How to size capacitor for capacitor run fan motor
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From: mm on 2 Jan 2010 13:21 On Fri, 01 Jan 2010 17:29:15 -0500, "Michael A. Terrell" <mike.terrell(a)earthlink.net> wrote: > >Andy wrote: >> >> On Dec 31 2009, 7:50 pm, "William R. Walsh" >> <newsgrou...(a)idontwantjunqueemail.walshcomptech.com> wrote: >> > Hi! >> > >> > > So, let's suppose you have a motor, and the nameplate is damaged to >> > > the point you cannot see what size of cap is required. Where do you >> > > go from there? >> > >> > I'd start by checking the cap that came with the motor. In the case of the >> > fan I'm talking about, the capacitor was clearly labeled as to its ratings. >> > >> > If that wasn't possible, I'd try looking the motor manufacturer up on the >> > web (either through their web site or from a web site belonging to someone >> > who sells those motors) for more information. You could also try telephoning >> > the motor manufacturer. >> > >> > Still nothing? I'd have to visit an electric motor repair shop at that >> > point. (That's the only way I know of if everything else is missing or does >> > not pan out.) >> > >> > William >> >> This can't be that difficult that we are all dependent on the keepers >> of the secret capacitor knowledge. I prefer to understand rather than >> to ask someone and then believe them. I want to know how to solve >> this riddle myself. What is the basis for capacitor sizing? There >> must be some relationship between the amount of current in the main >> winding and the current in the secondary winding. If someone on this >> site doesn't beat me to it, I will figure out how to size a cap and >> then post the solution. > > > This isn't a 'site' It is 'Usenet', even if you are using the lame >'Google Groups' interface. > > There are formulas to calculate the required capacitor. You need some >basic information to use them, so stick your smug attitude where the sun >doesn't shine. I'm just a visitor here, but I agree with Michael's reply. And Andy, why are you trying to figure out what size the cap should be when you said that the motor nameplate says 7.5 uF? I thought your question was, is it safe to use 10 uF? I think JW and Wild Bill answered those questions before your last post, and I would add that, though my info is 45 years old and probably for a different type of cap, I was told the real value for caps ranged from -10% of the rated value to +50 or +100%.
From: Andy on 4 Jan 2010 16:41 On Jan 2, 11:21 am, mm <NOPSAMmm2...(a)bigfoot.com> wrote: > On Fri, 01 Jan 2010 17:29:15 -0500, "Michael A. Terrell" > > > > <mike.terr...(a)earthlink.net> wrote: > > >Andy wrote: > > >> On Dec 31 2009, 7:50 pm, "William R. Walsh" > >> <newsgrou...(a)idontwantjunqueemail.walshcomptech.com> wrote: > >> > Hi! > > >> > > So, let's suppose you have a motor, and the nameplate is damaged to > >> > > the point you cannot see what size of cap is required. Where do you > >> > > go from there? > > >> > I'd start by checking the cap that came with the motor. In the case of the > >> > fan I'm talking about, the capacitor was clearly labeled as to its ratings. > > >> > If that wasn't possible, I'd try looking the motor manufacturer up on the > >> > web (either through their web site or from a web site belonging to someone > >> > who sells those motors) for more information. You could also try telephoning > >> > the motor manufacturer. > > >> > Still nothing? I'd have to visit an electric motor repair shop at that > >> > point. (That's the only way I know of if everything else is missing or does > >> > not pan out.) > > >> > William > > >> This can't be that difficult that we are all dependent on the keepers > >> of the secret capacitor knowledge. I prefer to understand rather than > >> to ask someone and then believe them. I want to know how to solve > >> this riddle myself. What is the basis for capacitor sizing? There > >> must be some relationship between the amount of current in the main > >> winding and the current in the secondary winding. If someone on this > >> site doesn't beat me to it, I will figure out how to size a cap and > >> then post the solution. > > > This isn't a 'site' It is 'Usenet', even if you are using the lame > >'Google Groups' interface. > > > There are formulas to calculate the required capacitor. You need some > >basic information to use them, so stick your smug attitude where the sun > >doesn't shine. > > I'm just a visitor here, but I agree with Michael's reply. > > And Andy, why are you trying to figure out what size the cap should be > when you said that the motor nameplate says 7.5 uF? > > I thought your question was, is it safe to use 10 uF? > > I think JW and Wild Bill answered those questions before your last > post, and I would add that, though my info is 45 years old and > probably for a different type of cap, I was told the real value for > caps ranged from -10% of the rated value to +50 or +100%. I am trying to figure it out because I want to understand. I think of this as curiosity. Others call it smug.
From: Andy on 4 Jan 2010 16:38
On Jan 2, 11:21 am, mm <NOPSAMmm2...(a)bigfoot.com> wrote: > On Fri, 01 Jan 2010 17:29:15 -0500, "Michael A. Terrell" > > > > <mike.terr...(a)earthlink.net> wrote: > > >Andy wrote: > > >> On Dec 31 2009, 7:50 pm, "William R. Walsh" > >> <newsgrou...(a)idontwantjunqueemail.walshcomptech.com> wrote: > >> > Hi! > > >> > > So, let's suppose you have a motor, and the nameplate is damaged to > >> > > the point you cannot see what size of cap is required. Where do you > >> > > go from there? > > >> > I'd start by checking the cap that came with the motor. In the case of the > >> > fan I'm talking about, the capacitor was clearly labeled as to its ratings. > > >> > If that wasn't possible, I'd try looking the motor manufacturer up on the > >> > web (either through their web site or from a web site belonging to someone > >> > who sells those motors) for more information. You could also try telephoning > >> > the motor manufacturer. > > >> > Still nothing? I'd have to visit an electric motor repair shop at that > >> > point. (That's the only way I know of if everything else is missing or does > >> > not pan out.) > > >> > William > > >> This can't be that difficult that we are all dependent on the keepers > >> of the secret capacitor knowledge. I prefer to understand rather than > >> to ask someone and then believe them. I want to know how to solve > >> this riddle myself. What is the basis for capacitor sizing? There > >> must be some relationship between the amount of current in the main > >> winding and the current in the secondary winding. If someone on this > >> site doesn't beat me to it, I will figure out how to size a cap and > >> then post the solution. > > > This isn't a 'site' It is 'Usenet', even if you are using the lame > >'Google Groups' interface. > > > There are formulas to calculate the required capacitor. You need some > >basic information to use them, so stick your smug attitude where the sun > >doesn't shine. > > I'm just a visitor here, but I agree with Michael's reply. > > And Andy, why are you trying to figure out what size the cap should be > when you said that the motor nameplate says 7.5 uF? > > I thought your question was, is it safe to use 10 uF? > > I think JW and Wild Bill answered those questions before your last > post, and I would add that, though my info is 45 years old and > probably for a different type of cap, I was told the real value for > caps ranged from -10% of the rated value to +50 or +100%. I'm trying to figure it out because I want to know. I didn't think of that as smug, but I guess it is. |