Iv had a triton powered respirator for years. The ni-cads gave out a long time ago and I thought I was being clever when I converted it to run off of an ac power supply. I only used in the shop when I was turning or when I emptied the dust collector so being tethered to an extension cord didn’t bother me. My power supply puts out 9v and 500ma. The fan runs ok but a bit slow. I’ve put up with that for, heck, 5 or 10 years.

then along comes Coronavirus and I’m dealing with my own short sightedness. If the thing was mobile, it would make the ultimate mask.

i found a guy on Etsy that is three-d printing power docks for various portable tool batteries. I have one for the Milwaukee m12 battery.

using a resistor substitution box, I found that about 5 ohms between the battery and the fan is about right.

so my thought is to put a 4 ohm resister in series with a 10 ohm potentiometer.

what I don’t know is the required wattage.

new battery power supply is 12v and 5 ohms seems to make it happy.

i know that an ac powered 9v .5a supply will run the thing but a bit slow.

i didnt want to run it very long as my resister substitution box is 1w.

Need a little ohms law coaching here.
9v x .5a = 4.5 watts, right?

should I be looking at 10w components?

be gentle, guys. I’m doing my best to remember stuff from a 1 semester electronics class in 1976.