So to add a little more, first I had two 24V 1.05A fans. The PWM is 0-255 in range. At first I let them get to full speed when necessary and it worked for a while that way (it’s a night time air conditioner, basically). Then it started flaking out late morning where the thing would just lock up. I could see the last LCD update and knew every time this happened was at full bore and had suspicions.
So I dialed the max back to 235. And that seemed to help for a week or two, then it went back to dying late morning when it was at peak.
The power supply had plenty of 5V current, but was actually a 24V 2A supply. As you can see from above, at full speed I should have been drawing more like 2.1A, which is bad. But before I deployed this I had put a current meter on it and never saw more than about 1.8A total (either during acceleration to full speed nor while running at full speed).
But once this started happening at 235, I pulled it out and first thing I did was measure voltage at 235. It was dropping from 24V at under 100 to about 22.0V at 235, which means the current was likely climbing will above 2A. So I honestly think the 24V section was failing on that power supply.
So I ordered a new 5V/24V supply with a 4A 24V section. I installed it, but it was WORSE in that it was bouncing voltage all over the place when loaded or not.
So I’ve dropped back to a 5V/12V supply that does 3A on the 5V side with 12V 1.6A fans and strangely this setup works fine up to 255 with no issues whatsoever. Obviously I feel a little worried about this setup, too, but I plan to try yet another 24V supply for the 24V fans because they are a little higher output.
Anyway, just more to chew on.