount tab.
Make sure that the gusset overlaps the portion
welded to the compressor bracket.
Add the pivot mounting tab by bending a 1/4 inch x
1 inch steel bar as shown in Figure 3. This bar will
stiffen the alternator pivot, reducing vibration. A
stiffener may be required as shown welded to the
bottom of the bar.
Figure 3. The completed alternator mounting
bracket will look like this. The upper mounting tab
and pivot mounting tab are welded to a HMMWV
air conditioning compressor bracket. 5
Belt Sizing
After the alternator mount is welded on the bench,
reinstall it and the alternator. The length of the v-belt
can be determined using the following equation.
L = 2C + 1.57 (D + d) + (D - d)
2
/4C
Where L = Length of the v-belt.
C = The center-to-center distance
between the pulleys.
D = Diameter of largest pulley.
d = Diameter of smallest pulley.
It is not easy to measure the center-to-center
distance under the hood. Estimate the distance as
close as possible. Get belts a little smaller or larger
than the estimate so you can determine the best fit empirically. Install the shortest belt that will work so it
can be tightened when it stretches.
General
A specific design for the alternator system has been avoided, because exact dimensions will depend on
which alternator used. If modifying several vehicles, work out the details on one and from it make
templates. Welding fixtures can reduce the time needed to make the others. The cover photo and Figure
5 provide additional views of the assembly.
Figure 4 - Dimensions needed to estimate a
v-belt length.
Figure 5 - Front quartering view of the alternator
bracket. Alternator is shown semi-transparent. 6
U.S. Military vehicles operate with 24 volt DC
electrical systems. Fire departments converting
excess military vehicles to fire fighting equipment
generally need 12 volt DC to power many of their
accessories. REC Project #2, Wiring Conversion
on Military Vehicles, highlighted several ways to
provide 12 volt power. This Newsnote provides
an updated look at one of REC Projec