Fan Speed Control

2112 wrote:

What happens when battery power is too low to move the fan and the PWM is sending out power still? Harm to fan? Harm to controller?

That could be a problem. A quality controller would use a low voltage dropout regulator to protect itself from this. The one you pointed to can regulate down to 10 volts. It could heat up below that. You will have some line loss depending on what wire you use. A battery voltage below 11.5V (just my guess) might create 10V at the controller.

Why not try the one you pointed to on eBay? It's $13 delivered. 25KHz switching frequency so it shouldn't be noisy, rated for 10A and has a power switch. I assume you already have the wires located where you want it on the wall. Did you run 16awg wire? Wires being too small/long could be a problem.

The eBay link one is the closest to what I have, same plastic case (no vent holes), so it will fit right in.
I will have to go investigate what wire. Most of the wire run is big wire, and I do not own any smaller than 18g, but if it is 18 then it is just a small section... However, running fan on a low output speed my guess is 18g wire is not coming into play here.

What Im worried is that I forgot and left the fan on overnight, on a low speed, just fast enough to keep running, and maybe the batteries, 7 yrs old now, got a little lower over night and the fan stopped running, but was getting power sent to it, and sent through the controller still.
I know from audio that when this sort of thing happens to a speaker you can melt the voice coils, low-power can hurt a speaker more than too much. (weak signal to a two-way speaker and the smaller speaker takes all the power, not the big speaker... I wont get into details).
So, I am not sure if it was my fault and I melted something with a non-running fan, or it the controller just died naturally. I dont want to blame the vax if it was truly a natural death sort of thing...