Schumacher PST-1000 Test Conclusions, Alternator Output Current Test Transformer Rectifier

3.Place the Amp Probe around the starter cable.

4.Connect the external volts positive lead to the positive terminal of the starter.

5.Connect the external volts negative lead to the starter ground.

6.Set the Volts Selector to External Volts ±199.9 volt range.

+ 24V

+

CRANKING

	BATTERY
	-	S	MAG
TR
			SW	STARTER

+ 12V

ALT

+

CHASSIS

BATTERY

-

12V LOADS

Figure 11

Transformer Rectifier Starter Draw Test

SWITCH

ALT

SERIES

PARALLEL

SWITCH

+

CHASSIS BATTERY

-

12V LOADS +

CRANKING

BATTERY

STARTER -

Figure 12

Series-Parallel Switch Starter Draw Test

Crank the engine for 15 seconds, and note the cranking amper- age reading. Also, watch to see that the starter voltage stays above 19.2 volts. Never crank the engine longer than 30 sec- onds. Wait at least two minutes for the starter to cool, if the test is to be repeated.

In some medium-duty applications, where there are two banks of CRANKING batteries, it may be necessary to connect the Amp Probe around both wires at once to read total current draw. If the wires are too far apart for the Amp Probe, simply measure the draw in each wire and add the results.

TEST CONCLUSIONS

The circuit is good if cranking speed was satisfactory and battery voltage at the starter stayed above 19.2 volts. Slow cranking speed is often caused by poor connections in the cranking circuit. Refer to the PST-1000 manual for troubleshooting information. In a 24 volt circuit, acceptable voltage drops are twice those for 12 volt circuits. If testing of the magnetic switch, solenoid, and other components reveal no problems, the starter should be replaced.

ALTERNATOR OUTPUT CURRENT TEST

TRANSFORMER RECTIFIER

There are two separate output wires. A 12 volt, high current out- put feeding the CHASSIS battery and a 24 volt, low current out- put, feeding the CRANKING battery. (See diagram below).

TEST PROCEDURE

12 Volt Output

1.Connect the Analyzer’s load cables across the CHASSIS battery.

2.Place the Amp Probe around the 12 volt output wire.

	+ 24V
	+
	CRANKING
	BATTERY
TR	-	S
		MAG

	SW	STARTER
ALT	+ 12V
	+
	CHASSIS
	BATTERY
	-
	12V LOADS

Figure 13

Transformer-Rectifier Alternator Output Test-12V

3.Set the Volts Selector to Battery Volts.

4.Run the engine at about 2000 RPM.

5.Turn the Load ON and increase until the battery voltage is between 12.5 and 13.5 volts while reading the output amperage.

6.Turn the Load OFF and reduce RPM.

TEST CONCLUSIONS

1.If the Diode/Stator lamp stayed on during the output test, replace the alternator.

2.If the amperage abruptly decreased during the test, check for a loose belt.

3.If output was less than 90% of rating, see PST-1000 manual for output resistance test procedures.

	+ 24V
	+
	CRANKING
	BATTERY
TR	-	S	MAG
			SW	STARTER
ALT	+ 12V
	+
	CHASSIS
	BATTERY
	-

12V LOADS

Figure 14

Transformer-Rectifier Alternator Output Test-24V

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