supplying accurate output voltage < input voltage

er than the voltage.

It's the motor itself that needs to be controlled. It gets too noisy at high speed. Laura

It's actually an industrial safety device. It's for use in environments that aren't immediately dangerous to life or health. Autobody workers use such respirators, because they work with chemicals like isocyanates that won't immediately cause damage, but you don't want to be breathing them long-term. If it fails on me I get sick for several days.

Laura

How close to maximum speed are you running the motor? If somewhere around 1/2 then there are pretty simple circuits that use feedback from the motor to regulate speed. I could email you a schematic of one. But a universal motor is a bad choice for this application. Cheap though. Another solution may be a CPAP machine. They are for forcing air down a snoring person's nasal passages to keep them breathing and stop the snoring. These devices are similar to your machine but have much better air pressure regulation and are quieter. I don't know if they put out as much air as you need because they are made for sleeping people but the one I have is adjustable to pretty high pressure and volume. They are available used for pretty cheap. Call a local Senior Center. The one I use is over 6 years old and still works great, especially considering it gets used every night. Eric

If it's a universal motor, it will run on DC, right?

So... How about using Zener diodes to regulate the voltage? Cheap and simple -- in theory.

Yes, you can inspect the brushes. Normally they should still have enough on them to have a good spring holding tension against the commutator.. Many of them put a mark on the side of the brush or crimp something on the lead wire to indicate when they should be changed.

Also, if you have gone through that many brushes already, it's a good chance the commutator is close to its life cycle. You need to inspect it for uneven surface wear which may include deep grooves.

Jamie

Much less than 1/2 max speed, I think. I measured the voltage the rheostat is outputting at my usual setting, and I was surprised to see it was 104 V, with ~ 120 V input. Ideally I'd have an inline sensor to measure air speed in the hose, and if the air speed is outside a preset range, the sensor would raise or lower the voltage.

An airline respirator has a powerful motor for pushing air through a long length of hose, unlike a CPAP machine.

Laura