Danko, I found the motor's data page, and it says that it's "Impedance protected to prevent current overload (motor can be stalled indefinitely without overheating)"

Question, is the extra capacitor still needed in the circuit to obtain the rated torque?

You are lucky owning such type of motor, so you do not need capacitor in series with it.
Of course you will need extra capacitor in case if torque will smaller than needed.
Measure voltage on wind which connected with capacitor, in idle state. It will close to 115V. Then stall motor and see how voltage on wind will decrease. Maximum torque in this state will in case, when you increase capacitor 1.3uF until voltage on wind will about 115V.

 

You are lucky owning such type of motor, so you do not need capacitor in series with it.
Of course you will need extra capacitor in case if torque will smaller than needed.
Measure voltage on wind which connected with capacitor, in idle state. It will close to 115V. Then stall motor and see how voltage on wind will decrease. Maximum torque in this state will in case, when you increase capacitor 1.3uF until voltage on wind will about 115V.

Thanks for the clarification. This is important for me, and without your help I doubt I'd ever understand all this on my own. Another great thing you did for me was finding a motor whose normal market price is more than $150 dlls at just $11.00 dlls!

And yet another interesting thing: I found out that Bodine has a line of ac torque motors that may come in handy in the future for me.

 

Thanks for the clarification. This is important for me, and without your help I doubt I'd ever understand all this on my own. Another great thing you did for me was finding a motor whose normal market price is more than $150 dlls at just $11.00 dlls!

I glad my help level now is measuring in dollars. It is big progress!

 

And yet another interesting thing: I found out that Bodine has a line of ac torque motors that may come in handy in the future for me.

They inform: "Special rotor provides excellent performance for holding, winding, and tensioning applications."
Such "Special rotor" I made myself, replacing standard squirrel-cage rotor with same dimension solid iron drum. They do it in the same way.

 

They inform: "Special rotor provides excellent performance for holding, winding, and tensioning applications."
Such "Special rotor" I made myself, replacing standard squirrel-cage rotor with same dimension solid iron drum. They do it in the same way.

You used a solid iron drum? No wire or windings in it? Just like the original Tesla AC motor?

 

You used a solid iron drum? No wire or windings in it? Just like the original Tesla AC motor?

Seems Tesla invented motor with winding on rotor.
Solid rotor (iron, copper e.t.c.) was before, for example in Ferrari's induction motor.
Tesla enhanced rotor and that increased efficiency.
Motor with solid rotor have very low efficiency, but maximal initiate torque .

Edit:
Galileo Ferraris Physicist, Pioneer of Alternating Current Systems (1847-1897) Inventor of the Induction Motor

 

I just ran the small split capacitor motor for about half an hour, unloaded and freely (without stalling it), and the thing got HOT AS HELL ... what's going on?

EDIT: It's outer temperature reached about 60°C, I just measured it.

 

Decrease voltage on motor from 115 to 81...82V it will 2 times lower heating power.
For it put capacitor in series of motor. Select capacitance.
Then increase value of capacitor 1.3uF, until equal voltages on windings.

EDIT: Do all above operations with stalled motor!

 

Decrease voltage on motor from 115 to 81...82V it will 2 times lower heating power.
For it put capacitor in series of motor. Select capacitance.
Then increase value of capacitor 1.3uF, until equal voltages on windings.

EDIT: Do all above operations with stalled motor!

The only way that I see the the voltage can be lowered with what I have is to apply PWM to the motor ... I need to to redraw the circuit so I can add a pair of mosfets back-to-back, a driver, and an EMI filter ... that means that the PCB has to be redrawn and re-etched ... *sigh* ... back to the drawing board.

 

If the wire diameter is between 0,1 and 0,8 mm, then most prost cheeks with felt returns rather good results.
If the wire is over, the force will become too small, but such wire always is turned on turner bench or, (more handy) on glass-blower turner bench (eg Arnold or other). Anyway then force is given by hand as the winding cannot be very large.
If the diameter is 8mm...30 mm for ultra-high currents, especially if the wire is tabular, then the special fork is made, where forks nails are incapsulated in teflon. Works wery well. But if the wire is round, just the bench down is polstered by teflon to not scratch the insulation. The rail is doing the support work.
If the diameter is between 0,01 and 0,09 mm, this is the most sophisticated, especially under the 0,08 mm. Because the tension must be so mild, that human hand is going to be too robust. The best method is then low-inerce motor braked by DC bias. However there low inerce is the core term. The rotating mass must be not over some safety match sulphure head sized to not crush the wire. At least my young age experience with 0,01 mm wire still I remember with horror.

