WorldWide Drilling Resource

37 WorldWide Drilling Resource ® APRIL 2014 Getting More for Less by Britt Storkson Owner, P2FlowLLC It seems everybody is interested in getting more for less. If not, why do we have sales? Most of the time we get what we pay for, but there are excep- tions. Sometimes it’s helpful to know how to use what you have in other applica- tions so you don’t have to go out and buy something specialized (and usually much more expensive). Take motor starting and run capac- itors, for example. Why are capacitors used in motors? They are a cheap way to give the motor more starting torque and better efficiency by correcting the phase angle. Most motors use two capac- itors and a centrifugal switch to “wire” the capacitors one way for starting and “rewire” the capacitors for running. Capacitance is measured in farads in honor of Michael Faraday who dis- covered it. 1 Farad = 6.02 X 10^18 elec- trons (negatively charged ions). Most capacitors have far less capacitance and are rated in microfarads or millionths of a farad. What if you have a number of run/ start capacitors sitting around your shop, but none are the right microfarad and voltage rating for what you do? One solution: You can use two 110- volt capacitors of the same microfarad value in series, and it will double the voltage rating. But it will reduce the capac- itance value by half. So if you have two 220-microfarad 110-volt capacitors, two of these wired in series will double the voltage rating to 220 volts, but the capac- itance will be reduced to 110 microfarads. You can use a capacitance tester to verify the capacitance values. What if you have the right voltage capacitor, but need a higher microfarad value? Use two or more capacitors in parallel. The capacitance values will add up, but the voltage ratings stay the same. I’ve used this “trick” several times on motors, but I’ve found the motor man- ufacturers have some very effective ways to make you buy their replacement parts at their very high prices. The most com- mon approach is to make the capacitor a certain size that will only fit their motor mounting area without any room to spare. You will find the same microfarad and voltage capacitors in different sized con- tainers. So it’s possible to buy the cor- rect capacitor by rating, only to discover it won’t physically fit in your motor. And there is no way to make it fit. I’ve mounted the capacitors on the outside of the motor with wire ties when it would not interfere with the equipment operation or pose a hazard to something or someone. Just drill a small hole in the motor cover and route the wires through the hole using a rubber bushing to keep them from shorting to the case. If the capacitor fit is close, it is pos- sible to file off the edge of the capacitor to fit in the space provided. Most capaci- tors have a “pressed-in” cardboard lid that fits tightly in a nonconductive phe- nolic (resin/plastic) container. There is usually a ¼- to ½-inch edge above the cardboard lid which can be carefully filed down to make it fit. Capacitors are made in both polar- ized (primarily for direct current appli- cations) and nonpolarized (primarily for alternating current applications) styles. Polarized capacitors always have a polar- ity indicator - usually a “-“ stripe to denote positive and negative poles. Typically, capacitors are made by “sandwiching” a conductor with an insu- lator with a chemical “electrolyte” which acts to improve the capacitance value. The surface area of this “sandwich”, in large part, determines the capacitance value. The thickness and composition of the dielectric (insulator) determines the voltage value. Capacitors limit current (amperage). Ideally, when power is applied across a capacitor there will be zero current flow. In practice, there is always a small cur- rent flow because the dielectric is not a perfect insulator. While capacitors are fairly reliable, they do fail. Most often, they fail because the insulator breaks down from age, stress, and flaws, and they fuse together and become highly conductive (a short circuit). That’s why a bad capacitor will often blow the circuit breaker when the motor is turned on. At times, a resistor is used in series with the capacitors to limit any damage should the capacitor fail. Resistors limit voltage, which limits the current. If there is little current, the resistor acts as a conduit to the capacitor. Unlike a capaci- tor which often fuses when it fails, most of the time a resistor will act like a fuse and disconnect. In fact, “fusing resistors” are made which are designed to break the path of the current when they fail. Resistors are much cheaper than capac- itors and much more reliable. So the right information, whether it be used for choosing capacitors or get- ting a good buy, helps us get more for less. Britt Britt Storkson may be contacted via e-mail at admin@ worldwidedrillingresource.com /*% 3*-- :45&.4 /$ !& "3& %&%*$"5&% 50 5)& 8"5&3 8&-- */%6453: "354 -0$"5&% "/% 41"3&4 1307*%&% '03 &9*45*/( &26*1.&/5 > 305"3: 5"#-&4 /08 130%6$&% 8*5) -"3(& 3*/( (&"3 "/% 1*/*0/ &&% &1"*34 05"3: 5"#-&4 < 6% 16.14 < "+03 $0.10/&/54 0/?5 '03(&5 3%&3 :063 $01: 0' = 3"/4'&3 0' &$)/0-0(:> 83*55&/ #: 0)/ ? 410*3 "3,&5 /*% )0/& < "9 888 &/*%%3*-- $0. ; 9$*5*/( $)"/(&4;