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Dc motor performance

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jwmay

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#1
So I traded a 1/4 hp ac motor for a 1.5 hp dc treadmill motor. The treadmill motor is rated for 4800 rpm, which seemed too high to be useful, but I was planning to use it with a Focus1 dc controller, and hoped I could slow it down and still get torque. Most dc motors I’ve worked with have been very strong. Dayton’s, pacific Scientific, and Baldor are what I’m used to seeing and working on. And I understand that these are all high dollar motors. Anyhow that wasn’t the case. It’s exceptionally weak at any speed. Although I admit I didn’t run it at 4800. But still, a hp is a hp. I’m hoping for a technical answer here.

So I hooked up an 1/8hp Dayton motor to this same controller last night, and that little booger was unstoppable at any speed. So what gives? Why is this treadmill motor so weak?

And how do you who use them, find suitable motors to use? Are there certain models of treadmill you look for? This one came from a Weslo. The part number of the motor is 118180.
 

Ulma Doctor

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#2
the controller seems to be the issue, if i had to guess.
my theory is that the controller doesn't supply the amps/watts necessary to run the 1.5hp motor effectively.
if you were to hook up a KIB, MC60 or other suitable controller, you would gain full use of the motor.

just realize that HP is a mathematical equation, the slower a motor turns-the less hp it has the potential to make.
another way of saying the same thing is that you'll never get more HP from a slower turning motor

The MC60 controller was OEM for many treadmills and are capable of supporting a 1.5 hp motor if the correct braking resistor is used
 

whitmore

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#3
So I traded a 1/4 hp ac motor for a 1.5 hp dc treadmill motor. The treadmill motor is rated for 4800 rpm, which seemed too high to be useful, but I was planning to use it with a Focus1 dc controller,...It’s exceptionally weak at any speed.

So I hooked up an 1/8hp Dayton motor to this same controller last night, and that little booger was unstoppable at any speed. So what gives? Why is this treadmill motor so weak?
The motor's back-EMF is the speed indicator that the controller tries to regulate, and there's a pretty large correction term
for winding resistance, "IR"... in this Focus1 controller <http://www.microcontechnologies.com/files/Control Techniques/Manuals/Focus/focus_1_user_guide.pdf>
model, there's a jumper J3, with multiple possible positions, that might have to be reassigned to be
appropriate to any particular motor. Try the "IR comp" potentiometer for fine tuning.

The manual has a short section on speed troubleshooting that is probably worth reading. There's
mention, too, of different motor types.
 

Bi11Hudson

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#4
There is a good probability that the treadmill motor has a permanant magnet field as opposed to the other motor having a wound field. That's for starters. There are several issues with DC motors as how they are connected effecting the output at the shaft. You'll need to educate yourself on the subject more, there isn't room here........ by a long shot.

Now, assuming a "PerMag" field, if the rotor is ever removed from that field, the motor becomes effectivly useless. That has to do with the magnet rather than the rotor. As far as speed goes, 4800 RPM is not that fast for a "retail" motor. Consider a two pole AC motor is 3600 (minus the slip). Or a four pole AC motor, at 1800, again minus the slip. Really just a matter of sizing the pullys appropriatly.

I have a number of PerMag motors, in other than machine tool operation. Some 24 volt, others at 12 volt. For model building. But my lathe, milling machine, shaper, et al, all have AC four pole motors. Just my personal position on the subject. The important thing to remember is that as speed falls off, so does torque. Below 90% speed, the torque loss is preposterous. Definately non linear.

Another parting shot thought is that imported motors are often sized based on volts times amps, rather than proney brakes. Watts = Horsepower, et al. You can't always compare head to head that way, especially as speed falls off.

The previous post came along as I was writing. He has a very good point on the controller. That would be a good starting point.

Bill Hudson​
 
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silence dogood

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#6
It's spelled Prony brake after a fellow named Mr. Prony whom came up with the idea. Basically, you apply friction or brake to a rotating drum of a motor and measure the speed. This way you can figure out the actual working power. Generally, electric motors must build up speed, then you can apply a load. Think of a circular saw. If you press the blade against the 2x4 and then turn it on, you will get a groan or worse maximum smoke. Yet, you are drawing all sorts of current.
 

jwmay

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#7
Thanks all. I’ll connect it according to the manuals recommendations and see if anything changes.
 

Bi11Hudson

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#8
My spelling is atrocious, it is indeed "Prony". The post above covers a basic explanation of what it does.
The best I can respond is starting with my web site at http://www.hudsontelcom.com/ Scrolling down the page to Home Shop Electrics will access a PDF file of some 50 pages that will provide a starting point.

Bill Hudson​
 

silence dogood

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#9
My spelling is atrocious, it is indeed "Prony". The post above covers a basic explanation of what it does.
The best I can respond is starting with my web site at http://www.hudsontelcom.com/ Scrolling down the page to Home Shop Electrics will access a PDF file of some 50 pages that will provide a starting point.

Bill Hudson​
Bill, a misspelled word or two is nothing. You got a ton of knowledge that more than makes up for it.
 
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