oh turds! compressor motor starting cap's 'blown out' but it's a "non-standard"
Restricting my followup to rec.crafts.metalworking only.
On 2009-10-09, 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 You have a range of possible values to work with here. 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) The physical "sizes" given for most caps are a bit larger than the actual size -- think of it as a "worst case" size. I don't think that 1/16" makes any difference at all -- except perhaps in diameters (which you don't specify) so a particular clamping strap will work with it. 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? What do you mean by "daisy chain"? To me, that sounds like connecting them in series, and if you do that you will get a lower value, not a larger one. Series is: O---|(---O---|(---0 In series, add the reciprocal of the values and take the reciprocal of the answer to get your value. For example, taking a 40 uF cap and an 80 uF cap and hooking them in series, you get: 1/40 + 1/80 = 1/26.67 or 0.0250 + 0.0125 = 0.0375 1/0.0375 = 26.27 so the value is 26.67 uF. Not likely the way you want to go. Instead, you want to connect them in parallel to directly add the values. Parallel is: (View with a fixed pitch font like Courier to avoid distortion of the drawing and confusion of what it means. :-) 0---+---|(---+---0 | | +---|(---+ 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? The numbers you got from the capacitor markings show the range of values which it could take on depending on luck in the manufacturing process. I would say that probably 450 uF would work fairly well, and maybe 600 uF as well, but look for something marked about 540 uF (near the average value of the range marked on the (ex) capacitor which you have) and it will probably do quite well. Larger values would be preferred if you were somewhere where the line frequency is 50 Hz (UK and maybe Canada), while here, go for something in the range marked. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
oh turds! compressor motor starting cap's 'blown out' but it's a "non-standard"
On 10 Oct 2009 04:43:49 GMT, "DoN. Nichols"
wrote: Larger values would be preferred if you were somewhere where the line frequency is 50 Hz (UK and maybe Canada), while here, go for something in the range marked. Good Luck, DoN. Actually Canada has NEVER been 50hz. We were 25 for a few years WAYYYY back. (Niagara 1 was 25 hz) but switche to 60 across the board somewhere in the early 50s. |
All times are GMT +1. The time now is 02:45 PM. |
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004 - 2014 DIYbanter