Need some help from the motor guys here

[nickelec]

So I wanted to get some input from some others more experienced in motors then my self,

We're trying to set up a motor station at work for troubleshooting, maintenance purposes etc. I work for a city agency doing maintenance on traveling platforms that are movable via DC motors , drives and old plcs,

Right now at the shop we have a plc set up to control a couple of light bulbs etc just to practice with peogramingt and wiring etc.

What we would like to be able to hook up one of the extra motors we have laying around to be able to play around with controls or replicate problems we have in the feild and basically learn more in the shop in a controlled environment

I believe the motors we have are DC I'm going to take some pics tomorrow and post here to get some help from you guys

Right now at the shop we have 400amp 3 pahse 4 wire feed and multiple transformers laying around step up step down if needed to make this work what other information would you say I need that I can't think of that the moment

I appreciate the help I leaned DC motors in HS using I remember using old school porcelain cone heaters old.drum switches etc the class had booths and each booths had individual rectifiers to be able to get the DC motors up and running but unfortunately I don't remember much of it lol

I'll post some.pics tom morning and try to get this going any help would be appreciated

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[gar]

190715-2344 EDT

nickelec:

Try something not too large. Possibly 1/3 to 1/2 HP at 2000 RPM and 110 V.. Look for surplus of some kind. Possibly Bodine. Bodine also has some simple motor controls without a tachometer that use counter EMF for speed information.

Electrocraft a long time ago made some motors with built in DC tachometer.

Many different companies make DC PM motors with a built in tachometer.

You need some sort of adjustable load. Could be another identical motor, some type of pump, or an adjustable magnetic brake or clutch.

The simplest motor control is a bridge rectifier and a Variac.

Some sort of tachometer.

Then work with basic DC motor equations.

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[nickelec]

I'm going to upload some pics of the motors we have in the shop I would like to be able to use what we have

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[Jraef]

To run a DC motor, you need a DC power source, like a DC drive. Do you have something like that available?

 

[gar]

190716-1702 EDT

nickelec:

If you work with motors over about 1/2 HP, then you run into power dissipation problems doing different types of tests. One HP is close to 746 W, and 6.2 A at 120 V. A 7.5 A Variac can probably drive a 1/2 HP motor close to full load.

So how to come up with load resistors, mechanical loads, controlling power components, and so on becomes a problem.

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[nickelec]

This is the motors we have we may have a drive have to check

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[gar]

190716-2051 EDT

nickelec:

A very important caution. If you loose field excitation, then a DC motor can run away in speed and really blow up. Very dangerous. You need an automatic way to remove power to the armature on field loss, or someone constantly at a switch to cut power.

I really don't understand the label, but I view the motor as too large to use for learning about DC motors.

There appears to be a 5 HP on the label. 240 V and 17,2 A is 4128 W. 4128/746 = 5.53 HP. So a 5 HP rating would tend to corrrelate. 240 V seems to be a strange value for armature voltage. Where do you get 240 V DC. Rectified 240 V AC is an average DC voltage of 240*0.636/0.707 = 215 V.

The field rating appears to be more strange at 150 V at 1.5 A (parallel connecttion), or 300 V at 0.75 A ) series connection). The peak of 120 V is 170 V, but this takes a big capacitor. Full wave rectified 240 is 215 V which is way more than 150 V.

Because I have no idea for what type of control this motor was designed I don't know why it has the values shown.

But you can play with the motor.

With a Variac and a bridge rectifier you can fully excite the field winding in parallel mode from a 240 V AC source.

With a Variac (differrent one) and a much larger different bridge rectifier you can provide armaturer power up to about 250 V if the Variac is wired to provide over voltage.

No load tests can be easy.

Connection to another similar motor could provide a mechanical loading means.

There are some ways you can measure torque without a modern torque transducer. Edison had such a means. One exists in the Menlo Park Machine Shop in Greenfield Village, Dearborn, Michigan.

