Designing a controller for ultrasonic cleaner - Page 1
Forum section: electronics / projects

author: Shay
author_rank: Regular Contributor
timestamp: January 06, 2024, 10:40:27 am
content: Hey,I'd like to make my own DIY ultrasonic cleaner. I've purchased from AliExpress 3 piezoelectric actuators:https://www.aliexpress.com/item/1005005266100309.html?spm=a2g0o.order_list.order_list_main.28.21ef1802tEBAqTAs far as I understand from one of the reviews, the impedance is about 5.3 ohms at about 40 kHz.Since the power is 60W at peak each, we can calculate that the voltage required at the resonance of those is about 17Vpeak and about 3.2Apeak. (is it peak power?)Assuming I'd like to utilize the maximum power and keep the voltage low enough, I'd need some kind of VCO that adjusts the frequency in order to maximize the power.I know the commercials use some kind of Royer converter, but it requires some custom parts that I'd like to avoid.I was thinking of some kind of PID controller integrated within a MCU and some current sensing with an ADC and sine wave output from a DAC that gets amplified. So the VCO and PID are done by the MCU.Is it possible? Is there any better soultion? And do those ultrasonics actually require such a low voltage?Thanks.

author: moffy
author_rank: Super Contributor
timestamp: January 06, 2024, 11:09:17 am
content: You could go the digital route and you would need to maximise power output by controlling the frequency, typically dithering the frequency to find and track the maximum power point. You wouldn't necessarily need a DAC, you could use PWM and a filter but the analogue route is simpler, if you are familiar with the analogue techniques.

author: Shay
author_rank: Regular Contributor
timestamp: January 06, 2024, 12:16:24 pm
content: Quote from: moffy on January 06, 2024, 11:09:17 amYes, that's why PID came into my mind.With an analogue route, something like an error amplifier that is controlling a VCO? the feedback is from the current, and the op amp adjusts the frequency in order to match the desired current.VCO -> Output AB stage -> Current Shunt -> Transducerfeedback from the current shunt into an OP amp. Reference current is generated in-phase by divding the output from the AB stage. Output of the op-amp into the VCO.Also, is the voltage I calculated is correct? I've seen on youtube that those powered by royer converter are fed with 1-2kV. Either they do this by keeping the transducer at generally high impedance since maybe it is easier to adjust the voltage than frequency. Not exacly sure?

author: inse
author_rank: Super Contributor
timestamp: January 06, 2024, 12:22:29 pm
content: How did you calculate the required voltage?Those piezo actuators are not ohmic loads, they are capacitive (a couple of nF)Usually those are driven with several hundreds of volts.For the Ali Express fan boys:https://de.aliexpress.com/item/1005005426026052.htmlThe core component is the driver transformer.Also you want to run this in resonance for efficiency.

author: Shay
author_rank: Regular Contributor
timestamp: January 06, 2024, 01:36:38 pm
content: This is where I thought I got it wrong.I assumed by the AliExpress review that the impedance at resonance is about 5.3 Ohm. So I simply used ohm law.If those are driven at high voltage, at 5.3 Ohm impedance at 40 kHz, the current would be huge, so I assumed they're driving it in a higher impedance.

author: moffy
author_rank: Super Contributor
timestamp: January 06, 2024, 02:13:10 pm
content: The resonance and impedance thing is interesting. The resonance is both electrical and mechanical and you want them both to align. The piezo transducers as inse stated look capacitive until they reach mechanical resonance and then they look resistive as well because they are doing work by substantial resonant motion. It is this motion you are trying to maximise. They do also require substantial voltages to drive the piezo electric element. You start with the transducer and its drive requirements then work backwards to the drive electronics. There is probably some mechanical design with regard to the transducer and what and how it attaches to help amplify the mechanical resonance rather than dampen it and if multiple elements are attached so that they interfere constructively rather than destructively.

author: inse
author_rank: Super Contributor
timestamp: January 06, 2024, 02:13:31 pm
content: Nothing to add to previous post

author: David Hess
author_rank: Super Contributor
timestamp: January 06, 2024, 03:17:14 pm
content: Quote from: Shay on January 06, 2024, 01:36:38 pmThe current is huge, but represents the circulating current between the transducer and external inductance at resonance. The driver only supplies power to make up for losses and the work done, but the voltage and current applied to the transducer and inductor are very large.

author: Shay
author_rank: Regular Contributor
timestamp: January 07, 2024, 09:16:42 pm
content: Quote from: moffy on January 06, 2024, 02:13:10 pmIf I understand correctly, it is not the lowest impedance I am trying to achieve, but rather a phase shift of 0 degrees between voltage and current - when the transducer are purely resistive.Quote from: David Hess on January 06, 2024, 03:17:14 pmSo kind of like an LC tank How can I know the voltages needed for the transducers?Where can I find information in regards to designing a driver specifically for ultrasonic cleaners?

author: inse
author_rank: Super Contributor
timestamp: January 07, 2024, 10:25:16 pm
content: As mentioned before: the core component is the transformer (pun not intended), would you design your own or try to source it?A driver board isn’t that expensive (see link above), but think of the other features of a commercial cleaner.You will need a suitable container, a lid, a heater + controller, a housing and a timer.I don’t know what is needed to reliably fix the transducers to the container.Apart from the learning factor it doesn’t make sense to develop your own from scratch (without design experience?).I bought a used one, it was broken, and fixed it.

author: moffy
author_rank: Super Contributor
timestamp: January 07, 2024, 11:15:19 pm
content: Quote from: Shay on January 07, 2024, 09:16:42 pmYou are looking for maximum power transfer, because there are reactive components it might not be exactly 0 degrees but it should be reasonably close.

author: David Hess
author_rank: Super Contributor
timestamp: January 08, 2024, 01:27:03 am
content: Quote from: inse on January 07, 2024, 10:25:16 pmI reverse engineered one that I really liked many years ago. It had a large ferrite rod inductor in series with the transducers for the resonance. The transformer was a trifilar wound pulse transformer which generated the drive for the transistors, but I do not remember how it was hooked up. None of my old ultrasonic cleaners use any sort of power transformer.

author: Shay
author_rank: Regular Contributor
timestamp: January 08, 2024, 06:07:54 pm
content: Quote from: inse on January 07, 2024, 10:25:16 pmI don't see anything practical about DIY too. I do it for the learning curve. As for the mechanical aspect, I have basically everything on hand. I don't think the Chinese use some kind of ultra-rare glue to fix the the Transducer. I'll experiment with it.

author: Shay
author_rank: Regular Contributor
timestamp: January 08, 2024, 06:09:20 pm
content: Quote from: moffy on January 07, 2024, 11:15:19 pmGot it. Thanks.