I've been making a homemade fish scaler (the drum type) and I want to power it with a treadmill motor. It needs to run rather slow. I just have the dc motor and power cord, (has a red, black, and 2 blue wire from the motor). How can I get this to work? Can I use a rectifier and a dimmer switch? or do I need something else??
A dimmer and bridge rectifier won't handle it unless it is an awful large commercial dimmer. Most motors of that type use use an unfiltered SCR type controller for the PM motor. You likely want a 130 volt minimum 3 amp controller. That or some will work using a PWM drive. Unfortunately I don't have a drawing or schematic of either available. I would venture the red and black are power, especially if they are heavier than the blue wires. Possibly the blue are from a speed pickup but not sure.
Hopefully someone else will step in with a circuit or low cost solution.
Here's an eBay drive that may work for you: **broken link removed** Note, your treadmill motor may be rated 2 HP or so, but you may get by with a smaller controller, because you probably will not be pushing it that hard. The eBay controller is not 2HP. It is only about 1 HP.
For another source of drives, go to KB Electronics (https://www.kbelectronics.com/) and find out which of their drives will work for you. You need to match armature voltage and power. Most will be 110V single-phase input, but some are not.
Then check prices at Drives Warehouse (**broken link removed**). I have ordered several new drives from them and have not had any problems. If you decide to go used, I saw some on eBay for <$50. A search on "KB Drives" will get you there.
Not to rain on your parade, but why would you use a 6000 RPM motor if you want the drum to turn slowly? Even with a speed control the RPM of the motor when turned down will still be fairly fast. Using that high RPM motor will mean that you will need a speed reducer of some type in your scaler.
You know, you may have just stumbled on something. Spin the fish really, really fast and use a small air jet or electrical discharge (like in EDM) to blow the scales off it.