 

On shaft of wire spool was mounted spring brake, which prevents reverse rotation.
View attachment 151065

Reading 5 pages of a thread that is "probably already resolved" finally paid off! Since it's "back to the drawing board" maybe there is room for a suggestion based on post #10 and the numerous posts about dancers.

Let's examine the spring brake Danko employs. I have used the same concept in a roll-up projector screen that I designed. My design employed 200lb fishing line, fixed to a rigid base at one end wrapped around a wooden capstan 2-3 times, and fixed via a tension spring at the other end. In this way, it functions as a "one-way clutch," same as Dancko describes. I never considered using a spring wire instead of flexible line, but now that I've seen it, I realize a new opportunity.

If you were to take the spring the opposite way around the shaft, so that now it resists the paying out of wire, and if at the end of the braking coil you were to extend the spring straight out into an "arm," then by lifting up on this arm, you would release the grasp of the spring clutch on the shaft and permit pay-off. This "arm" could be one-in-the-same with a dancer arm.

So,

1. Wrap your spring clutch the opposite direction.
2. At the end of the spring clutch coil extend the spring material in an arm toward the takeup spool.
3. Attach a roller to the arm
4. Feed the wire under the arm roller and then to the takeup.

Now, when you start the takeup, the wire will pull up on the arm which will release the hold on the payoff shaft, allowing payoff. This should be a "self regulating" system, basically mechanical proportional control. As such it won't be as smooth as PID control. The payoff will probably start and stop (or at least alternate between fast and slow) for the whole time it is running. But I think it would work nonetheless.

Tension control could be achieved by using a weak spring (or a long spring arm) and hanging weights off the arm.

 

Reading 5 pages of a thread that is "probably already resolved" finally paid off! Since it's "back to the drawing board" maybe there is room for a suggestion based on post #10 and the numerous posts about dancers.

Let's examine the spring brake Danko employs. I have used the same concept in a roll-up projector screen that I designed. My design employed 200lb fishing line, fixed to a rigid base at one end wrapped around a wooden capstan 2-3 times, and fixed via a tension spring at the other end. In this way, it functions as a "one-way clutch," same as Dancko describes. I never considered using a spring wire instead of flexible line, but now that I've seen it, I realize a new opportunity.

If you were to take the spring the opposite way around the shaft, so that now it resists the paying out of wire, and if at the end of the braking coil you were to extend the spring straight out into an "arm," then by lifting up on this arm, you would release the grasp of the spring clutch on the shaft and permit pay-off. This "arm" could be one-in-the-same with a dancer arm.

So,

1. Wrap your spring clutch the opposite direction.
2. At the end of the spring clutch coil extend the spring material in an arm toward the takeup spool.
3. Attach a roller to the arm
4. Feed the wire under the arm roller and then to the takeup.

Now, when you start the takeup, the wire will pull up on the arm which will release the hold on the payoff shaft, allowing payoff. This should be a "self regulating" system, basically mechanical proportional control. As such it won't be as smooth as PID control. The payoff will probably start and stop (or at least alternate between fast and slow) for the whole time it is running. But I think it would work nonetheless.

Tension control could be achieved by using a weak spring (or a long spring arm) and hanging weights off the arm.

Thanks for helping me out here, Strantor. Your advice is always thoroughly appreciated. I just did another test this very moment, by turning on and stalling the motor for a few minutes. This to see if it made a difference if the motor was under load instead of just running freely. Unfortunately, the results were not very encouraging. It warmed up considerably after just 10 minutes of applying power to it.

I'm familiar with mechanical means of controlling tension to a spool of wire or film, and yes, a spring-loaded tensioning arm is still on the table. Although I'm trying to avoid it because the spool must have the ability to re-wind wire that's already been fed if necessary... I know that there are tension motors out there that I can fit the bill, but I'm a little reluctant to use them, mainly due to their cost...

I'm going to work on the PWM technique today, and then take it from there... see what happens.

Thanks again!

 

I'm familiar with mechanical means of controlling tension to a spool of wire or film, and yes, a spring-loaded tensioning arm is still on the table. Although I'm trying to avoid it because the spool must have the ability to re-wind wire that's already been fed if necessary...

