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| Subject - formulae | |
| colin |
I am trying to find the basic rules of transposition in large formulas,to help with studies. thank you. |
| aussiesparky | Colin what sort of formula are you trying to transpose. One good one my mum told me and it seems to work is what you do on one side of the "=" you do to the other. ie to find I when formula is V=R*I divide both sides by R so you end up with V/R = I Hope this helps Andrew |
| colin | quote: Thank you Andrew, thats just the sort of thing I am looking for.I am trying to learn the one's like, I=square rt.of W/R and W=I times it's self times R. (sorry I don't know how to draw on this thing) Thanks anyway Colin |
| Scott Vickrey | Does anyone no where a link to the formulas derived from ohm's law is online so that we may link to it? You know the old Wheel chart like on the front of the Ugly's. What is the proper name for this formula chart? |
| JimmyDee | Ohms Law, Power Chart, http://www.the12volt.com/ohm/ohmslaw.asp Another good one. http://www.electronics-tutorials.com/basics/ohms-law.htm Jim |
| JimmyDee | Electrical Calculators, http://www.the12volt.com/ohm/page2.asp Another good one. http://www.anderson-bolds.com/calculator.htm Whole page of good calculators. http://www.ifigure.com/engineer/electric/electric.htm Jim |
| Scott Vickrey | Thanks Jim, I knew we could count on you. While we are mentioning calculator sites, I'm obligated to mention what I consider to be the "grand master" of online calculator collections, who among other valuable web resources maintains an updated list of 18,535 calculators at the time of this post. Its called Martindale Center. Here's another site I just found that maintains a list of electrical engineering calculators. |
| Scott Vickrey | OK we now have our own version of the ohm's law power chart. There are also four different version so you can find one to match any situation. See them here. |
| David Madsen | Regarding fomulae, Can you tell me how I can arrive at the power consumption in kw of a 50 hp motor with only the hours of operation and the nameplate info from the motor? Thanks Dave 
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| JimmyDee | I would like to welcome you to the ElectricalKnowledge site. Amps X volts X sq rt of 3 (1.73) X # of hrs = KW hrs. (This is for 3 phase and I'm assuming because of the 50 hp) This should do it but without an actual reading of the volts and amps, it will probably be off. The name tag is for designed volts and full load amps. The likelability of either being right on, is small. Jim |
| JimmyDee | David, To determine the actual voltage and amperage of the motor you want to know the KW of usage of, you need to read the voltage at the starter. Either on the line or load of the starter is acceptable. A good quality clamp on amp probe can be used to determine actual amp draw. This should be taken on the line side of any capacitors you may have for power factor correction. If the amperage is fairly consistent because of load, (like with a pump, etc) you should be fairly accurate calculating KW usage with the formula in the previous post. Please do not do these reading unless you know what you are doing. More than likely the voltage supplying the motor is 480 volts and it is very unforgiving. After checking the NEC, Table 430.150 Full-Load Current, Three-Phase Alternating-Current Motors, it gives the full load amperage of 65 amps. So the full load KW of a 50 hp motor will be, (@ 460 volts) 53976 watts or about 54 KW hours for every hour it is run. You probably will be somewhat less than that because we tend to install much larger motors than are necessary Jim |