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Snub has more Electric Motor Questions:

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75Plus: I am wondering how the motor starts in Low and Med speeds if the coil attached to what appears to be a thermal switch is only in the circuit for High speed. One would think the slower speeds would need more help to start. The color scheme is also not what you would expect on this side of the pond. White is almost always neutral. Joe

DMIOM: --- Quote from: 75Plus on June 26, 2010, 01:29:15 PM ---I am wondering how the motor starts in Low and Med speeds if the coil attached to what appears to be a thermal switch is only in the circuit for High speed...... --- End quote --- With respect Joe, I don't think thats exactly the case.   :scratch: That aircon diagram shows the extra winding with the CFS or thermal switch as getting direct power when in high speed mode - but there's also a connection between the "left" end of the smaller winding and the "left" end of the multi-tapped winding; so whenever any of the red, yellow or white are energised, the small winding will have power applied to it - albeit via varying amounts of inductance.   And ... as the switch probably forces you to go from off via slow and medium before you get to fast, the extra inductance "to the left" of the white tap, before it connects to the end of the smaller, supposed start, winding may help act in lieu of the start capacitor ...... Dave

John Hill: --- Quote from: 75Plus on June 26, 2010, 01:29:15 PM ---I am wondering how the motor starts in Low and Med speeds if the coil attached to what appears to be a thermal switch is only in the circuit for High speed. One would think the slower speeds would need more help to start. --- End quote --- I think the switch is open at high speed and that single coil is only used at starting. --- Quote ---The color scheme is also not what you would expect on this side of the pond. White is almost always neutral. Joe --- End quote --- Brown phase, blue neutral and green/yellow ground is what we have in this part of the world. I do not think the colours in the diagram can be taken as any sort of indication for the motor that Snub has. John

John Hill: --- Quote from: DMIOM on June 26, 2010, 02:48:30 PM --- --- Quote from: 75Plus on June 26, 2010, 01:29:15 PM ---I am wondering how the motor starts in Low and Med speeds if the coil attached to what appears to be a thermal switch is only in the circuit for High speed...... --- End quote --- With respect Joe, I don't think thats exactly the case.   :scratch: That aircon diagram shows the extra winding with the CFS or thermal switch as getting direct power when in high speed mode - but there's also a connection between the "left" end of the smaller winding and the "left" end of the multi-tapped winding; so whenever any of the red, yellow or white are energised, the small winding will have power applied to it - albeit via varying amounts of inductance.   And ... as the switch probably forces you to go from off via slow and medium before you get to fast, the extra inductance "to the left" of the white tap, before it connects to the end of the smaller, supposed start, winding may help act in lieu of the start capacitor ...... Dave --- End quote --- The way I read it, if low speed is selected only the end of the tapped coil is in series with the capacitor and all the other coils are in series and connected to neutral.  When the motor speeds up the switch opens leaving the motor to run on just the single portion of the tapped coil. John

snub: Thanks for all the input.  As I mentioned at the beginning I have another 3 speed motor that will only run at one. It is an A.O. Smith. I tried searching with the model number but got nowhere. But, I did find this short technical article on their website with some good information about multi speed motors. Unfortunately, I'm not able to understand it completely. Perhaps someone could simplify it for me. "Multi-speed motors come in two basic varieties. The first variety has an extra set of windings called a booster winding that behaves like a transformer. The second variety comes with two distinct separate sets of windings. So how do these motors work? Remember from last issue how you determine motor speed by the number of poles (poles divided by the constant 7,200 gives you revolutions per minute). When the motor is under load, however, the rotating part of the motor slows down or “slips.” If the load is constant, you can increase the slip by weakening the strength of the spinning magnetic field. One way is to decrease the voltage to the magnet wire that makes up the poles. You can decrease the voltage externally by using a speed control or internally through the use of the booster winding in a multi-speed motor. In other words, the booster winding acts like a transformer, changing incoming line voltage to a lower voltage at the windings. The booster winding may come with taps that allow you to apply different voltages to the poles, creating different speeds in the motor. Remember that “speed” taps just affect the strength of the spinning field—not the actual speed—meaning you can only affect motor speed with a load on the shaft. This is because slip occurs when the load works against the weakened magnetic field. Consequently, if you bench test a multi-speed tapped motor using a tachometer or strobe, you will detect little variation between speed taps since there’s no load. Since the booster winding method of creating multiple speeds involves using a motor with just a single set of pole windings, you’ll find that the horsepower is always lower as the speed (voltage) is reduced. Consequently, this design is generally unsuitable for loads other than fans. The second type of multi-speed motor with two completely separate sets of windings allows you to use one or the other speed at a given time. Having two pole sets wound independently offers you more flexibility to produce constant horsepower in mechanical applications since you are energizing just one set of poles at a time. We also refer to a multi-speed motor “weakened” by speed taps as a multi-horsepower motor. For example, if you have a 1/3 horsepower three-speed motor, it generally would deliver 1/3 horsepower when connected to its high-speed tap, ¼ horsepower at its middle-speed tap, and 1/6 horsepower on low speed. Knowing this, you can begin to appreciate the versatility of multi-speed motors in the field. You could use the above multi-speed motor to replace single-speed 1/3 horsepower, ¼ horsepower, or 1/6 horsepower motors with the same number of poles. To achieve the correct results, simply select the correct tap and carefully insulate the two unused taps. The result would be a motor that produces the same performance, similar fan noise characteristics, and the same static pressure as the original single-speed model. Multi-speed motors give the service technician another versatile tool in the field. That's why is always good to have some in stock for emergency substitutions."

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