Resistive Amplifier Load-Bank Design
Definition: a controlled load whose electrical, thermal, mechanical, cooling, and protection behavior is known for the entire test interval.
Nameplate Watts Are Not The Assembled Rating
A resistor power rating normally depends on mounting, heatsink, airflow, ambient temperature, terminal temperature, and allowable element temperature. Adding printed watt ratings does not automatically produce a safe bank rating.
Electrical Design
- Calculate series and parallel resistance and branch current.
- Include resistor tolerance, wiring, terminals, fuses, switches, busbars and contacts.
- Measure assembled cold resistance and resistance at defined operating temperature.
- Use four-wire measurement where lead and connection resistance matter.
- Verify frequency dependence and inductance over the intended audio and class-D measurement bandwidth.
Thermal And Energy Design
| Limit | Question |
|---|---|
| continuous dissipation | What can the mounted and cooled assembly sustain? |
| pulse energy | What energy and peak power can the element absorb for the stated pulse? |
| temperature coefficient | How far does resistance move as the bank heats? |
| surface and internal temperature | Which point reaches its limit first? |
| recovery | What measured state must return before another run? |
Current Sharing
Parallel branches share current according to their complete hot resistance. Small differences in resistor value, lead length, lug resistance, or cooling can make one branch carry and dissipate more than intended. Measure branch current or branch voltage when validating a new bank.
Safety Architecture
- Guard all live and hot parts.
- Use temperature sensors at representative hotspots.
- Monitor fan or pump operation if cooling is active.
- Provide fusing, remote shutdown, strain relief and a noncombustible enclosure.
- Verify zero voltage and safe temperature before contact.
Required Record
Record component construction, values, tolerance, temperature coefficient, pulse data, mounting, cooling, wiring diagram, cold and hot resistance, inductance or frequency response, thermal sensors, duty cycle, shutdown limits, and measured recovery.