Smoothed fan PWM wiring

Diamondback

Hello,

I've already seen a few posts about using low-pass filters for converting fan PWM outputs to a smooth-ish DC voltage, but I've got a few more specific questions.

Here's some info on my components:

24V supply
24V / 0.5A / 12W radial blowers (yes, they are big fans)
Duet 2 + Duex5

I want to use 2 of those fans for a static part cooling system in my Toolchanger. Since these are not PWM fans and they work really well when just controlled by voltage (start to turn around 6V@0.1A), I was thinking about smoothing the PWM signal and have a better time driving the fans.

I was reading in another post by @dc42 that a low-pass filter with an indcutor gives the best results in this scenario and was wondering which specific components I should choose.
My main concern is the rather large power draw of the fans (almost 30W overall), so I need some help spec'ing the components correctly.

I plan on connecting the fans in parallel to one of the heater outputs of the Duex, is that alright?

Can someone help me?

Diamondback

Anyone? Maybe @dc42 ?

fcwilt

@diamondback

I cannot help you with this sort of thing.

There was a member who was selling "smoothing" devices. Perhaps you can find his posts.

Frederick

cosmowave

@diamondback @fcwilt it was @zapta

oliof

@PCR did build some too

dc42

@diamondback you will need an inductor with inductance of at least 1mH and with both rated current and saturation current at least 1A. Perhaps this one https://www.digikey.co.uk/en/products/detail/bourns-inc/2124-V-RC/775402. Also a 10uF capacitor rated at 35V or more.

You will need to use either a fan output on the Duet (not the DueX, because you can't select a high PWM frequency on the DueX), or a heater output. If you use a heater output then you will also need an external flyback diode. If you use a fan output then unless your Duet is quite old, it will be included on the Duet.

Diamondback

@dc42 Thaks a lot David, I ordered the components. Also good tip about the flyback, did not have that on my mind...

Diamondback

@dc42 I've wired everything up and it's working very well! Thanks again!
One question though, What effect does the PWM frequency have? Is a specific value needed other than "as high as possible"?

PCR

@diamondback about 65khz i think

PCR

@diamondback
65535

dc42

@diamondback said in Smoothed fan PWM wiring:

@dc42 I've wired everything up and it's working very well! Thanks again!
One question though, What effect does the PWM frequency have? Is a specific value needed other than "as high as possible"?

The smoothing is only effective at high PWM frequencies (you would need a larger inductor for it to work at lower frequencies). The maximum PWM frequency supported is 65535 Hz.