FAQ
TL;DR: 280 W transformer rated to 30 kHz; "audio amps will not like 35–100 kHz at full power." Use a tuned transformer or dedicated driver to reach 50–150 V for piezos safely. [Elektroda, DAVID CUTHBERT, post #21661165]
Why it matters: This FAQ helps DIYers choose a workable, safe way to drive ultrasonic piezo transducers for cleaning without destroying an audio amp.
Quick Facts
- Target band: 35–100 kHz for cavitation cleaning with piezo transducers. [Elektroda, Tony Altobelli, post #21661157]
- Typical transducer draw: Approx. 40–75 W per element; high drive voltage often required. [Elektroda, Tony Altobelli, post #21661161]
- Sizing rule: About 100 W per gallon; a 40-gallon tank needs around 4 kW. [Elektroda, Tony Altobelli, post #21661162]
- Audio-amp caveat: Full-power operation at 35–100 kHz is unfavorable; derate or avoid. [Elektroda, DAVID CUTHBERT, post #21661165]
- Tuned-drive tip: Square wave into a transformer plus the piezo’s C forms a voltage-boosting LC; add series R to tame Q. [Elektroda, Todd Hayden, post #21661164]
Will a regular audio power amp drive a 35–100 kHz piezo transducer?
Not well at full power. Most audio amps roll off above ~20–30 kHz and can overheat or oscillate when loaded by piezo capacitance. As one contributor put it, "audio amps will not like running full bore at 35 kHz to 100 kHz." Use a purpose-built driver or transformer-coupled stage instead. [Elektroda, DAVID CUTHBERT, post #21661165]
How much power do typical ultrasonic cleaning transducers need?
Plan for approximately 40–75 W per transducer at resonance. Ultrasonic Langevin stacks often need high drive voltage to achieve the required acoustic power. Budget your driver and power supply with margin for mechanical loading and thermal limits. [Elektroda, Tony Altobelli, post #21661161]
How do I size power for my tank (rule of thumb)?
Use about 100 W per gallon of fluid. For example, a 40-gallon tank will need around 4,000 W total electrical input distributed across multiple transducers and drivers. Provide headroom for start-up and detuning under load. [Elektroda, Tony Altobelli, post #21661162]
What’s a practical driver topology to reach 50–150 V at 35–100 kHz?
Drive a power transformer with a square wave and let the transformer inductance and the piezo capacitance form a tuned LC. The LC filters the square wave into a near-sine and boosts voltage by the network’s Q. Add series resistance to control Q and protect the transducer. [Elektroda, Todd Hayden, post #21661164]
What does Q mean in this context?
Q (quality factor) quantifies resonance sharpness and energy storage versus loss. Higher Q increases voltage gain in your LC network but narrows bandwidth and raises risk of overvoltage. "Q factor" definitions cover bandwidth, energy, and damping relationships for resonant systems. [Q factor — Wikipedia]
Can I use an output transformer to match an audio amp to a piezo load?
Yes, with care. One approach proposed an 8 Ω to ~500 Ω match using a high-power output transformer. Example: Hammond 1650WA, 280 W, 1.9 kΩ to 4–8–16 Ω, with full-power bandwidth to 30 kHz; derate above that. Ensure thermal headroom and check stability. [Elektroda, DAVID CUTHBERT, post #21661165]
Is there a reference circuit for an ultrasonic cleaner driver?
Yes. See the RepairFAQ ultrasonic bath circuit referenced in the thread. It illustrates practical piezo drive methods and is a good starting point for scaling and experimenting before custom designs. Validate parts ratings for your target frequency and voltage. [Elektroda, Mark Harrington, post #21661163]
How do I characterize my Langevin transducer before building the driver?
Sweep frequency with a function generator and observe current/voltage to locate resonance. The OP notes building a Langevin and expecting resonant behavior; plan to verify with a scope once your test gear arrives. Record impedance versus frequency to guide matching. [Elektroda, Tony Altobelli, post #21661160]
How do I prevent overvoltage from a high‑Q tuned network?
Insert a known series resistor to reduce Q and limit voltage rise at resonance. This sacrifices some efficiency but improves stability and protects the piezo and transformer. It also broadens bandwidth for easier frequency tracking. [Elektroda, Todd Hayden, post #21661164]
Any specific transformer models or costs to expect?
One suggestion was the Hammond 1650WA output transformer, rated 280 W with full-power response to 30 kHz. A noted price example was about $323 via a major distributor. Confirm current pricing and consider derating above 30 kHz. [Elektroda, DAVID CUTHBERT, post #21661165]
Quick how-to: build a simple test driver for a piezo stack?
- Generate a square wave at the target frequency and feed a suitable power transformer.
- Let the transformer inductance and the piezo capacitance form a tuned LC at resonance.
- Add a series resistor to control Q; monitor voltage and temperature under load. [Elektroda, Todd Hayden, post #21661164]
Edge case: What happens if I drive 150 V into a 10 Ω load?
That implies 2.25 kW (V²/R), which is excessive and unsafe for small cleaners. Thermal and electrical limits will be exceeded. Re-evaluate the actual piezo impedance at resonance and design for realistic power levels. [Elektroda, Jeff Evemy, post #21661158]
Can I scale up the RepairFAQ bath circuit for higher power?
Yes, but validate transformer core size, switching devices, and heat dissipation. The OP planned to scale that approach; do staged tests and watch resonance peaks. Always verify with scope measurements before full-power operation. [Elektroda, Tony Altobelli, post #21661166]
Is 35–100 kHz a reasonable target for cavitation cleaning setups?
Yes. The project goal outlined this band for driving piezo transducers to create cavitation in deionized water. Ensure your driver, transformer, and transducers are characterized across this span and derate components appropriately. [Elektroda, Tony Altobelli, post #21661157]
