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Delta Rockwell band saw motor will not start
- Thread starter Janderso
- Start date
- Joined
- Feb 13, 2017
- Messages
- 2,138
An "expert" must be taken as the individual sounds that make up the word. "Ex" being a has been. And "Spert" being a drip under pressure. Further, I am not an expert, having never finished grammar school. Never went to high school but worked in the "industrial" electrical field fo well over 50 years.
That said, my experience leads me to the following disertation on the subject:
First off: "microfarad" is a common reference for capacitors, as are nano and pico farads. Milli-farads was not used until very recently, the last ten years or so. I use the symbol "u" to represent the Greek "mu" or "micro". Most "electrolytic" capacitors use "mF" or "uF" to refer to capacity. I have never seem a "milli-farad" designation. A capacitor of such capacity is normally refered to as 47,000 uF or mF. It is not labeled as 47 milli-farads. The use of 1 to 50 Farads (or larger spans) is very recent and usually for low voltage capacitors, 5 volts or so. It is an accepted fact that as voltage rating goes up, size also increases. When space permits, voltage rating is at least double, usually more, in linear power supplies.
In addition to this, there are "non polarized" electrolytics that allow the use on A-C. The 47,000 uF mentioned above is polarity sensitive and usually explodes on reverse polarity. Such filter capacitors must never be used on A-C or reverse polarity. They make great voltage stabilizers on D-C but must never be used on A-C. I have some non-polarized electrolytics on hand, of 300 uF or so and 480 volts AC. They are the size of an oil can.
Second: Motor capacitors are non-polarized electrolytics. Their purpose is to assist in altering the start winding so that there is an effective phase shift in the secondary winding. This phase shift is what allows the motor to start. Essentially a two phase motor. Not as strong as a three phase, but usable. There are motors that run the "start" winding continously, forming a second "phase". They are usually used on fans and similar light loads. They are called "split phase" motors. I do use one on a table saw, but it stalls much easier than a regular single phase motor.
I offer http://www.hudsontelcom.com/uploads/ShopElex.pdf as a text on the application of motors. It is limited, but gives insight into the phase shifting. Be advised, it has been shortened to exclude running three phase motors on single phase and generating 120-208 volts from an automotive alternator. But is still near fifty pages in length.
Electrical is a deep subject and I have barely broken the ice on the surface of the subject. Electronics and the components for it are a whole different subject. They should not be confused. Modern VFDs to run three phase motors from single phase power are quite a boon to especially hobbyists. But running three phase motors from single phase has been done since before World War One. It is not new technology. Only the VFDs use new (20 odd years) technology and their key is the variable speed. Motors run at a "fixed" speed based on the power line frequency. There are exceptions, but as a rule they are not used on machine tools because speed is not very stable. Hence, the "Variable Frequency Drives" of modern technology.
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That said, my experience leads me to the following disertation on the subject:
First off: "microfarad" is a common reference for capacitors, as are nano and pico farads. Milli-farads was not used until very recently, the last ten years or so. I use the symbol "u" to represent the Greek "mu" or "micro". Most "electrolytic" capacitors use "mF" or "uF" to refer to capacity. I have never seem a "milli-farad" designation. A capacitor of such capacity is normally refered to as 47,000 uF or mF. It is not labeled as 47 milli-farads. The use of 1 to 50 Farads (or larger spans) is very recent and usually for low voltage capacitors, 5 volts or so. It is an accepted fact that as voltage rating goes up, size also increases. When space permits, voltage rating is at least double, usually more, in linear power supplies.
In addition to this, there are "non polarized" electrolytics that allow the use on A-C. The 47,000 uF mentioned above is polarity sensitive and usually explodes on reverse polarity. Such filter capacitors must never be used on A-C or reverse polarity. They make great voltage stabilizers on D-C but must never be used on A-C. I have some non-polarized electrolytics on hand, of 300 uF or so and 480 volts AC. They are the size of an oil can.
Second: Motor capacitors are non-polarized electrolytics. Their purpose is to assist in altering the start winding so that there is an effective phase shift in the secondary winding. This phase shift is what allows the motor to start. Essentially a two phase motor. Not as strong as a three phase, but usable. There are motors that run the "start" winding continously, forming a second "phase". They are usually used on fans and similar light loads. They are called "split phase" motors. I do use one on a table saw, but it stalls much easier than a regular single phase motor.
I offer http://www.hudsontelcom.com/uploads/ShopElex.pdf as a text on the application of motors. It is limited, but gives insight into the phase shifting. Be advised, it has been shortened to exclude running three phase motors on single phase and generating 120-208 volts from an automotive alternator. But is still near fifty pages in length.
Electrical is a deep subject and I have barely broken the ice on the surface of the subject. Electronics and the components for it are a whole different subject. They should not be confused. Modern VFDs to run three phase motors from single phase power are quite a boon to especially hobbyists. But running three phase motors from single phase has been done since before World War One. It is not new technology. Only the VFDs use new (20 odd years) technology and their key is the variable speed. Motors run at a "fixed" speed based on the power line frequency. There are exceptions, but as a rule they are not used on machine tools because speed is not very stable. Hence, the "Variable Frequency Drives" of modern technology.
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- Joined
- Feb 2, 2013
- Messages
- 3,627
the centrifugal start switch may no be functioning or there is a problem in the start winding
this short video may help out...
this short video may help out...
Last edited: