Myths about Electricity

I would like to start a thread about the myths of electricity.

And I have one I will talk about it in this post. If you have more Please post them
because this although causes a lot of confusion in the field it also helps our understanding
in the field.

Ever since I logged on to my first electrical forum I have seen the statements that an electric motor is completely different from every other electrical device in that if you apply less voltage it will pull more current from its source. And there is no exception or I have never seen any of the cases. But this is far from the truth.

Now before everyone automatically jumps to the conclusion that I don't understand
inductance and how coils and electromagnets work this is not true. Although I'm not a
genius in the field I do understand that inductors do not follow ohms law to the letter like resistance does.

There are some cases where if you reduce the voltage to some motorized electrical
loads the current draw to that motor will drop with the applied voltage.

If the motor itself creates the load such as a direct drive blade on a fan as you reduce the voltage the current will reduce with it. And I'm sure there are others.

Now on the other hand if you take a motor with a preset load of so much friction such
as a reciprocating pump with a piston in a cylinder which has to push the air through
small orifices and has a constant load on it created from the load itself then as you
decrease the voltage the current will increase.

I know everyone in the electrical field is not in it to understand how everything works and never will have any more knowledge than what is taught to them in electrical school and there are some who just have that drive that just have to know how it works.

To some if there instructor told them that electricity flows faster down hill than it does up hill they would believe it and never question it. And I believe if most have this attitude the electrical field will just stagnate and I hate to see this happening.

I'm not sure exactly what myth you're trying to debunk, or how; the post is a little confusing/rambling. Could you be more specific / concise?

It sounds like you've simply heard different things from different people, which may depend on their experiences. That is going to happen with everything, especially on the internet.

ACDC_comeback said:

I have seen the statements that an electric motor is completely different from every other electrical device in that if you apply less voltage it will pull more current from its source. And there is no exception or I have never seen any of the cases. But this is far from the truth.

Click to expand...

It is counter-intuitive, but this is true of AC induction motors, which is the type most electricians will be most familiar with.

ACDC_comeback said:

Ever since I logged on to my first electrical forum I have seen the statements that an electric motor is completely different from every other electrical device in that if you apply less voltage it will pull more current from its source. And there is no exception or I have never seen any of the cases. But this is far from the truth.

Click to expand...

Not sure what you are saying here. Are you saying nothing else does that? Switching power supplies do that, for example. Are you saying motors always do that? That's not true either.

Now before everyone automatically jumps to the conclusion that I don't understand
inductance and how coils and electromagnets work this is not true. Although I'm not a
genius in the field I do understand that inductors do not follow ohms law to the letter like resistance does.

Click to expand...

They do, actually. There is just an additional factor you have to add if you are dealing with parameters that change with time. But Ohm's Law still holds.

AC induction motors do draw more current when the line voltage drops. This is because the motor speed and torque is driven by the electrical frequency of the AC field, and when the voltage component gets lower, it increases slip% and shifts the current angle higher as a result.

Myths about electricity are boundless and shared whenever anyone discusses the topic, including myself.

Time for Mythbusters..



(yes, that's me with Adam Savage). It's no fun unless we get to blow something up though.

https://science.howstuffworks.com/nature/climate-weather/storms/10-lightning-myths1.htm
Ten myths about lightning. What about how it appears to come down, but the charge actually goes up? Tried unsuccessfully to convince my uncle of that one when I was a kid.

[youtube]JZUci1X-Q2U[/youtube]

Cooking With Electricity (Mr. Wizard)
[youtube]ScwbimMBklA[/youtube]

I've done the hot dog thing before. Works well.

How about a pickle?

[youtube]M9WyV72cjRo[/youtube]

That licking a 9v battery would give you the power of electricity.

[youtube]QOtacCftvcs[/youtube]

I have recently been binge watching Eric Laithewaite on youtube.
https://www.youtube.com/results?search_query=eric+laithewaite

Motors Big and Small - https://www.youtube.com/watch?v=oWiYsRi2Dss
Magnetic River - https://www.youtube.com/watch?v=OI_HFnNTfyU
Shaping Things to Come - https://www.youtube.com/watch?v=f5mA4l6xmGs

The video on electroshock therapy was interesting. I've worked on the machines they use for that. Passing about 1A through your head has to be pretty painful. It goes up to about 1,000V.

Now days they give the patient anesthesia so they are not aware during the procedure and just wake up with a scrambled head and maybe some burn marks on the forehead. In the old days, they didn't give anesthesia. It would be worse than most forms of torture.

But new research shows that the benefits associated with this treatment may actually be from the anesthetic drug (ketamine) and not from the electric shock.

liveforphysics said:

[youtube]JZUci1X-Q2U[/youtube]

Click to expand...

Is someone going to explain this video?!? Thanks!

My friend went through electro-shock therapy, he happened to end up in the pysch ward for a year and he does not remember big chunks of his life. Him, another friend and me all went out for a bite and a movie the previous day before he went haywire. I did not notice anything strange, but he happened to mention to his dad about me wanting to hurt him because he is regular height and I am tall and big. Another fella that I dont know to well frequently goes on a similar tangent about anyone wanting to hurt him, bikers, me, the fuzz, willy wonka the chocolatier...... he is pretty much crazy all the time, massive head injury, rich family, who knows how much money he wasted up his nose and down his throat.

What would be worse, the Pysch Ward or Provincial Jail...... I would hazard a guess that it would be the Pysch Ward.

fechter said:

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Stu Summer said:

Is someone going to explain this video?!? Thanks!

Click to expand...

I'd like to hear that too. It wasn't exactly clear what the voltage source was. Looked like an old TV flyback transformer in one case. Couldn't tell if it was AC or DC, but I would guess high frequency AC. How the water or oil jumps from one cup to the other is very strange. The effect on a puddle from a distance is a little easier to understand. I've played with HV stuff before and whenever you have a corona discharge it creates sort of a wind like a fan that could be enough to blow the surface around.

And back to the original question...

Ever since I logged on to my first electrical forum I have seen the statements that an electric motor is completely different from every other electrical device in that if you apply less voltage it will pull more current from its source. And there is no exception or I have never seen any of the cases. But this is far from the truth.

Click to expand...

Well, this really depends on a lot of factors. If you just take a small brushed motor and hook it to a variable power supply, the current increases with voltage unless the motor is stalled. Once you start adding electronics, like a brushless motor controller, then things get much more variable.

Take for example, a small DC-DC converter, like the kind used to power a LED light or USB charger from a bike battery. In this case, the power output is basically constant, so this makes the power input nearly constant. In a constant power setup, the current needs to increase as the voltage decreases to keep the power constant. A brushless motor controller running at the current limit will behave similarly.