# How do I test a 90VDC treadmill motor?



## heartmd (Apr 14, 2009)

I have taken the motor off the treadmill. Open enclosure, 1.25HP, external fan motor.
Thanks


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## J. V. (Jun 1, 2007)

If it's a two lead (wire) permanent magnet motor like I suspect it is, do the following checks.

Apply 90 volts DC to the motor. If it runs, the problem is in the DC controller (drive) or controls. 

Check to see if you have voltage at the input leads for the motor. (the wires that the motor were connected to). The treadmill must be set to run full speed to see 90 volts. This voltage will vary with the speed adjustment on the TM.
If you have no voltage present, the motor is most likely not the problem.


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## Yoyizit (Jul 11, 2008)

You need 7 ea. 12v car/motorcycle/lantern batteries in series for a full voltage test. 4 ea. might be enough to start the motor, or keep it running after you spin up the shaft.

What tests do you want to run? Speed, torque, power?

If you want to vary the speed and still have low speed torque you need a controller like the treadmills have.


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## J. V. (Jun 1, 2007)

Yoyizit said:


> You need 7 ea. 12v car/motorcycle/lantern batteries in series for a full voltage test. 4 ea. might be enough to start the motor, or keep it running after you spin up the shaft.
> 
> What tests do you want to run? Speed, torque, power?
> 
> If you want to vary the speed and still have low speed torque you need a controller like the treadmills have.


7 batteries when he can measure the output voltage on the treadmill. If he has no output for the motor, chances are very good the motor is not the issue. You sure do like to complicate things don't you?
Can't you see the OP would not even know what your talking about? You think he actually knows what "series" means? Torque! :whistling2:


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## Yoyizit (Jul 11, 2008)

J. V. said:


> 7 batteries
> no output
> like to complicate things
> Can't you see
> ...


"How do I test a 90VDC treadmill motor?"

"Ask and ye shall receive". 
The OPer or OPess can further ask for clarification if necessary [as can you]. . .

I guess I should also state that whatever method I may suggest is not meant to contradict other, equally valid, methods, but to complement them. This way the OP gets a menu from which to choose.

Since you are interpreting my behavior ["like to complicate things"] I now have license to interpret yours. 
In a roundabout way, you may be placing too much importance on what I post.


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## Ultrarunner2017 (Oct 1, 2008)

Hi;
Some motor controllers will not output a voltage without a load, or may show full voltage even if the controller is blown. 
To properly test, the motor should be properly connected to its controller, then tested with a DC voltmeter or an oscilloscope.

When the motor is running at less than full speed, the motor should receive a pulse-width modulated signal that will reach full voltage, but for shorter than the full cycle period. This is how DC motors are controlled to have high torque at low speeds.

If I had to put money on it, I would put it on the controller. The electronics are much more likely to fail than the motor is.
If it's a very old TM, then the motor brushes could be worn out, or worse, the commutator burned up. It could also be a motor bearing, but that's easy to test; Just try to spin the shaft (with the belt disengaged). If it spins, it's not the bearings.

Be careful if applying power to the motor while it is dis-mounted from the TM.
First, the motor runs on 90VDC, which can shock you nearly as badly as the 115VAC line can!

Another consideration is that; if the motor starts, it will jerk, and roll away, taking with it all the wiring and other equipment that is connected to it.
Best thing is to just disengage the belt and test with it still mounted to the frame.

If you are familiar with electricity, I can recommend another way to test the motor, but I won't disclose this unless you, the OP is confident you can handle it.

FW


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## micromind (Mar 9, 2008)

A 90 volt DC motor will turn with 12 volts applied, provided it is not turning anything else. It won't turn very fast, and will have limited counter-torque. You'll be able to hold it with your hands. If it turns at all on 12 volts, it's likely OK.

Don't short out the car battery, it can come up with lots of current. It can't shock you, but it certainly can burn you! Don't make a spark near a car battery. Car batteries make hydrogen gas, which is explosive. It can blow the top off the battery, and spray you with acid. 

Rob


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## Ultrarunner2017 (Oct 1, 2008)

Take the motor out to the car and hook it up with a pair of jumper cables, rather than bringing the battery inside.
As stated by micromind, be very careful not to short the battery.
Hook jumpers to the motor before attaching the other ends to the battery.

FW


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## InPhase277 (Feb 9, 2008)

KE2KB said:


> Take the motor out to the car and hook it up with a pair of jumper cables, rather than bringing the battery inside.
> As stated by micromind, be very careful not to short the battery.
> Hook jumpers to the motor before attaching the other ends to the battery.
> 
> FW


And keep your foot on the motor when you apply power, because if it works, the body will tend to rotate instead of the shaft. Also, if you have an automotive battery charger it would be easier to use in this case than the car battery.