Keep in mind, the shaft spring is a clutch controlled in one direction - the direction of normal operation. so there would be nothing preventing you from spooling backwards if you already have a motor on the shaft. The motor would just just be freewheeling during normal operation.

 

Alright ... I've successfuly added PWM to the tension motor, and it's behaving beautifully. One thing I noticed is that at below 45% duty cycle the motor practically loses all power and stops spinning.

But here's some pretty intersting data:

​

When the duty cycle is 100%, the voltage across blue and black is 125VAC (which is the normal reading from a nominal 110VAC outlet in this country), but the voltage across blue and red is a whooping 185VAC. The voltage across red and black is 245VAC, though that doesn't surprise me much, because the cap is contributing to that increase.

When I lower the duty cycle to 50%. blue-black reads 103VAC, and blue-red reads 114VAC

When I completely stall the motor:

• At 100% pwm: blue-black = 125VAC, blue-red = 121VAC
• At 50% pwm: blue-black = , 104,VAC blue-red = 105VAC

So it seems that the problem with the unbalanced voltage presents itself only when the motor is unloaded.

Right now I'm doing further testing, see how much the motor warms up.

One thing is bothering me a little, though. Even though I placed an EMI filter in the circuit, the thing is interfering with my wireless keyboard and mouse. Would changing the PWM frequency improve things? Right now it's working at 3.9 KHz, but I can easily adjust it to a lower or higher frequency.

I have not yet installed a second capacitor in front of the motor, as you've suggested, Danko. I still want to see how this thing performs as it is. But I will get to that point eventually.

@Janis59, thanks for your input. Those observations will very valuable once I get this thing running the way I want it to.

 

I just finished testing the motor by applying power to it at 85% PWM, keeping it stalled, and it delivered a respectable torque for one hour. Its temperature slowly raised to a more manageable 50°C. And although it's hot to the touch, it's not dangerously so.

I'll be adding a small fan to my design that will be constantly blowing air at it, just to be on the safe side of things.

Now the only thing bothering me is the EMI that's causing spurious resets on my wireless mouse and keyboard, and an external USB hub connected to my PC.

 

I've been doing some testing... and the switching frequency is definitely a factor regarding my wireless devices interference ... it seems that the higher the frequency (up to 28.8 KHz) the more trouble it causes ... I'll be back tomorrow with more observations on my circuit's behavior ... but for the time being, nighty-night ...

* zzzzzz *

 

@cmartinez,
== Your motor designed in small, closed case, specially for working in non ventilated, limited space, dirty, aggressive industrial environment.
Essentially, motor is cooling by radiation. For dissipate those 12W, surface temperature of motor must be significantly exceed environmental temperature.
See https://www.elliottelectric.com/Sta...s/Heat_Dissipation_Electrical_Enclosures.aspx
Therefore designers used wire with heat-proof insulation and silicon lubricant for bearings.
So, do not bother about motor temperature, it is absolutely normal.
Place screen (grid) shell around motor, so you can not touch it, and put it out of mind.
== Judging by your measurements, 1.3uF capacitor already selected for maximal initial torque.
== Eliminate EMI in the process of PWM with inductive (motor) load - always is big problem. I will think about it.

 

No current or voltage spikes on input and output - only small ripples:

 

I have not read through all of the postings, but I have designed a test machine that had to have a very limited torque, for testing some kind of compressors. The solution that was very satisfactory was to us a hysteresis synchronous motor and adjust the supply voltage with a variac transformer. It was completely stable and simple to set to stall at 10 inch-ounces.But it should be very possible to find a smaller motor of a similar type.The secret was in the speed/torque curve. As the speed dropped so did the torque.

 

No current or voltage spikes on input and output - only small ripples:
View attachment 152893

That's a pretty impressive circuit, Danko. I'm going to run it and play with it for a while, and see if I can thoroughly understand it.

By the way, I own one of these impedance meters. And I've just used it today for the first time to measure the motor's coils.

Here are the results of my measurements, which were performed using a test frequency of 1KHz:

• Blue-Black:
  • Inductance: 1.24H
  • Impedance: 432Ω

• Blue-Red:
  • Inductance: 1.23H
  • Impedance: 432Ω

• Black-Red:
  • Inductance: 2.48H
  • Impedance: 865Ω