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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a"non-standard"
my ancient 4hp sears craftsman air compressor needs a starting
capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) |
#2
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a"non-standard"
On Oct 8, 9:03*pm, dave wrote:
my ancient 4hp sears craftsman air compressor needs a starting capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) It looks like the value of the cap is not that critical. They give you a range 485 to 580 microfarads. The average value is approximately 540 microfarads. If you order from McMaster Carr, this should work: http://www.mcmaster.com/#7245k114/=3z7b3b |
#3
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it'sa "non-standard"
I'd probably go with the next size larger (still within the specified
range), should give a bit more starting 'kick' http://www.mcmaster.com/#7245k54/=3z859g Denis G. wrote: On Oct 8, 9:03 pm, dave wrote: my ancient 4hp sears craftsman air compressor needs a starting capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) It looks like the value of the cap is not that critical. They give you a range 485 to 580 microfarads. The average value is approximately 540 microfarads. If you order from McMaster Carr, this should work: http://www.mcmaster.com/#7245k114/=3z7b3b |
#4
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a"non-standard"
On Oct 8, 10:51*pm, RoyJ wrote:
I'd probably go with the next size larger (still within the specified range), should give a bit more starting 'kick'http://www.mcmaster.com/#7245k54/=3z859g Denis G. wrote: On Oct 8, 9:03 pm, dave wrote: my ancient 4hp sears craftsman air compressor needs a starting capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) It looks like the value of the cap is not that critical. *They give you a range 485 to 580 microfarads. *The average value is approximately 540 microfarads. *If you order from McMaster Carr, this should work: *http://www.mcmaster.com/#7245k114/=3z7b3b- Hide quoted text - - Show quoted text - Roy, you're probably right, however, I wonder that if you skew the value to the higher end if you pay a price by decreasing the life of the contacts on the centrifugal switch. |
#5
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a"non-standard"
On Oct 8, 6:03*pm, dave wrote:
my ancient 4hp sears craftsman air compressor needs a starting capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) The capacitor values are a range because the caps are made with a large tolerance. Even if you got one marked exactly 580 mfd, it could actually be much smaller or much larger. I don't think Mallory has made capacitors for many,many years. One trick we used to do in a emergency is to get two DC electrolytic capacitors of twice the needed AC capacity and connect them in series, either both + leads or both - leads together and wire the remaining leads to the motor to replace a single AC capacitor. Gets you going while you look for the correct replacement. Paul |
#6
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it'sa "non-standard"
On 10/8/2009 7:03 PM KD7HB spake thus:
One trick we used to do in a emergency is to get two DC electrolytic capacitors of twice the needed AC capacity and connect them in series, either both + leads or both - leads together and wire the remaining leads to the motor to replace a single AC capacitor. Gets you going while you look for the correct replacement. That can't be safe, can it--running AC through two polarized capacitors? (Hey: two explosions for the price of one!) -- Found--the gene that causes belief in genetic determinism |
#7
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it'sa"non-standard"
David Nebenzahl wrote: On 10/8/2009 7:03 PM KD7HB spake thus: One trick we used to do in a emergency is to get two DC electrolytic capacitors of twice the needed AC capacity and connect them in series, either both + leads or both - leads together and wire the remaining leads to the motor to replace a single AC capacitor. Gets you going while you look for the correct replacement. That can't be safe, can it--running AC through two polarized capacitors? Why? You have no idea how it actually works. Look up 'Electrolytic Rectifier'. What happens when you have two series connected rectifiers, with both cathodes connected? Nothing, if you don't exceed the PIV of either diode. (Hey: two explosions for the price of one!) Sorry, but you're the biggest loser. -- The movie 'Deliverance' isn't a documentary! |
#8
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a"non-standard"
Hi!
