All in all, the EXISTING alternator MUST be POWERFUL (and be adjusted as explained
below) to be able to provide an adequate and stable power supply for the FWD/HWD Test
System.
Diode Unit and Alternator Voltage Adjustment
A so-called DIODE UNIT or Battery Separation Relay (provided if needed) should be
installed for battery separation if the existing alternator is used - see diagrams on a following
page. This Diode Unit or Battery Separation Relay serves two purposes:
First it is prevented that the electronics buffer battery voltage can drop at vehicle engine
starting and secondly the vehicle battery cannot be drained by the Test System.
If using the Diode Unit solution, the alternator output voltage should be adjusted (raised) to
approx. 15.0 Volts (instead of the normal 14.3 Volts) to compensate for the voltage drop of
the diodes in the Diode Unit. This alternator output voltage adjustment is often a problem as
most alternator regulators are NOT adjustable, but if the regulator is separated from the
alternator, it is possible to insert a diode in one of the three wires connecting the regulator to
the alternator, see diagrams on following pages. The diode should be inserted in the wire
denoted “D”, (or “+” or “IGN”), which is the most positive of the three wires (with the
alternator running).
NOTE that the magnetic field excitation current (a few Amps.) will flow through this diode,
so the diode used should have a current rating of at least 10A and if necessary be mounted
with a small heat sink to be able to withstand a continuous DC current of at least 5 Amps. The
diode should be a standard silicon diode, e.g. an “International Rectifier 21PT10” or similar,
which may be used without heat sink and be insulated with heat shrink tube.
Many modern alternators have the regulator mounted directly on the alternator housing with
no accessible connections, but in these cases it is normally possible to exchange such a
regulator with a field brushes holder, which can then be connected to a separate adjustable
regulator.
Heavy Fuse Box
A heavy fuse box (provided) with a 100A and a 25 (or 50)A fuse should be placed somewhere
between the Electronics Buffer Battery and the alternator, preferably closest to the battery.
The wiring to this fuse box depends on the alternator solution, so please refer to relevant
diagram(s).
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