ECN Forum Forums General Topics of the Trade General Discussion Area Transformers: mind-boggling, mysterious beasts

Oh, just noticed that Winnie posted the same thing, before I did!

Sorry for the redundancy!

BTW - Jon (Winny);

I really liked your Transformer explanation text!!!

That is an excellent description - may I use it in the future?

When I try to explain how they work, the words coming out are just too dang confusing to the listening party(s) - resulting in the "Deer Caught In Headlights" stare.
(words coming out resemble that of the words found in Electrical Engineering Handbooks ["Standard Handbook for Electrical Engineers - version 14" is a good example]).

Scott35

Quote:
"My guess is that your boss did feel the shock, but was probably ready for it. The current was quite low, intentionally limited by the design of the fence charger. You didn't feel the current passing through you, you felt the spark right at your earlobe."

I know I'm getting off topic here, but getting shocked was "kinda" a topic.

I think you're right. the more I think about it, I think I was "charging"....as if I was one plate of a capacitor. When we touched, I charged him.

....either that, or ambiguously mitigating radio waves refracting through a plasma polarity regurgitator.

Winnie, Scott and WFO, Thanks a lot for your contributions to this discussion.

One statement that I use alot is, "All the world's a voltage divider." When you start thinking of the human body playing a part in a voltage divider, it should probably be considered as a highly variable resistance. One day I had my Fluke 87 out and asked everyone to test for resistance by pinching the probes, one in each hand. Most results were pretty close but for one guy, whom we'll call Dave "the reptile". It was surprising to see his skin resistance more than twice as great as the highest of the rest of us. It would not be unreasonable to assume that Dave might have better resistance to electrical shock considering our observations that day. But you really need to think of humans like the reverse of the nichrome that you were trying to figure out. The nichrome's resistance per given length increases as you flow more current and heat it. Once you start getting shocked, bad things start happening that will tend to lower the body resistance, such as ionizing body fluids and increased sweating.
As far as the shock sensation is concerned, I could see more sensitive parts of the body being able sense a current flow that other areas wouldn't.
Joe

[This message has been edited by JoeTestingEngr (edited 12-23-2005).]

Sparky, I'd like to explain something not always understood, and so far not answered:

A transformer (or any power source) with a current capacity of, say, 10 amps does not force 10 amps through the load no matter what.

The voltage and the load's impedance control the possible current, to the limit iof the source. Ohm's Law comes into play: 1 volt can push 1 amp thru 1 ohm.

E = I x R, I = E/R, and R = E/I

Just like an ausio amplifier capable of, say, 100 watts, does not automatically damage speakers with a lesser rating; you have to over-drive them with voltage.

Thus, a 12v source with 10 amps capacity will flow the same current through 12 ohms as will a 12v source with 1 amp capacity: 1 amp.

I would say that Larry is right, but yet he isn't. If his 12V sources are a 12V, 10A regulated supply & a 12V, 1A regulated supply, then, of course, he is right. If his sources are 2, 12V transformers, 1 a 10A, the other a 1A unit, the 10A transformer will flow more current through the load. This is naturally the case because we know that the output voltage of the 10A TX will be more than that of the 1A TX when they are both loaded at 1 Amp.

When we design linear supplies we consider how they can handle their maximum load conditions. But we also have to consider them under no or minimal load conditions, watching for excessive voltages on the input filter.
Joe

Spark Master,
Don't think for a second that you are alone in not understanding AC and Transformer Theory.
When I first got started as an Apprentice Electrician, it all seemed like Chinese to me.
The more I thought about it, the more it made sense.
Mind you, I didn't have ECN back then either.
You guys that knock a fella like SMF have forgotten what it is like to get back to the basics.
The basics are what matter to our trade.
Yet those that would knock a guy down for not knowing about theory, can't use simple tools like a Megger or explain why it should be used.
Just my 2c worth.

I like that. "All the world's a voltage divider."

I'd also like to point out that the exchange between Joe and Larry is a perfect example of the 'refinement of approximations' that I mentioned before my transformer lecture

Larry said 'If you have 2 12V transformers, one rated at 1A and the other rated at 10A, then they will both push the same current through the load.' Which is a fine way of saying that if you apply 12V to a load, the load will carry a particular current.

Then Joe came in with a refinement: the output voltage of the transformer is _not_ constant, and will change with the connected load. It is quite likely that the output voltage of the 1A transformer will fall more than the output voltage of the 10A transformer, thus making it quite likely that the 10A transformer will put a bit more current through the load.

We could keep going further, for example looking at how transformer heating messes with output voltage, and how load characteristics change over time, at each stage developing a more complex model of the world which more closely approximates how the world works. You will find this over and over in science texts; where a good approximation is taught as 'this is how the world works', and then a couple of paragraphs later you get 'what we said previously was not quite accurate, here is the real way that things work'.

Joe, there is a story (urban legend? I have no proof, here is a Darwin Awards reference http://www.darwinawards.com/darwin/darwin1999-50.html ) of someone electrocuting themselves with a 9V source using a multimeter to measure body resistance.

Scott, you are welcome to use my text.

-Jon

Thanks, guys!

Joe, I was thinking about the body's resistance a couple of days ago, so I took my Fluke meter to check my resistance and got nothing. Then I wet my fingers and grabbed the leads, and got nothing. Am I non-conductive? I was hoping to at least be a decent semiconductor.

Can you expand on the concept that all the world's a voltage divider? Can you expand on how the human body would be a voltage divider?

Larry, thanks for your comments about having to over-drive a speaker with voltage, that helps.

Trumpy, thanks for your understanding.

SMF

Just a guess.

Meter not on auto range or wrong range selected?

Meter set to continuity not ohms?




If yes then you are truly a freak of nature.

I doubt you are non-conductive.