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## J. V. (Jun 1, 2007)

KE2KB said:


> Hi;
> Some motor controllers will not output a voltage without a load, or may show full voltage even if the controller is blown.
> To properly test, the motor should be properly connected to its controller, then tested with a DC voltmeter or an oscilloscope.
> 
> ...


 Never heard of PWM in the same sentence as DC motor control, only AC motor control.
Look at a DC output (vs) a AC simulated sign wave (PWM) with a scope and tell me what you see.
Agree, the best way to test motor and controller is to test them connected. But testing each seperately is SOP. Then connecting for fine tuning of the controller.


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## Ultrarunner2017 (Oct 1, 2008)

J.V.;
If you want to run a DC motor at a slower speed but maintain torque, how would you do this without modulating the on cycle?
PWM, from what I have learned is not AC. It is pulse modulated DC.
Waveform never goes below 0V, where in AC, the wave goes both above and below 0V.

FW


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## Yoyizit (Jul 11, 2008)

http://en.wikipedia.org/wiki/Pulse-width_modulation


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## Ultrarunner2017 (Oct 1, 2008)

Yoyizit said:


> http://en.wikipedia.org/wiki/Pulse-width_modulation


I'm reading the article, and checking other sources, and from what I can see, PWM works for both DC and AC motors.
The calculus in the article has jogged some very rusty wheels in my brain<g>

FW


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## J. V. (Jun 1, 2007)

DC circuits do not have cycles/Hz like ac. If you look at a dc output on a scope it is a flat line. If it's not, the output is corrupted. Simple electronics. 
I will say I have not been working for awhile, so new things may have been introduced. But, simple laws of electricity never change.

PS.....DC motor speed control is accomplished by varying the voltage, while varying the speed of an ac motor is accomplished by varying the voltage and frequency proportionally. This where PWM comes into play.


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## Ultrarunner2017 (Oct 1, 2008)

J.V.
I think that we are having a disagreement of terms here.
I should not be referring to PWM as DC. DC is a constant voltage.
PWM is pulsed, but at the same time, it does not have to be AC.

What I was referring to as a DC PWM is a signal that switches between some high voltage and some low voltage (not necessarily 0V)
For a DC motor, the signal would be PWM while the motor is accelerating or decelerating, but straight DC at other times.

I have worked with PWM systems where, when scoped, the signal looks like logic pulses when the motor is accelerating and decelerating.
As the motor speed is increased, or its load is reduced, requiring less torque, the waveform changes. Now, the on, or high part of the pulse increases, and eventually all you see is a DC line.

I have seen controllers that used a pre-set DC voltage and PWM to accelerate and decelerate from max, and those where the DC voltage varies as well.

Thinking about all of this, I'm starting to wonder whether the treadmill would even have a use for PWM.
A DC motor should work fine. The motor starts at some minimum speed, and any changes in speed are gradual, so torque should not be an issue.

It has been a while for me too, and I don't own an oscilloscope anymore. I no longer work in electronics, maybe for the better

FW


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## J. V. (Jun 1, 2007)

DC motors are comprised of an armature and a field. The field can be a magnet or wound like an AC motor. DC motors come in a few different variations. (For another day). The armature receives the DC voltage and the field repels it. That is why it turns. By lowering the DC voltage to the armature the motor will slow down. When the voltage increases to the armature the motor speeds up proportionally to the voltage. This is how you *basically* control a DC motor.
The DC motor can achieve higher base (nameplate) speeds by whats called field weakening. Lowering the field voltage. This is very basic DC motor technology. This what I know, and I do not know everything. 

AC motors are comprised of a rotor and stator. The rotor is built with iron bars and looks like a single barrel of iron. The stator looks very similar to a wound DC motor field depending on the motor.
To achieve suitable speed control of an AC motor you *must* proportionally adjust hertz and voltage. For example. 460 volt, 1800 rpm, 60 Hz motor. If you apply 460 volts at 60 Hz the motor will run at base (nameplate) speed, 1800. If you apply 240 volts at 30 Hz the motor will run at 900 rpm. If you apply 120 volts at 15 Hz the motor will run at 450 rpm.
This is where *Pulse Width Modulation comes into play.* AC inverters (VFD's Drives) input AC voltage, then convert the AC to DC. It is stored in the DC bus (800 volts DC at 460 volt AC input) The drive then uses whats called IGBT's, capacitors and logic to transform this DC voltage into a simulated AC signwave. This is PWM at it's most basic description.
Keep in mind all the values above are expressed in general terms and can fluctuate a few volts and rpm's here and there.

Thats all I have my friend. Let me know what you think........John Valdes 

http://www.electriciantalk.com/f28/ Check this forum out. We can discuss this further there. This is a DIY forum and I think this discussion should go there.


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