03DelcoRemy Diagnostic Manual130004222020

delcoremy.com Page 3 NOTE The use of digital voltmeters is highly recommended for the following reasons: • Digital voltmeters are generally more accurate than analog (needle movement) instruments. • Digital readings need no interpretation; everyone sees the same number. • Digital instruments are generally auto ranging; they automatically select the proper range for the value of the reading. • Reversing polarity with a digital instrument will simply result in a negative reading (minus sign) whereas with an analog voltmeter, reversing polarity could damage the meter. • If analog meters are not read directly facing the meter, inaccuracies may result. 1-16. VOLTMETER USE. Figures 1-6 through 1-8 illustrate the proper use of the voltmeter and the types of readings that can be expected. 1. Figure 1-1 shows the voltmeter being used with no current flow or with the starter not operating. FIGURE 1-1. Voltmeter Readings with No Current Flow FIGURE 1-2. Voltmeter Readings with Current Flow NOTE When the voltmeter is connected parallel to a cable (meter leads and cable ends start and end at the same point), the meter will measure the voltage potential at both ends of the cable. Without current flowing, the values always will be the same and the voltmeter will read zero. 2. Figure 1-2 shows the voltmeter being used with current flow (starter pulling 500 amps). NOTE The V1 reading (See Figure 1-2) means that with 500 amps flowing through the positive cable, there is a 1.0 volt drop in that cable. There must be current flow in order to produce a voltage drop. The V2 reading (See Figure 1-2) of 0.3 volt means that with 500 amps flowing through the negative cable, there is a 0.3 volt drop in the negative cable. 3. Figure 1-3 illustrates the digital voltmeter reading in a DC system with both correct and incorrect polarity. Whenever the minus sign is displayed, the meter leads must be reversed to obtain the correct polarity. 0 V DP-1006 0 V O V V4 12.5V 0 V V3 0V 12.5 V 12.5V V2 12.5 V V1 0 V 0 V 12.5 V 12.5 V DP-1007 0.3 V 0.3 V V2 8.5 V V1 1.0 V 7.5 V 8.5 V V2 7.2 V 0.3 V V1 0 V 8.5 V 7.5 V