The capacitor values are a range because the caps are made with a large tolerance. Even if you got one marked exactly 580 mfd, it could actually be much smaller or much larger. I don't think Mallory has made capacitors for many,many years. Funny you'd mention that. I bought an old furnace fan assembly ($10) and found that not only was the motor rusty inside, but the start cap was bad. The motor cleaned up well and that got it starting a lot better, but it was still stubborn at times. So I popped the cap out and looked at it. Turned out it was a Mallory capacitor. I took another look at it and said "that's been a long time". What I took as a date code suggested 1983 or 84 (don't remember which). I'm sure that little motor started up lots of times between then and now. One trick we used to do in a emergency is to get two DC electrolytic capacitors of twice the needed AC capacity and connect them in series, either both + leads or both - leads together and wire the remaining leads to the motor to replace a single AC capacitor. I'm going to have to remember that! (Or at least remember to try it and see the next time a capacitor drops out.) I'd have thought that finding a replacement capacitor for my fan would have been easy. (Find one at the hardware store, right?) Nope. Struck out at various hardware stores, Farm and Fleet (now, come on!) and only had any luck at a little hole-in-the-wall motor repair shop. $7 later I had a slightly larger "Rotom" ("motor" spelled backwards-- clever, huh?) capacitor and everything was fine once again. I was fortunate in that it did fit the capacitor compartment perfectly. If the OP can't find an exact replacement, mounting it elsewhere on the motor should be acceptable. William |
#9
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a "non-standard"
That is a common value, either of these two will work at about $8 each
http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=72152023 http://www1.mscdirect.com/CGI/NNSRIT...MT4NO=72152023 "dave" wrote in message ... my ancient 4hp sears craftsman air compressor needs a starting capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) |
#10
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it'sa"non-standard"
dave wrote: my ancient 4hp sears craftsman air compressor needs a starting capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) CDE bought the Mallory capacitor business. Take a look at this catalog page: http://www.cde.com/catalogs/PSU.pdf Thus looks to be the closest size: 460-552 MFD PSU46015A 110/125V 1-13/16" 3-3/8" http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=8523750&MPN=PSU46015A $6.15 each, 42 in stock. -- The movie 'Deliverance' isn't a documentary! |
#11
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a "non-standard"
On Thu, 08 Oct 2009 21:03:20 -0400, dave
put finger to keyboard and composed: http://www.instruction.greenriver.ed.../Shift_Key.jpg - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
#12
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a "non-standard"
"dave" wrote in message ... my ancient 4hp sears craftsman air compressor needs a starting capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) Take the old one to the Grainger's nearest you and walk out with a suitable replacement Easy. If no Grangers nearby, look in the yellow pages under motor rebuilding and they can set you up also. -- Roger Shoaf About the time I had mastered getting the toothpaste back in the tube, then they come up with this striped stuff. |
#13
Posted to rec.crafts.metalworking,sci.electronics.repair
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oh turds! compressor motor starting cap's 'blown out' but it's a "non-standard"
You shouldn't have too much trouble finding a suitable replacement from an
electrical jobber supplier.. Johnstone, or local independent electrical supplies dealer. If you have a local motor repair shop, they will know what you need by referring to the 120VAC motor voltage and 4 HP motor rating. Start capacitors need to be for AC usage, and are typically sized at about 500uF per HP. The numbers on the original cap indicate that the actual value of that series can be as low as the minimum value, or as high as the maximum value shown. The actual measured values (microfarad, or uF, or mfd) of start capacitors can vary widely, as much as about 30%, especially on parts that are decades old. The voltage rating for start caps is generally higher than the AC line voltage, and different manufacturers choose to use different rating numbers. Another common marking is 377VAC. The other source of problems in split-phase motors would be the centrifugal switch for witching between the start and run windings. -- WB .......... metalworking projects www.kwagmire.com/metal_proj.html "dave" wrote in message ... my ancient 4hp sears craftsman air compressor needs a starting capacitor, I've determined (through a process of elimination). I still have the original owners manual, and the capacitor is "part of the motor", not shown in the parts blowup, or parts list, as a seperate orderable part. further, the friggin' thing seems to be a 'non-standard' mfd rating, too (it doesn't 'fall into' any capacitor size-groups of any maker's starting cap's I can find online. matter of fact, it's not even close): the one in it now is 110 volt, 485-580 mfd mallory #139852-49 seems a slightly non-standard SIZE as well: diameter: 1 13/16ths inch, and length, overall, excluding 'spades': hair over 4 5/16ths (but clearly under 4 3/8ths) atttempts to locate same by the mallory part number on it entirely unsuccessful. so (physical size and 'look' issues aside) can I "daisy chain" two cap's and achieve the same net effect, somehow? appearance "not an issue", I just need a working compressor. I know I can replace the cap with a higher voltage cap, and that'd be fine (maybe even desireble) but what about the mfd rating? if I must, is it best to go 'bigger mfd numbers' or lesser? thanks for tips on this, guys :-) |
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