I'm new to the instruction field. I've got almost twelve years in the trade with a wide variety of experience but I've never taught before, so it's been a bit of a challenge to teach myself what I'm teaching my students. I never attended trade school or anything, just went and took the MD Masters test. That means I didn't get the benefit of all that formal math training.
Here's the point to all that: In showing my students RLC circuits we found an interesting phenomenon. The power factor of a series RLC ckt. is equal to R/Z. Easy enough. But the only way our textbooks show to find PF in a parallel RLC ckt. is that it's (PF) the cosine of the phase angle. Now, I don't have access to 'scopes, or even protractors and scale rulers to do vector diagrams (the school's pretty cheap, I must say, and it's a brand new program. I'm the guinea pig.), so I needed another way to find PF in a para. RLC ckt. %Efficiency = True power over TP + Losses (R losses, in phase). TP= Apparent power (E x I) x PF, right? Right.
So, I was told that the only true power in a RLC para. ckt. are the R losses. The problem is that this always results in a 50% EFF. Example: TP = 200w (100v x 2a @ R), TP over TP + Losses (200w @ R) = .5, 50% every time. I figured this must be the wrong calculation. But then the night instr. (electronics guy) said that no, that's just a characteristic of those type of ckt.'s. OK. Good enough for me.
Then the next day my boss invades my class with another friend (also electronics guy). This guy demands to see how I'm doing my calculations. I patiently explain them and am told that I'm doing it all wrong. You have to take Ix over Ir, then the inverse tangent of that answer (which will be your phase angle), then the cosine of that. Sounds sensible enough, despite his angry attitude. Just one problem. It still comes out as 50% EFF, no matter what the PF is.
To shorten this up, suffice to say that four or five different people have assaulted me over the last few days, all with different methods of calculating PF in a RLC parallel ckt., all of which, surprisingly, work. And all of which end up giving a 50% EFF.
What the hell's going on? Is this just a characteristic of these ckt.s or am I nuts? Or both?
Can someone please explain this?
Here's the point to all that: In showing my students RLC circuits we found an interesting phenomenon. The power factor of a series RLC ckt. is equal to R/Z. Easy enough. But the only way our textbooks show to find PF in a parallel RLC ckt. is that it's (PF) the cosine of the phase angle. Now, I don't have access to 'scopes, or even protractors and scale rulers to do vector diagrams (the school's pretty cheap, I must say, and it's a brand new program. I'm the guinea pig.), so I needed another way to find PF in a para. RLC ckt. %Efficiency = True power over TP + Losses (R losses, in phase). TP= Apparent power (E x I) x PF, right? Right.
So, I was told that the only true power in a RLC para. ckt. are the R losses. The problem is that this always results in a 50% EFF. Example: TP = 200w (100v x 2a @ R), TP over TP + Losses (200w @ R) = .5, 50% every time. I figured this must be the wrong calculation. But then the night instr. (electronics guy) said that no, that's just a characteristic of those type of ckt.'s. OK. Good enough for me.
Then the next day my boss invades my class with another friend (also electronics guy). This guy demands to see how I'm doing my calculations. I patiently explain them and am told that I'm doing it all wrong. You have to take Ix over Ir, then the inverse tangent of that answer (which will be your phase angle), then the cosine of that. Sounds sensible enough, despite his angry attitude. Just one problem. It still comes out as 50% EFF, no matter what the PF is.
To shorten this up, suffice to say that four or five different people have assaulted me over the last few days, all with different methods of calculating PF in a RLC parallel ckt., all of which, surprisingly, work. And all of which end up giving a 50% EFF.
What the hell's going on? Is this just a characteristic of these ckt.s or am I nuts? Or both?
Can someone please explain this?