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[nickelec]

They were designed for this and we still use this set up

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[kwired]

190716-2051 EDT



There appears to be a 5 HP on the label. 240 V and 17,2 A is 4128 W. 4128/746 = 5.53 HP. So a 5 HP rating would tend to corrrelate. 240 V seems to be a strange value for armature voltage. Where do you get 240 V DC. Rectified 240 V AC is an average DC voltage of 240*0.636/0.707 = 215 V.

The field rating appears to be more strange at 150 V at 1.5 A (parallel connecttion), or 300 V at 0.75 A ) series connection). The peak of 120 V is 170 V, but this takes a big capacitor. Full wave rectified 240 is 215 V which is way more than 150 V.




.

since it has 460 volt rated heater, chance is good the DC is rectified from 480/277 system, wouldn't DC from 277 be closer to 240 volts?

Is strange that field rating is a different voltage though.

OEM design rather than a general purpose motor I'd guess.

 

[Jraef]

Where the nameplate says "Wound SH", that means it is a Shunt wound DC motor, meaning the Field is a separate Shunt winding. When they show the Field as "150/300", that means it is a 300V wound Field that is split in two, so you can run it as 2 parallel 150V fields at 1.5A, or in series as one 300V field at .75A. The Armature voltage is shown as 240V, that's 240VDC. These are all common industry standard Armature and Field voltage combinations.

In a DC motor, speed is governed be the interaction of the Armature Voltage and the Field Voltage and the flux created by the Field is what retards the Armature flux, so when you LOWER the Field voltage, you decrease that retarding effect and thus INCREASE the speed. That's why a DC motor can "run away" if you lose the Field.

Torque in a DC motor is a function of the field current, so in this motor you will get more torque from the motor at the higher field current, but at a lower voltage, so the speed will be higher, unless you also lower the Armature voltage. With both factors being controlled, you can get any amount of torque up to its rated torque, at any speed up to its rated speed, and down to zero speed, i.e. 100% torque at zero speed. Up until the advent of AC Vector Drives, that was only possible with DC motors and drives like this.

In that Photo, the big orange boxes that say "IMO" are the DC drives that are creating the DC for the Armature as well as a separate source of DC for the Field (I'm assuming that because I don't see another separate Field supply unit, but your photo is cut off). In the programming of that drive is where the magic takes place in deciding how you are controlling both the speed and the torque separately.

That Joslyn Clark contactor under the left side DC drive unit is probably the DC Armature Contactor that is tied to the Field supply, so if you lose the field, it drops out that contactor to shut down the motor in order to prevent it from running away.

 

[nickelec]

Where the nameplate says "Wound SH", that means it is a Shunt wound DC motor, meaning the Field is a separate Shunt winding. When they show the Field as "150/300", that means it is a 300V wound Field that is split in two, so you can run it as 2 parallel 150V fields at 1.5A, or in series as one 300V field at .75A. The Armature voltage is shown as 240V, that's 240VDC. These are all common industry standard Armature and Field voltage combinations.

In a DC motor, speed is governed be the interaction of the Armature Voltage and the Field Voltage and the flux created by the Field is what retards the Armature flux, so when you LOWER the Field voltage, you decrease that retarding effect and thus INCREASE the speed. That's why a DC motor can "run away" if you lose the Field.

Torque in a DC motor is a function of the field current, so in this motor you will get more torque from the motor at the higher field current, but at a lower voltage, so the speed will be higher, unless you also lower the Armature voltage. With both factors being controlled, you can get any amount of torque up to its rated torque, at any speed up to its rated speed, and down to zero speed, i.e. 100% torque at zero speed. Up until the advent of AC Vector Drives, that was only possible with DC motors and drives like this.

In that Photo, the big orange boxes that say "IMO" are the DC drives that are creating the DC for the Armature as well as a separate source of DC for the Field (I'm assuming that because I don't see another separate Field supply unit, but your photo is cut off). In the programming of that drive is where the magic takes place in deciding how you are controlling both the speed and the torque separately.

