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Motor noise reduction
I run tc4+ heat gun flour sifter combo. My heat gun board had one 25V 470uf electrolytic and cbb22 105j400V film capacitor. Motor itself like most 18V, but optimal work load between 12-25. I run motor separately from tc4+ for better temperature readings at the moment with separate pwm regulator and 25V 5A psu. I soldered flyback diode 1N4004 and 1000uf electrolytic cap directly to motor. I twisted leads and placed ferrite pair of rings (toroidal; L: 6.3mm; Ĝint: 10.1mm; Ĝout: 16.5mm; 72nH; 200kHz HF-065125) with 1 twist to motor end and another pair (toroidal; L: 4.83mm; Ĝint: 7.7mm; Ĝout: 12.7mm; 4.9nH; T50-2) with 1 twist to psu end. Wire is 1mm3 ~30cm motor to pwm regulator, 1mm3 ~15cm pwm regulator to psu.
Question: I received 470uf electrolytic and variety of ceramic caps:
A) Should I modify or run the setup as is (psu is still working)?
B) Thinking of 3 ceramic caps ( 2 in series and 1 parallel). Don't know which caps to choose.
C) Does ferrite ring must be exact for setup (wire lenght and mm3) or something is better than nothing.
D) Should I remove electrolytic cap when ceramic in place; replace 1000uf to 470uf.
What noise ? Acoustic or EMI ?

A brushless motor could be a possible answer for both.
Those used in RC hobby, for example, are quite cheap.

This change is actually mandatory sooner or later, the motors used in popcorn machines have a life under 10 hours.
This is more than the standard one year warranty, when used as popcorn roasters, i.e. 1 minute cycle, lower than 180 C degrees, so these machines usually last enough years to not hear complaints.
But when moded for 10 minutes cycles, over 200C, they fail quickly, maybe even 100 roasts.
The above are valid for the typical 385 class Mabuchi/Johnson low voltage DC motors, used in most EU popcorn roasters.
The US roasters are using much beefy mains voltage A/C motors, with longer life.
Edited by renatoa on 05/20/2022 10:56 AM
I was thinking about EMI noise. I will investigate about brushless motors for future upgrade. It would be good for lacking emi noise and longetivity. I haven't had brushless experience for 12 years when I built diy gimbal and drone.
But still I am interested about cancelling out EMI noise on my current brushed motor. Can someone with a popper tell which ceramic capacitors were used?
Instead of electrolytic, I placed 3 103 ceramic caps. I guess it worked for emi cancelling, but the motor definately needed starting cap and to even out ripple. RPM dropped more than half. So 470uf 25V made it fly again. I did notice a bosch replacement dc fan for heat gun having 3 turns of wire through a single ferrite toroid for both.
Yep, most poppers I moded have two coils in the filtering setup, one on each motor line.
And three ceramic capacitors, one bigger, parallel with motor poles, and two smaller, from each motor pole to the case.
No values noted, unfortunately.

A schematic attached, ignore values.

The bigger electrolytic capacitor don't make sense for me, DC motors don't need start capacitors.
Could be rather related to weak power source, unable to provide peak currents when brushes are switching.
renatoa attached the following image:
PSU is cheap 24v 5A switching one. Well electrolytic cap didn't blow with 20 roasts and was cool to touch after roast.
Probably low ESR, if no warm.
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