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| Place of Origin | Germany |
| Brand Name | SIEMENS |
| Certification | CE ROHS |
| Model Number | 6RY1703-0EA01 C98043-A7004-L1 |
Part Number: C98043-A7004-L1
Alternate Reference: 6RY1703-0EA01
Manufacturer: Siemens AG (Germany)
Product Type: Field Supply Board (FSB) — DC Motor Excitation Control
The C98043-A7004-L1 is the Field Supply Board for the Siemens SIMOREG DC-MASTER 6RA70 series DC drive converters. In a separately-excited DC motor — the type used in high-performance variable-speed drive applications — the field winding establishes the magnetic flux in the motor's stator.
The armature winding interacts with this flux to produce torque. Controlling the field current is therefore controlling one of the two fundamental variables of DC motor operation.
The C98043-A7004-L1 is the board that manages this field current. It contains the thyristor bridge and control circuits for the field converter section of the 6RA70 drive, converting the single-phase AC field supply voltage into a precisely controlled DC output for the motor's field winding.
he board implements both the field current control loop — maintaining field current at the setpoint — and the field weakening control that allows the motor to run above its base speed by reducing field current as speed increases.
Field weakening is what gives DC drives their extended speed range. Below base speed, the field is maintained at rated current and torque is controlled by varying armature current.
Above base speed, the field is weakened — current is reduced — allowing higher speed at reduced maximum torque. The C98043-A7004-L1 executes this field control over the full speed range.
| Parameter | Value |
|---|---|
| Part Number | C98043-A7004-L1 |
| Alternate Order No. | 6RY1703-0EA01 |
| Manufacturer | Siemens AG |
| Product Type | Field Supply Board (FSB) |
| Product Family | SIMOREG DC-MASTER 6RA70 |
| Function | Controlled DC excitation for motor field winding |
| Control | Field current regulation, field weakening, field loss protection |
| Country of Origin | Germany |
The magnetic field in a separately-excited DC motor is not permanent — it is created by passing DC current through the field winding. The strength of this field directly affects the motor's performance characteristics.
At full field, the motor develops maximum torque at rated armature current. This is the preferred condition for low-speed, high-torque operation — rolling mills, extruders, and heavy-process drives running at or below base speed depend on full field strength.
As speed increases above base speed, the armature voltage would exceed the drive's maximum output if field were maintained constant. Instead, the C98043-A7004-L1 reduces field current in a controlled manner — field weakening — allowing the motor to run faster at the cost of reduced maximum torque.
The torque-speed envelope above base speed follows a constant-power characteristic: double the speed, half the available torque.
This capability is critical for applications requiring wide speed ranges: winders must run at variable speed to maintain constant surface speed as roll diameter changes; test stands need continuous speed variation across a wide range; process lines run at different speeds for different products.
One of the most important safety functions on the C98043-A7004-L1 is field loss detection. If the field current falls below a defined threshold — due to a field supply failure, a field winding open circuit, or a board fault — the motor loses its magnetic flux.
Under this condition, the motor cannot develop controlled torque from its armature current. In extreme cases, an unfluxed motor connected to a high-voltage armature supply may accelerate uncontrollably.
The C98043-A7004-L1 monitors field current continuously.
A confirmed field loss detection causes an immediate drive trip, isolating the armature supply before a dangerous overspeed condition can develop.
This protective function operates independently of the main control software and represents a hardware safety layer for the overall drive system.
Within the C98043-A7004 Field Supply Board series, the L-suffix identifies the board variant and revision. The L1 designation covers the standard field supply board configuration suitable for the majority of SIMOREG 6RA70 single-quadrant and four-quadrant converter applications.
Later variants (L2 and beyond) addressed specific application requirements or incorporated field improvements.
For most standard 6RA70 applications, the C98043-A7004-L1 is the applicable field supply board.
Confirm the variant against the drive's original hardware configuration or the label on the installed board before sourcing a replacement.
The field winding of a separately-excited DC motor is a high-inductance coil. This inductance has important implications for field supply design. When field current changes — whether during speed-up, speed-down, or field weakening transitions — the inductance opposes the change.
The C98043-A7004-L1's control loop must account for this inductance to achieve stable, responsive field current control.
Field circuit time constants for large DC motors can be in the range of seconds. The board's control loop is tuned for the motor's field inductance and resistance, typically set during commissioning.
If the C98043-A7004-L1 is replaced, verify that the field regulator parameters (stored in the CUD1) are appropriate for the motor — incorrect field regulator tuning can produce field current instability, slow field buildup at start, or oscillatory field weakening response.
Q1: The 6RA70 drive shows F036 (field controller setpoint/actual value deviation too large). Is the C98043-A7004-L1 the likely fault source?
F036 indicates that the field current is significantly below the commanded setpoint. Before concluding the FSB has failed, check the field supply AC input voltage at the board's supply terminals and verify the motor's field winding resistance with the motor disconnected (to rule out an open-circuit or high-resistance field winding).
A blown field fuse is also a common cause.
If supply voltage and field winding resistance are confirmed normal, the C98043-A7004-L1 thyristor bridge or its control circuit may have failed and board replacement is required.
Q2: After installing a replacement C98043-A7004-L1, the drive shows oscillatory field current at base speed. What should be adjusted?
Oscillatory field current typically indicates that the field regulator gain or time constant parameters in the CUD1 are not matched to the motor's field inductance and resistance. This is a parameter issue, not a board fault.
Access the field regulator parameters in the CUD1's commissioning screens and verify they match the motor's field circuit characteristics.
If the original parameter set was not documented, a field regulator auto-tune (if available in the firmware version) or manual tuning based on the motor's nameplate field data is required.
Q3: The L1 version is in stock but the drive previously had an L2 version. Is L1 backward compatible?
In the C98043-A7004 series, L-variant compatibility depends on the specific 6RA70 converter configuration. For standard applications within the 6RA70 power range, the L1 and L2 differ in specific circuit characteristics matched to different field supply voltage ranges or current ratings.
Confirm the required field supply voltage (from the drive's type plate or the installed board's label) matches the L1 version's specification before installation.
Installing a mismatched variant can result in incorrect field current levels.
Q4: The motor is running at twice base speed using field weakening. If the C98043-A7004-L1 fails in this condition, what happens?
A field supply failure during field weakening causes an immediate drive trip via the field loss detection circuit on the board — assuming the field loss detection is functioning correctly. The armature is disconnected. With a working field loss detection, the motor decelerates safely.
If the field loss detection circuit itself has failed and does not trip the drive, field current collapses while armature voltage is maintained.
In this scenario, the motor may accelerate to dangerous speeds. This is why the field loss protection function should be periodically tested as part of scheduled drive maintenance.
Q5: The 6RA70 drive is being retrofitted with a SINAMICS DCM to replace the aging SIMOREG hardware. Does the C98043-A7004-L1 have any equivalent in the SINAMICS DCM architecture?
The SINAMICS DCM handles field excitation internally — the field thyristor bridge and control are integrated within the DCM hardware architecture.
There is no separate field supply board to specify when ordering a SINAMICS DCM, as this function is built in. When migrating from 6RA70 to SINAMICS DCM, the field current control parameters (field current setpoints, field weakening characteristic) are re-entered as SINAMICS DCM parameters during commissioning.
The old 6RA70 parameter documentation serves as reference but requires translation to SINAMICS parameter numbering.
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