PWM to constant DC voltage for fan control

Egon.Net

@dc42 said in PWM to constant DC voltage for fan control:

@egon-net did you include the resistance of the inductor in your simulation? It's 2.1 ohms for the inductor that @bananapuppy is thinking of using. If the capacitor is electrolytic then you should include its ESR in the simulation too.

What happens if you simulate using a lower value capacitor, or no capacitor at all?

I added a 2 Ohm series resistor to the inductor, but didn't add anything to the capacitor (I'm used to use low ESR electrolytics). I'll perform a test and show the results.
Regarding the capacitor, the lower the capacitor the smaller the transient, but the worse the ripple too.

Egon.Net

@dc42 here are the results:

2.1 Ohm ESR for Inductor, 7 Ohm ESR for capacitor, 100%PWM:

It still overshoots, but less than before.

Now, witha 100nF capacitor, 50% PWM:

The overshoot is almost gone, but ripple increases.

And finally without capacitor at all (same 50% PWM):

No transient, but lots of ripple.

dc42

@egon-net thanks, looks like 100nF might be a good value to use then.

bananapuppy

@egon-net thanks for making these graphs, very useful to me! Does the voltage still overshoot to about 16V with 100% PWM, when using a 100nF capacitor?

How about a capacitor somewhere between 100nF and 1µF? I.e. 0.47µF for instance, I figure that might be a nice middle ground for ripple with not too much of an overshoot ?

Egon.Net

@bananapuppy you are welcome
With a 100nF capacitor the overshoot should be about 1.5V (13.5V max for 12V), and ripple about 1Vpp

The bigger the cap, the bigger the overshoot.

dc42

A ripple of 1V p-p is unlikely to matter.

Egon.Net

@dc42 said in PWM to constant DC voltage for fan control:

A ripple of 1V p-p is unlikely to matter.

I agree.

Is there any drawback for the Duet with the highest PWM frequencies (CPU/resource usage wise) besides a tiny bit more power consumed by the mosfet?

bananapuppy

@egon-net @dc42 thanks! I recon the following should do for a capacitor then? A ceramic one, as electrolytic doesn't even seem available at 100nF, does that matter? There was mention of ESR with use of an electrolytic capacitor / being used in the simulation?

SA105E104MARTB AVX

Egon.Net

@bananapuppy said in PWM to constant DC voltage for fan control:

SA105E104MARTB AVX

Ceramic is ok, but I'd try to get one with X5R or X7R dielectric. The one you picked has Z5U dielectric which is not that good.

bananapuppy

@egon-net no idea what that difference means (if someone can recommend me a good electronics course, please do ), but the following should be good then!?

CM-100N-X7R SR PASSIVES

dc42

@bananapuppy said in PWM to constant DC voltage for fan control:

CM-100N-X7R

Yes, that's 100nF 100V X7R.

dc42

@egon-net said in PWM to constant DC voltage for fan control:

@dc42 said in PWM to constant DC voltage for fan control:

A ripple of 1V p-p is unlikely to matter.

I agree.

Is there any drawback for the Duet with the highest PWM frequencies (CPU/resource usage wise) besides a tiny bit more power consumed by the mosfet?

Just a little more heat dissipation in the mosfet, and perhaps slightly poorer resolution in the PWM setting.

Egon.Net

@dc42 nice, thanks!