DC Motor with speed control

Let me preface this by saying that I know very little practical stuff about hooking up motors. I'm a final year undergraduate EE student, and although I'm good with theory, working with actual motors is very different.

What I have is a Fasco 24V, 4.94A DC sealed ball bearing motor. Out the back are two wires, black and red, and then welded to the side is a small metal box with a variable control knob on its face. This box has a green wire coming from it. I know this motor is probably too small to worry about starting circuits. I have a DC power supply that was used previously to run this motor, but I have no knowledge of how it was hooked up and have no way to find out, either, which is unfortunate.

I have tried the following wiring combinations, in the order listed. I was careful to bring the voltage up from zero to 24V slowly, which I hoped would help avoid any burn-out in starting or blown fuses (don't know if this helps or not...).

• Red Wire -> Positive Terminal, Black Wire -> Negative Terminal, Green Wire -> float
• Red Wire -> Negative Terminal, Black Wire -> Positive Terminal, Green Wire -> float
• Red Wire -> Positive Terminal, Black Wire -> Negative Terminal, Green Wire -> Power Supply Chassis Ground
• Red Wire -> Positive Terminal, Black Wire -> Negative Terminal, Green Wire -> Negative Terminal
• Red Wire -> Positive Terminal, Black Wire -> Negative Terminal, Green Wire -> Positive Terminal

Under all of these conditions, the motor does not run and draws no current. I have checked the power supply, and it is working fine. The connection diagram on the motor's faceplate says only "red --- + supply, black --- - return". There is no mention of the knob and green wire, and the internet is surprisingly silent on my problem. If any of you have any insights, I would really, really appreciate it! Thanks very much for any input.

Looks like you have to look up the manufacturer's documentation to find out what this green wire means.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Green is often used to designate an earth ground connection, most often for safety (a UL or similar safety listing may require a ground connection in 24V systems) but also in certain circumstances to provide an attachment for EM shielding. When you examine the wire, where does it comes from? Does it happen to be internally attached to the motor chassis? (Continuity check will verify)

Thank you all for your help. I did a continuity check - the fuses were good, and it turns out the green wire is electrically connected to the motor chassis. I put in a call to Fasco, and the wires are supposed to be connected as Red->Positive, Black->Negative, Green->earth or chassis ground. I had already connected them up this way, so the rep suggested that the terminations are at fault. I cut off and re-terminated all of the wires with new connectors, and voila! I guess something must have happened with the old connectors. In any case, it works! Thanks again for the assistance