Somtimes My Clutch Motor Runs Backwards And Sometimes Forwards. Why?

[TinkerTailor]

so servos need rpm to make power too then. When I read about servos they say in the ads that they make the same torque at every rpm but I always suspected that cant be true.

They do make the same torque, it is the smooth change from one rpm to another that gets lost at the lower speed settings. It may not effect more expensive servo motors and may be related to the resolution of speed sensor in the controller. With the motor shaft turning faster, it can sense rpm more accurate and thus adjust it smoother when you step on the pedal.

Also, a speed reducer does not change the torque the motor puts out. A motor only has so much energy, which is a balance between torque and speed. It operates within a designed range for the load and speed most want it to be used for. We want more power and slower than they are designed for, so enter the speed reducer. It uses mechanical advantage after and independent of the motor to increase torque at the expense of speed, which was unwanted anyways.

With enough speed reducers, and assuming very little friction in the system, a sewing servo motor could lift a locomotive, it would just take a very very long time.

Edited February 25, 2016 by TinkerTailor

[DrmCa]

Can you post the pictures of your motor showing the wires and capacitor? I am intrigued!

The 3 phase motor powered from 1 phase needs a capacitor to run, and direction is determined by connecting the 3d terminal via the capacitor to the phase or ground.

Yours running in different directions with or w/o a cap makes no sense, let's see what it looks like.

I took the cover off the back of the motor and removed the capacitor. I put a voltmeter across the terminals with the meter set at 600v ac and got no reading. Then I started the motor with no capacitor and it ran the same as it did before. So the capacitor was doing nothing. I think I need a new cap to tell the motor which way to start. I dont even know if the cap that was in there is the proper cap. I wish I could get some part numbers for the cap and the wearable clutch parts. I would have a good motor then. Then I need a small motor pulley which is 15mm bore and about 35 to 45 mm diameter 3V and a speed reducter which I will make. I have been wondering why guys with the servo motors also add speed reducers? I thought the servo motor provided totall speed control.

LoveToLearn

[LoveToLearn]

It starts and runs whether its in or if I remove the cap completely and set it on the table. Sometimes it starts clockwise and other times it starts counter clockwise. It is a single phase 1/3hp 3.7 amps 1750 rpm motor. I dont see any centrifugal switch and I hear no click when its winding down when I shut it off like on the table saw in the garage.

Edited February 25, 2016 by LoveToLearn

[LoveToLearn]

tag

motor

Edited February 25, 2016 by LoveToLearn

[Art]

I guess I and most everyone else is saying to themselves that you ain't got the chops to be fooling with this thing. I am not going to tell you what to do, it is over your head. The cap you see is part of the circuit that consists of the start winding in the motor (Aux on schematic) and the start capacitor, and is switched in by the start relay (box with dashed lines), the start relay only switches in the start circuit for a short time then goes to the main windings directly. The following is usually the problem, start relay (box with dashed lines), start winding (not usually), or the start cap. On this model the cap is a 7.5 µF used as a start cap (if the schematic is correct) available at Grainger. This is as much as i can provide for you.

If the start relay is toast (probably) then it will never switch in the start circuit, and just leave the mains switched in and the motor will go whatever way it goes. Sound familiar?

Art

[Northmount]

The capacitor with its winding shifts the phase angle of the magnetic field, so that 2 rotating magnetic fields are produced in the stator and pulls the rotor around, causing it to rotate. If this cap and winding are not energized, the motor can start in either direction, or sometimes just sit there and hum. The cap and winding are commonly referred to as the starting winding. If the capacitor is faulty, or the circuit is broken anywhere between its terminals, it won't start reliably.

If you have an ohm meter, you can test the continuity of the winding and its connections. Power must be off for this test, or you'll let the smoke out of your meter. The resistance should be relatively low, probably less than 50 ohms. You may be able to test the capacitor with the ohm meter too if it is an analog type, moving needle, not digital display. With the ohm meter set on the highest resistance range, you may see the needle kick upscale and then settle back to infinite resistance. What you see is the charging current. If you reverse your ohm meter connections, you may see the needle kick to a higher value, then settle back again. You just discharged and charged the capacitor in the opposite direction. If the meter behaves like this, you can be reasonably sure the capacitor is working. If not, the test may be inconclusive, but tends to indicate the capacitor is faulty. Capacitors may have some leakage current, which is normal, so the ohm meter may not settle at infinity, but should settle at a high value of resistance.

Or instead of trying to test the capacitor, just go buy a new one, assuming you have tested the start winding and found it to be okay.

During your tests, for each component, no other components should be connected to the one you are trying to test.

Tom

Edit

I see Art has posted as I was typing this up. I agree with him. Up to you as to whether you can do any testing, safely.

[Art]

Yo, Short the cap terminals before doing anything.

Art

[mikesc]

Been a while since I last logged in, been catching up ( reading threads from 2015 over the past few days )..I agree with Art and northmount..fooling with this ( unless you really know what you are doing with electrics ) could let some important smoke out..from the meter, the motor ..or even yourself..

Buy a replacement cap and fit it..don't "test" the old one..

or..

better yet..

buy a servo motor from one of the dealers on here..

Keeping the smoke in is vital..

[Wizcrafts]

I am worried that this experiment isn't going to end well for our gentle new member...

[LoveToLearn]

The capacitor with its winding shifts the phase angle of the magnetic field, so that 2 rotating magnetic fields are produced in the stator and pulls the rotor around, causing it to rotate. If this cap and winding are not energized, the motor can start in either direction, or sometimes just sit there and hum. The cap and winding are commonly referred to as the starting winding. If the capacitor is faulty, or the circuit is broken anywhere between its terminals, it won't start reliably.

If you have an ohm meter, you can test the continuity of the winding and its connections. Power must be off for this test, or you'll let the smoke out of your meter. The resistance should be relatively low, probably less than 50 ohms. You may be able to test the capacitor with the ohm meter too if it is an analog type, moving needle, not digital display. With the ohm meter set on the highest resistance range, you may see the needle kick upscale and then settle back to infinite resistance. What you see is the charging current. If you reverse your ohm meter connections, you may see the needle kick to a higher value, then settle back again. You just discharged and charged the capacitor in the opposite direction. If the meter behaves like this, you can be reasonably sure the capacitor is working. If not, the test may be inconclusive, but tends to indicate the capacitor is faulty. Capacitors may have some leakage current, which is normal, so the ohm meter may not settle at infinity, but should settle at a high value of resistance.

Or instead of trying to test the capacitor, just go buy a new one, assuming you have tested the start winding and found it to be okay.

During your tests, for each component, no other components should be connected to the one you are trying to test.

Tom

Edit

I see Art has posted as I was typing this up. I agree with him. Up to you as to whether you can do any testing, safely.

I have already tested the cap as I mentioned. The first thing I did was discharge it. (high school electricty class capacitor demonstration). There was no discharge. Then I tested the cap and there was no continuity at any point. the cap is bulging slightly at the top. (not a good sign)

I dont see any safety issues. There is no smoke in the cap because it is dead and cant hold smoke anymore, it is sitting on a bench. The machine is not plugged in so at this moment there is no smoke in it. Im going to test the windings as indicated. If it passes ill get a new cap. Does the one in the pic look like the right specs for this motor? 350VAC and 7.5 MFA. So it is possible that a dead cap can be solely responsible for this random direction when starting? Good to know.

Edited February 26, 2016 by LoveToLearn