Lenze 329171 AC7815 Dynamic Braking Resistor
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Product Information
The Lenze 329171 (Model AC7815) is a 15 Ohm dynamic braking resistor designed for use with Lenze AC Tech frequency inverters and variable speed drives. Functioning as a heavy-duty passive power component, this unit absorbs excess regenerative energy during rapid motor deceleration or under overhauling load conditions and dissipates it safely as heat. Featuring a rugged chassis and panel mount design, the module integrates directly into industrial control enclosures to support high-inertia stopping and high-cycle start-stop profiles across material handling, packaging machinery, textile manufacturing, and general factory automation.
Connecting the resistor to a drive is accomplished using power connection terminals or flying leads wired directly to the designated dynamic braking terminals, such as +/RB and -/RB or BR1 and BR2. Replacing a damaged braking resistor requires mechanical fastening onto the enclosure panel and secure connection to the inverter terminal strip. Because the unit is a hardware component without internal software or parameters, commissioning involves ensuring solid mechanical mounting for heat dissipation, inspecting lead integrity, and verifying that the drive parameters for dynamic braking functionality are enabled. ABC Industrial Parts supports maintenance teams with replacement units to quickly restore active deceleration capability in legacy drive systems.
Troubleshooting a suspected dynamic braking resistor involves isolating incoming power from the frequency inverter, allowing DC bus capacitors to discharge completely, and measuring electrical resistance across the resistor terminals using a digital ohmmeter. A functional unit reads approximately 15 Ohms across its connection terminals. An open circuit, infinite resistance reading, or visible thermal breakdown indicates internal resistor failure, which cannot be repaired on the board level and requires component replacement. Inspecting external wiring for loose terminal connections or heat degradation helps prevent drive overvoltage trips during heavy motor braking cycles.
Technical Specifications
| Manufacturer | Lenze |
| Part Number | 329171 |
| Model / Type | AC7815 |
| Component Type | Dynamic Braking Resistor |
| Product Family | AC Tech Accessories |
| Resistance | 15 Ohm |
| Mounting Type | Chassis / Panel Mount |
| Connection Type | Screw Terminals / Flying Leads |
Diagnostics and Status Indication
Diagnostic verification of the Lenze 329171 resistor relies on direct electrical testing rather than active electronic indicators. To test the unit, completely disconnect power from the drive system, verify safe capacitor discharge, and measure the electrical resistance across the resistor power terminals using a calibrated digital ohmmeter.
A measured value equal to the nominal 15 Ohms confirms functional continuity and element integrity. If the measurement reveals an infinite resistance value or significant drift, the internal resistive element has failed open, preventing the drive chopper circuit from dumping regenerative power and leading to drive overvoltage trips during motor deceleration.
Replacement and Spare Part Considerations
When replacing an existing Lenze 329171 AC7815 braking resistor, confirm that the replacement unit matches the nominal 15 Ohm resistance requirement. Installing a resistor with incorrect resistance can overload the drive internal braking transistor or fail to absorb sufficient energy, leading to nuisance overvoltage trips.
Ensure the mounting surface on the industrial control enclosure panel provides adequate thermal conductivity and clearance for heat dissipation into surrounding cabinet air. Attach all terminal leads firmly to the designated drive terminals (+/RB, -/RB, BR1, or BR2) before applying line power to the variable frequency drive.
Prior to placing a spare unit into operation, check all field wiring connections for thermal strain or oxidation. Confirm that the drive dynamic braking circuit parameters remain active so that regenerative energy is correctly routed to the 15 Ohm resistor during stopping cycles.
Frequently Asked Questions
How do I test if the Lenze 329171 dynamic braking resistor is working correctly?
Disconnect main power from the variable frequency drive, allow internal DC capacitors to discharge completely, and measure resistance across the resistor terminals with an ohmmeter. A healthy unit measures approximately 15 Ohms.
Which terminals on the drive connect to the Lenze AC7815 braking resistor?
The resistor wires directly to the dedicated dynamic braking terminals on compatible Lenze drives, typically marked as +/RB and -/RB or BR1 and BR2.
Does the Lenze 329171 resistor require software or parameter setup?
The resistor itself is a passive hardware component and requires no software or parameter transfer. However, the host drive must have its dynamic braking functions enabled within its parameter configuration.
What happens if a dynamic braking resistor fails open?
If the 15 Ohm resistor circuit opens, regenerative energy from decelerating motor loads cannot be dissipated, causing the variable frequency drive to trip on an overvoltage fault during deceleration.
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Disclaimer:
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