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The Power Train Electric Drive System will contain hazardous voltage levels during machine operation and for a short period of time after engine shutdown. Do not remove any covers that will expose energized high voltage electrical components while the engine is operating. Any type of maintenance on the following components can only be performed after the Power Train Electrical System Service Shutdown procedure has been followed:
Failure to follow these instructions could result in personal injury or death. |
The "Crowbar Thyristor Test" can be activated using the Cat® Electronic Technician (Cat® ET). The test can be used as an aide in troubleshooting the driver circuits for the "Crowbar" and for testing the operation of the "Crowbar" thyristor.
This test can be performed anytime that the operation of the "Crowbar" and the associated circuits needs to be verified.
Activation of any of the following "Motor 1 ECM" events could possibly be caused by faulty operation of the "Crowbar" or a related circuit.
- E0757 - Crowbar Not Responding to Command
- E0911 - Unexpected Chopper Module Output Current Detected
When a machine area that contains high-voltage components must be entered, the "Power Train Electrical System Service Shutdown" procedure must be performed. The procedure must be performed before the cover for the compartment is removed.
Reference: Refer to Troubleshooting, UENR3890, "Cat 794 AC Off-Highway Truck/Tractor" and perform the "Power Train Electrical System Service Shutdown" procedure. Verify that the voltage in the drive train system has been discharged. Once the voltage of the DC bus in the"Inverter Retarding Contactor" compartment has been verified as discharged, and a jumper wire is in place, return to this point in this procedure and continue.
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| Illustration 1 | g03674774 |
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View of the rear of the inverter cabinet Crowbar circuit connections (1) Crowbar assembly harness connector (2) Thyristor anode positive (+) side bus bar connection to the CHN cable (3) Thyristor cathode negative (-) side bus bar connection to the DCN cable | |
The "Crowbar" is a solid-state thyristor which is also referred to as a silicon-controlled rectifier (SCR). When the thyristor is OFF (open), no current will flow through the device. When turned ON (closed), the thyristor will conduct current in only one direction.
In the electric drivetrain system, the "Crowbar" is used as an over voltage control device. When the "Crowbar" is activated, the positive (+) DC Power Bus is shorted to the negative (-) DC Power Bus through the "Retarding Grid 1" resistor elements.
Either the "Motor Control 1 ECM" or the "Motor Control 2 ECM" can command Interface "Module 2" to activate the "Crowbar". To activate the "Crowbar", an ECM will send a voltage pulse to "Interface Module 2". "Interface Module 2" will convert the voltage pulse to a single light pulse in a fiber optic driver circuit that is connected to the crowbar assembly. The optical pulse is converted back to a voltage pulse in the electronic crowbar gate driver circuit.
An interface module fiber optic driver circuit is connected to the crowbar assembly. The fiber optic circuit provides isolation between the low voltage control circuits and the high-voltage circuits that are connected to the "Crowbar".
When the "Crowbar" is turned ON, the thyristor will remain in the latched ON (closed) state. The battery disconnect switch must be turned OFF to unlatch (open) the thyristor.
The thyristor has an anode (A) connection to one side of the "Retarding Grid 1" resistor elements. The other side of the resistor elements is connected to the positive "(+) DC Power Bus". A cathode connection is connected to the negative (-) DC Power Bus.
When the gate of the thyristor is biased by the voltage pulse, the electrical current from the positive (+) DC bus is directed through the "Retarding Grid 1" resistor elements and on to the negative (-) DC bus through the conducting thyristor. The result is an immediate discharge of the "DC Power Bus" voltage.
The following test will enable the user to activate the sinking driver circuit. The contractor coils will be energized which will close the contractors. The contractors can remain in the CLOSED state to check the control circuit, the feedback circuit, and the pilot relay for the correct operation.
- Verify that the "Electrical Shutdown and Voltage Discharge" procedure has been performed and that the right rear cover is removed from the Inverter cabinet contractor compartment.
- At the thyristor bus bar connections in the rear of the compartment, disconnect the CHN cable positive (+) cable from the bus bar.
- Turn the "Battery Disconnect Switch" to the ON position. Turn the "Engine Lockout Control" to the ON (lock out) position. The low voltage control system will be energized at the +battery level regardless of the state of the key start switch.
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Illustration 2 g06356213 Selection of the "Crowbar Protection Circuit Test" in Cat® ET - Connect and start Cat® ET. When the "Available ECM(s)" screen appears, select the "Motor Control #1 ECM".
- In the main screen for the "Motor Control 1 ECM", select "Diagnostics" from the menu bar. From the pull-down menu, select "Diagnostic Tests", then select "Crowbar Protection Circuit Test".
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Illustration 3 g06356217 "Crowbar Protection Circuit Test" in Cat® ET - Follow the instructions presented on the screen to satisfy the preconditions for the test. As the conditions are satisfied, each condition will be grayed out. The ECM will not allow the test to proceed until all preconditions are satisfied.
- Once the preconditions and the setup conditions are satisfied, the user is given the option of turning ON the ECM driver circuit for the Crowbar or turning OFF the ECM driver circuit for the "Crowbar".
- When the instruction states: "To turn ON the overvoltage control rectifier, click the Next> button”, clicking the NEXT button on the bottom left-hand side of the screen will activate (close) the crowbar thyristor. When the instruction states: To turn OFF the overvoltage control rectifier, click the NEXT button, clicking the NEXT button on the bottom left-hand side of the screen will deactivate (OPEN) the crowbar thyristor.
Note: When the "Crowbar" is commanded to close, the Cat® ET screen will not provide an indication that the "Crowbar" is activated or closed. This operation will be checked in the following steps. After the test is completed, the "Successfully Completed" message only indicates that the test is done. The message does not indicate that the circuits or the "Crowbar" have operated properly.
