need you advise again. After long time I want to build something. I would like to avoid purchase of commercial vibrator controller, I would like to build it myself.
Controller has to have adjustable amplitude (electromagnet pull force) and frequency of vibration in order to achive/create resonance frequency with given bowl weight.
Electromagnet is ordinary AC transformer and its steel core is splitted, bigger part with coil winding and second just steel. Steel part is mounted on bottom of wi rator bowl. All this is no question. It is how it works (in short and simplified) and I do not need any advice in here.
But I need to control that electromagnet:)
Here is my initial concept:
PWM pin will be used to drive SSR relay. I know I have to use "proportional SSR" also called "Random on/off" instead of most most common "zero crossing off" relay in order to avoid long time response to on/off switching. Frequency range has to be of course higher than 30Hz, lets say up to 100Hz. Zero crossing off relay would not allow that.
I also did some reserch about electromagnets and DC seems to be more efficient and noiseless in compare to AC in case of electromagnets.
So idea is to use PWM to define amplitude e.g. pulling force and software timer to switch on/off that PWM pin in order to achieve desired frequency.
From loop cycle time should be not any issue to achieve 100Hz or even more.
High frequency PWM also should not produce any significant noise.
What do you think about it?
Also I am not sure about these:
if I should use bridge rectifier and DC SSR
if DC SSR can switch on/off at about 100Hz
or if better to use "random on/off AC SSR" for some particular reason
Any advice, experience or highlight point is welcomed and appreciated.
Thank you in advice for your time and support.
Hava a nice day all of you. Kind regards Mira
Paul's recommendation makes complete sense to me after some research. I want to build high power and high voltage H-bridge to test it and control vibration bowl prototype.
My current struggling point is circuit design. I am not electric engineer, so I would like to kindly ask someone who might have done similar circuit already for advice or direction.
Here is a bit background:
controller circuit has to be supplied by AC230V
after bridge rectifier and smoothing capacitor there will be about 320VDC
such a high voltage is not an issue for electromagnet coil, but of course I cannot let it run with 100% duty cycle, I will adjust max. duty cycle limit to match power rating of electromagnet
The issue is H-Bridge circuit which can withstand such a high voltage.
Is there anybody who have circuit idea for H-bridge capable of up to 320VDC and 2Amps?
In attachment is best circuit I could find. It use high voltage BJT transistors.
But I am not sure if it is good idea to test it with 320V, do you?
Other think I am not sure about the circuit is continuous current. Transistor power dissipation should be Rds(on) resistance multiplied by voltage based on ohms law. But how to calculate switching losses due to PWM switching frequency?
If one transistor heat dissipation is over rating, can I just wire two transistors in parallel?
I know I have too many questions. But any interest or advice is appreciated.
thank you in advance. Kind regards Mira
Forget all the electronic design stuff for right now and do a reality test.
Use a high power audio amplifier to drive your vibrator with ac from the amp. Feed the amp with an audio signal from a variable audio oscillator so you can discover the limits of frequency that your vibrator can handle. Document all very well, so you have something to base your future designs on. I can imagine the vibrations that are very far from your mains frequency will not be very great because of the transformer/solenoid/motor attached to the bowl.
Good luck with the project.
again, seems like brilliant suggestion.
Vibrator bowl is already existing and running, at this moment it is controlled by the commercial controller I borrowed. For that particular bowl I could achieve best performance (resonance frequency) with 67Hz. Electromagnet has DC resistance of 24 Ohms, and commercial controller feed about 0.6Amp. I learned that DC resistance cannot be used for current calculation because of induction and switching frequency.
But back to your suggestion. I can easily design electromagnet myself, means number of turns, wire gauge and so on. So I can get electromagnet with 8 Ohms coil and test with mono amplifier. If it works, I do not need to build my own circuit at all. I can stick with audio amplifier it self, but then other issue comes up.
ESP32 DAC output cannot provide frequency below 130Hz. But I suppose I can generate lower frequency with PWM and LC filter. What I do not understand in that scenario is how I can get push/pull from amplifier which is fed by given frequency. There will be negative voltage either?
I will try to measure some audio player output voltage with multimeter:)
I
Any audio amplifier worth anything will only create an AC signal. Two wires with the voltage alternating + and -, just like your mains power. If you feed an audio amplifier with a rectangular wave, the capacitors in the preamplifier circuit will immediately change that to AC for the rest of the amplifier to process. However the results will not be very nice to hear because of the rectangular wave. But your project doesn't care because you are not listening to it, but using it to power the vibrator.
