Foo - How would the DC motor behave?

I have an application for a DC motor, already got the motor and its the perfect size. Its about 200W, got the right amount of torque I need.
The problem is the RPM is too high. The motor comes with a controller which feeds it 110VDC. THe motor draws 1.8amps, and the controller shuts down automatically when the motor tries to pull probably 2 or more amps. This motor will go at a max of 4000RPM, well beyond what I need it for. So heres a question;
What if I was to feed this motor say, 30v, but the power supply was capable of 15Amps output. Also the controller is good for 10amps. Since not so much voltage is being forced through the motor, the motor would spin more slowly. But would it try to make up for the lack of voltage by drawing more amps? So it would keep the same torque?
Also, would it lower the RPM that hte motor has practicly no torque?

RPM is a function of voltage and torque is a function of amps. They're both related and you can't change one without affecting the other. If you lower the voltage to lower RPMs, then the amps and torque goes down as well. The very bottom line is the windings of a certain diameter wire with a certain number of windings. If you want different characteristics, you gotta change the windings.

Due to hysteresis and free-rev speed, lowest amp-draw occurs there. The higher the load, which lowers the RPM, the higher current-draw will be. Is it really drawing 1.8amps with no load?

Another way to slow down the motor is through gearing. You'll have the benefits of higher-torque and lower amperage-draw.


+1

I was going to answer this having grown up in a business that worked with a lot of DC motors, but MOthra is correct. I would agree...try using a gear or serpentine belted pulley to reduce the rpms at the point of contact(i.e. what you are ultimately trying to turn) with two gears (or pulleys) you can effectively find the rpm range you want for the application. But everything Mothra wrote is 100% accurate. Good job Mothra!

We completely f**ked up a 1/3rd AC motor and 40:1 gear box by running the motor at 500F (wiring melted, shorted) and running the gear box upside down (oil leaked) plus running it in a cyclical application. Those motors need continuous operation for the internal fan to work, due to thermal and fluid inertia and such.

Now we've got a DC motor and we're rewiring a new controls system for it. The best way to dramatically change it w/o damage to the motor is get a gear box. And for the love of god, when the label starts melting off the motor, turn it off!

We got our box from boston gear through mickey carr. They offered to send us a new one for free if we send the old one back.

+1

I was going to answer this having grown up in a business that worked with a lot of DC motors, but MOthra is correct. I would agree...try using a gear or serpentine belted pulley to reduce the rpms at the point of contact(i.e. what you are ultimately trying to turn) with two gears (or pulleys) you can effectively find the rpm range you want for the application. But everything Mothra wrote is 100% accurate. Good job Mothra!

I should steal the "Relax, it's all good" quote from your signature and put it in mine...

I should steal the "Relax, it's all good" quote from your signature and put it in mine...
But that would require effort, and taking off the gloves.

The answer has already been posted, so instead I'll add my only semi-related story to this.

We all know how starter motors for cars work - high RPM for low periods of time. Also know that there is some pretty heavy oil/grease in it. Now when you take that high RPM motor, put a load on it to slow it down and run it for about 5minutes... you get some pretty darn thin liquid running out.

I guess I will gear it down, :(. Was trying to avoid that, but alright. Ideally a 10:1 gearbox would be nice. Probably not worth me buying one, as lovely as McMaster is. I will see if I can make something.