That Joslyn Clark contactor under the left side DC drive unit is probably the DC Armature Contactor that is tied to the Field supply, so if you lose the field, it drops out that contactor to shut down the motor in order to prevent it from running away.

If you ever get to NYC let me know we can use a guy like you to show us a few things in regards to these drives and the set up we have

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[gar]

190717-1944 EDT

nickelec:

I would describe the torque speed relationship as follows:

1. Torque is determined by the load. Whether the motor can supply the required torque is a function of the motor.

2. Motor speed is determined by source voltage minus the voltage drop internal to the motor resulting from the mechanical power load on the motor.

3. For a fixed field flux density, constant field current, the motor torque is proportional to armature current.

4. For fixed field flux density the generated counter EMF is proportional to armature RPM.

5. For said conditions as motor torque load increases armature current has to increase, and thus counter EMF decreases meaning motor slows down. It is all a balance of different variables.

6. If we lower the field flux density under very light load conditions, then the speed has to increase to supply the needed counter EMF.

7. On the other hand if field flux is reduced, then for the same torque it is necessary to increase the armature current, and in turn speed is reduced.

I still recommend that you work with a much smaller motor and associated components.

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[gar]

190717-2219 EDT

A full wave rectified sine wave has an RMS value equal to the RMS of the sine wave without rectification, and this is 0.707 of the sine wave peak. Whereas the average value of a sine wave is 0, and the average of a full wave rectified sine wave is 0.636 of the peak, and for 1/2 wave rectification it is 0.318 of the peak.

Thus, the ratio of RMS to average for this case is 1.1116. 240 V full wave rectifier is 240/1.1116 = 215.9 V average DC. Or at 120 V it is 107.9 .

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[gar]

190718-1056 EDT

To add to my post #12.

8. If you want to maintain the same mechanical power output at the same speed after reducing the field excitation to a lower flux density, then this means the same load speed and torque are required. In turn that means source voltage must be increased.

Maintaining the same mechanical power output means the mechanical load determines this power.

Current automatically adjusts to the demands of the load torque. Something needs to adjust source voltage to achieve the desired output RPM.

With electronic speed control of a motor there is needed something to measure speed, typically a tachometer attached to the motor, but it could be motor counter EMF, and this signal is fed back to adjust motor source voltage.

Usually there is over current limiting as well as speed control. This limits torque.

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[Besoeker3]

190716-1702 EDT

nickelec:

If you work with motors over about 1/2 HP, then you run into power dissipation problems doing different types of tests. One HP is close to 746 W, and 6.2 A at 120 V. A 7.5 A Variac can probably drive a 1/2 HP motor close to full load.

So how to come up with load resistors, mechanical loads, controlling power components, and so on becomes a problem.

.

One way of testing:
You could run two DC machines back to back, one motoring, one generating.
That's something we regularly did when DC was the more common way of producing a variable speed drive.

 

[gar]

190718-1224 EDT

Besoeker3:

I mentioned that in post #2.

With small surplus components it should not cost a lot to make a good experimental setup.

.

 

[nickelec]

Would anyone be willing to draw up a sketch for me?

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[gar]

190719-1624 EDT

nickelec:

A motor/generator like the following is quite inexpensive, and might be good for experiments. It is a permanent magnet field type. Might require external blower for cooling, especially for low RPM, as do all motors.

https://www.surpluscenter.com/Elect...-Fitness-Treadmill-Motor-F-174504-10-3039.axd

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[gar]

19071-1943 EDT

When I made the last post there were 12 motors, now none.

If you search for treadmill DC motors you will find many. Look for low cost, you don't really need quality. Your experimental service will be very limited. Use one as the motor and a second as a brake load (generator to a resistance, light bulbs).

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[Jraef]

There are 4 different treadmills on my local Craiglist today, all in working condition, totally free to whomever comes to haul them away.

I wonder just how many of those things are bought, used for a week, turned into a clothes rack for a few years, then junked. I'd bet it's 90% or more...