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Electrical: Engine Starting, Charging
case, located at the grounding point for the brush set, rectifier bridge and in some
cases, the regulator. Where are they mounted? On the rear case half, and how is
the rear case half attached to the front? Typically with four through bolts
sandwiching the field between them. Most alternators use the front case half as the
mount for the belt adjusters and block attachment. With the engine running, it is
always a good idea to measure a voltage drop between the front and rear case
halves to ensure great connections.
Testing Alternator/Battery Voltage and Amps.
Battery Load Test:
[Motor Magazine, Apr 2002] A load test indicates how well a battery can deliver
current while still maintaining enough voltage to operate the ignition system. This
is generally the preferred test for any battery in a late-model vehicle. A battery
must be at least one-half to three-quarters charged for an accurate load test-
preferably fully charged. A load test places a specific current load on the battery to
indicate how it will perform under heavier demands, such as cranking. A good
battery should deliver the specified current while maintaining a voltage of 9.6 volts
or more for 15 seconds at 70 F. As noted earlier, a cold battery delivers less
current than a warm one, so the minimum voltage specs must be compensated for
temperature. At 30 F, minimum voltage drops to 9.1 volts; at 0 F, it's 8.5 volts. If
you have a digital voltmeter with Min/Max recording capability, you can do a fast
load test that yields quite reliable results. First, connect your voltmeter across the
battery and select the Min/Max recording function. Now turn on the headlights and
crank the engine until it starts. Finally, let the engine run for about 10 seconds,
then shut it down. The minimum recorded voltage on your meter is the lowest
voltage reached by the battery during cranking. The maximum recorded reading is
the alternator recovery voltage after the engine started.
Charging Amps:
With the engine idling and no load on the charging system (lights and all
accessories off, battery fully charged), the amperage output should be relatively
low (typically less than 10 amps). With the headlights and heater blower fan on
and the engine running at 2,000 rpm, the output should jump to a higher reading,
typically 25-30 amps or more. Charging voltage varies according to underhood
temperatures. Room temperature charging voltage is generally about 14.2 volts. As
underhood temperatures increase, charging voltage drops down to about 13.8
volts. In very cold climates, charging voltage may temporarily increase to 14.8 or
perhaps 15.0 volts.
Voltage Drop in Cables:
Test
the voltage drop in the battery cables to ensure that corrosion or internal
failures are not preventing a charge. [Tip: Jim Bowers] There should be less that
0.2 volt drop from the alternator to the battery + terminal. My car had a bad crimp
on the lug at the alternator and after I bought it I had no-starts due to a depleted
battery. After starting the engine while the battery was recharging, I measured 0.5
volts from the alternator stud to the wire just after the lug. I cleaned and soldered
the crimp lug and while I was at it also replaced the regulator/brush assembly. I've
file:///C|/Users/Steve/Documents/Volvo%20FAQ%20Updated/ElectricalStarting.html[01/13/14 10:02:47 PM]
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