Cheapest and easiest way to slow down a motor

[BrianBSL]

Originally Posted by sanddrag

I need to electrically slow down the motor. Sorry I wasn't clear on that. I only have a 12VDC supply. The motor will probably pull something like 4 amps continuous its application. It will be running continuously for maybe 5 hours. Wouldn't the resistor get very hot and need lots of cooling?

Not much more so than any lightbulb thats going to give you the voltage drop you want.

Originally Posted by sanddrag

I have two or three of these motors I'll be using in the system. I'm wondering if I could get what I want by just wiring them all in series.

Don't see any reason why not, as long as you arn't hoping for perfectly equal speeds. Just be careful about chassis grounded stuff if they are from automotive applications. (Don't think you usually have to worry about this with motors, but just an FYI)

Originally Posted by sanddrag

Also, would anyone happen to know what is inside this box? Thanks.

I'm guessing a rheostat, but thats purely a guess, assuming its designed for DC. It (the harbor freight link) is a little unclear about if its for DC or AC. A rheostat is going to throw as much heat as a resistor in the same application.

Basically, if you want to do the same voltage drop, and draw the same current, you have to do something with the power you are throwing away across that voltage drop, likely to heat.

I'd just see if I can find some power resistors. If you get one big enough (over-rated enough on power) then you wouldn't have to worry about any type of forced air cooling.