Note: Watching the moving text will inform the operator of the current step. If the text is not moving, the test is not being run.
- At the bus bars in the front of the "Crowbar" compartment, use a multimeter to check the resistance across the thyristor. Place the positive probe on the positive (+) bus bar. Place the negative probe on the negative (-) bus bar.
- Observe the resistance measurement. The resistance should be high or infinite (OL).
- Close the "Crowbar" thyristor. The resistance should change to a lower resistance value.
- Open the "Crowbar" thyristor. The resistance should change to a high or infinite (OL) resistance value.
- Reverse the multimeter probes. Place the positive probe on the negative (-) bus bar. Place the negative probe on the positive (+) bus bar.
- With the "Crowbar" thyristor OPEN, observe the resistance measurement. The resistance should be high or infinite (OL) resistance value.
- CLOSE the "Crowbar" thyristor. The resistance should remain at a high or infinite (OL) resistance value.
Expected Result:
The resistance measurements are indicating that the operation of the "Crowbar" thyristor is correct.
Results:
OK - The operation of the "Crowbar" thyristor and the control circuits is correct.
The test is completed. The "Crowbar" is operating properly.
STOP.
NOT OK - The resistance measurements did not register as expected when the thyristor is cycled ON and OFF. There is a problem in the control circuit or with the crowbar assembly.
Proceed to the next "Troubleshooting the Crowbar Circuits" section to check the operation of the control circuits.
The following troubleshooting steps will help to determine if there is a problem in the control circuits or a problem with the thyristor.
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| Illustration 4 | g02135033 |
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Typical view (4) Crowbar thyristor (5) 24 VAC power supply circuits (6) Ground circuit (7) Optical driver circuit | |
The fiber optic circuits and connectors require special handling to ensure proper operation. Mishandling of the circuits or connectors can result in either poor circuit operation or a complete failure of the circuit.
The fiber optic circuits and the fiber optic connectors are not serviceable.
If a fiber optic harness circuit or a fiber optic harness connector is damaged or has failed, the complete harness for the involved phase module will have to be replaced.
If a fiber optic connector on the interface module or the crowbar assembly is damaged, the interface module or the crowbar assembly will have to be replaced.
Refer to the Testing and Adjusting, "Fiber Optic Connector Handling" for the proper disconnection and connection procedures.
- Open the Crowbar thyristor in the diagnostic assembly, carefully disconnect the control circuit harness connector.
Note: Ensure that the 24 VAC have been removed before disconnecting any connector.
- At the harness connector, use a multimeter to check the voltage between the 24 VAC contact F (wire AC24OVA) and the 24 VAC contact G (wire AC24OVB). The voltage should be approximately 24 VAC.
- Use a multimeter to check the resistance (continuity) between the ground contact G (wire GND9) and a good cabinet ground point. The resistance should be less than 5.0 ohms.
- While closely observing the fiber optic driver circuit (contact A) on the harness connector, close the "Crowbar" thyristor. A red light should be observed on the fiber optic contact.
Expected Result:
The power supply voltage and ground circuits are present at the harness connector for the "Crowbar" assembly. The fiber optic red light signal is present at the optical contact when the driver circuit is ON.
Results:
OK - All the control circuits are present as expected at the harness connector for the crowbar assembly.
Repair:
If all the circuits have been checked at the harness connector and a problem has not been found, the indication is that the "Crowbar" thyristor or the integrated electronic circuits on the assembly are not working.
Replace the crowbar assembly.
After replacing the crowbar assembly, perform this test again to ensure that the problem has been resolved.
STOP.
NOT OK - Either the power or the ground circuits did not check as expected or the fiber optic driver circuit did not perform as expected.
Repair:
If a 24 VAC power circuit is not correct, refer to the connection diagram at the beginning of this procedure. Check the voltage at the circuits on the 70-pin control connector for "Interface Module 2".
If the voltage is not present at the interface module contacts when the "Crowbar" test is active and the "Crowbar" is CLOSED, the interface module may be causing the problem. Mark the "Interface Module 2" and switch the module with the "Interface Module 1". This switch can be done without flashing any software.
If the "Interface Module 1" performs correctly when connected as "Interface Module 2", replace the marked interface module.
If the fiber optic driver circuit did not perform as expected when the "Crowbar" is CLOSED, go to the "Interface Module 2" and disconnect the single fiber optic driver circuit (OOV1) connector. Use Cat® ET to CLOSE the "Crowbar". The red light should be observed at the connector on the interface module.
If the light signal is not present at the interface module connector, use "spoon" probes to check for an ECM driver voltage at the "Interface Module 2" control connector contact 19 (wire GOVD2). A voltage of between 5.0 VDC and 15.0 VDC should be present when the crowbar is commanded to close.
If the driver voltage is not observed, check for the voltage at the "Motor Control 1 ECM" contact J2-39 (wire GOVD2) with the "Crowbar" commanded to be closed.
If the driver voltage is not observed, check for the voltage at the "Motor Control 1 ECM" contact J2-39 (wire GOVD2) with the "Crowbar" commanded to be closed.
Use Cat® ET to close the "Crowbar". If the voltage is not observed at the "Motor Control 1 ECM" connector, the ECM could possibly be causing the problem.
Turn OFF the battery disconnect switch. Switch the "Motor Control 1 ECM" and the "Motor Control 2 ECM" to determine if the ECM is causing the problem. Refer to any of the troubleshooting procedures for diagnostic codes possibly activated by either Motor Control ECM for a procedure on how to switch each ECM.
If the indication is that the ECM is causing the problem, replace the faulty ECM. After replacing the ECM, perform this test again to ensure that the problem has been resolved.