AC THEORY

[LarryFine]

dont the 2 wires in the extension cord cancel each other out . thinking of a transformer winding being one conductor

It's not just inductance. There's also normal IR losses concentrated with reduced surface area.

 

[drcampbell]

I thought this thread was going to be about air conditioning.

So start an AC Theory thread. I can answer a lot of AC Theory questions.

 

[Sberry]

I kind of did, I have to find it. I can't remember all that stuff and don't work on it enuf to get it ingrained. I need to learn

 

[LarryFine]

I thought this thread was going to be about air conditioning.

Nah. Air conditioning would be A/C.

 

[Joethemechanic]

Why are we ignoring DC ? I'm seeing more and more of it

 

[drcampbell]

Direct-current theory is a whole lot simpler.

(until you start looking at switches, fuses & breakers)

 

[Joethemechanic]

Direct-current theory is a whole lot simpler.

(until you start looking at switches, fuses & breakers)

Controls for the scrap yard magnets not only broke a 250 volt DC circuit, But they briefly reversed polarity to collapse the magnet's field faster.

 

[drcampbell]

Controls for the scrap yard magnets not only broke a 250 volt DC circuit, But they briefly reversed polarity to collapse the magnet's field faster.

Did they include a puffer to blow out the arc between the contacts when they opened? Or a strong permanent magnet to fling the arc away?

 

[Joethemechanic]

I kinda think they had a puffer but it's so long ago. Almost all of them were Square D dating back to the 60's and 70's. I remember there was a timer for the reverse polarity that you had to set to make the scrap drop off right. When they were running you could really see the arcs as it opened and closed. The cranes in the yard used 72 inch magnets. The road cranes for picking scrap up at demo sites were about half that.

These Bay City cranes were real popular for road cranes then. They were bulletproof and only 8 feet wide so you could drive them to the job without a permit. They also had an "on rubber" rating so you could run them without putting the outriggers down.

 

[jim dungar]

Controls for the scrap yard magnets not only broke a 250 volt DC circuit, But they briefly reversed polarity to collapse the magnet's field faster.

Unless it included a resistor which produced a slow degrade of the field to allowing dribbling the load rather than dumping it all at once.

Square D made and rebuilt magnets, through the 80s, as well as the controllers at their Milwaukee facility at Richard and Capitol.

 

[Joethemechanic]

Unless it included a resistor which produced a slow degrade of the field to allowing dribbling the load rather than dumping it all at once.

I think those were what we had on bridge cranes for the magnets we used for handling steel plate. Operator could pick up a stack of plates and drop them one at a time. That crane had 2 trolleys and 2 magnets. It was a really old Cleveland 20 ton. The operator''s cab moved with one trolly. It was so old that it used carbon piles Lots of span wire on that thing

 

[junkhound]

Having designed and built and troubleshot aircraft and spacecraft power systems for 55 years, could say one absolutely needs all the theory one can absorb. Wiring a house, zero theory needed, but helps.

That said however, one very rarely needs to resort to actually working Maxwell equations.

Modern day finite element programs (e.g PSpice, etc) lets you apply nearly all known theory in one convienient package.

 

[eric38]

I see the guys without any concept of theory struggling in a commercial and industrial environment, especially when it comes to troubleshooting

Was going to say troubleshooting. I moved from new installs to service, i use theory quite a bit now trying to figure out non-obvious issues. Granted its not engineering level theory, but just knowing basics is super helpful. Saw another guy say basically that you dont need to know it, till you need it. pretty true

 

[garbo]

Serious question. How often or when really would you ever need to know most things taught in AC theory levels 1 through 4 out in the field? To me it all seems unnecessary

I went to the best Vo Tech school in the area and our teacher spent more time on AC theory then anything else. Retired after 50 enjoyable years as a commercial electrician. Worked on single, two & three phase transformers, MCC'S, hundred of VFD'S and never once used AC theory. Completely forgot the rules for figuring out capacitance & inductance. Won a free lunch from a co workers electrician dad. My co worker was installing 9 or 10 post luminares every 100' on his long driveway. Can not remember if the post lights he changed over to small HID had maybe 60 or 75 VA Load . I used simple DC theory to figure out that he had to use #8 wire to first luminance then forget how many #10 guage wire to have at least 108 volts at last post luminares. My calculation was within one volt. We always had some talented union electricians on job sites and they said the same thing. I would recommend learning AC theory.

 

[Joethemechanic]

two

Are you from the Philadelphia area?

 

[zbang]

Think of these things like playing scales on a musical instrument- you're probably never going to use them to perform but learning the motions will help you play better. The AC theory will sit in the back of the brain and one day might become useful, even if you don't realize it. It also helps learn to learn, and IMHO you should never stop with that.

 

[ggunn]

Serious question. How often or when really would you ever need to know most things taught in AC theory levels 1 through 4 out in the field? To me it all seems unnecessary

The what is a lot easier to remember if you understand the why.

 

[drcampbell]

The what is a lot easier to remember if you understand the why.

The difference between training and education.

 

[Joethemechanic]

The difference between training and education.

I try to explain that to front office types, but they are too dull to understand. They think repair is like production and they can just "train" anybody to do it. They seem to think it's like training someone to stack boxes on a pallet

 

[drcampbell]

I try to explain that to front office types, but they are too dull to understand. They think repair is like production and they can just "train" anybody to do it. They seem to think it's like training someone to stack boxes on a pallet

I try to explain that to everybody. I don't always succeed.

A complex, technological society is doomed unless everybody is well-enough educated to make good decisions and fully participate.

When I was in school, we learned how to use the card catalog to find information. Today, finding information is pretty easy -- you can hardly escape the daily avalanche of information -- but we now need to learn how to distinguish information, opinion, propaganda and disinformation. And that requires a fundamental education in science, math, media, history, rhetoric and human psychology.