/diy/ - Do It Yourself

[Anonymous No.1470316]

So Im learning a bit more about electricity, and one thing that trips me up is like...why does a lightbulb only draw the power it needs? Why is every circuit, in effect, not a short circuit?

Is this just due to the properties of the loads being used?

I guess what Im asking is: if touching hot to neutral trips a circuit, then why doesnt it trip when they are touched to the terminals of a motor?

Ive tried to ask questions like this at work. For instance, why the same motor will draw 6 amps at 110v but only 3 amps at 220v. I understand that when the voltage is doubled, you only need half the amps to perform the same amount of work. But I dont understand how the motor inherently only draws 3 amps at 220v regardless of whether or not it works on 110v. Usually the response to my question is, "It draws what it needs."

[Anonymous No.1470330]

Steel is heavier than feathers.

[Anonymous No.1470335]

Google "relationship between resistance and current"

[Anonymous No.1470341]

>>1470316
Learn ohms law

[Anonymous No.1470347]

Resistance is what limits current
A motor has resistance. When you touch hot to neutral there is no resistance R~=0
Current = Voltage/Resistance OR I= V/R
No resistance means infinite current
A "short", is when the current takes a shortcut around the resistance or load

>motor will draw 6 amps at 110v but only 3 amps at 220v
Motor wired differently, I think
Power = I*V

>"It draws what it needs."
Don't listen to that guy

[Anonymous No.1470787]

>>1470316
you're not crazy, they're really just wires, right across the hot and neutral. when you apply power they look like a short circuit for a tiny fraction of a second.
the lightbulb's resistance shoots up as it gets hot, and it'll find a balance point as long as you don't melt the glass or straight up vaporise the filament.
the motor has something seriously fucky going on, ghost magnets fucking strangle the electricity, idk.
something something VERY HARD MATH ask your mom

[Anonymous No.1470804]

>>1470316
>. For instance, why the same motor will draw 6 amps at 110v but only 3 amps at 220v.

not true unless you change the windings. some motors have terminals that allow you do do that, but if you plug a 110 volt motor into 220 volts, it will probably do something bad; it certainly will not draw 3 amps.

>>1470347
>Resistance is what limits current
>A motor has resistance.

oh yes, the 4chan expert who knows a tidbit. the current in a motor that is running is in general largely controlled by the back emf produced magnetically in the motor. what you said is only true at stall, and many motors cannot be stalled for more than a moment without burning up.

[Anonymous No.1470826]

>>1470804
>the current in a motor that is running is in general largely controlled by the back emf produced magnetically in the motor.
most people call this 'inductance'

a motor is generally an 'inductor', it resists changes in current.

>>1470316
>For instance, why the same motor will draw 6 amps at 110v but only 3 amps at 220v.
perhaps a motor with intelligent controller, vfd or something with variable input.

[Anonymous No.1470905]

>>1470316

>> why the same motor will draw 6 amps at 110v but only 3 amps at 220v

Most motors aren't like that. Simpler things like incandescent bulbs and resistors never are. You're looking at special dual voltage motor. They automatically change how the coils are connected internally depending on the input voltage. How it usually works is they default to the 110v arrangement so when you apply 220v they start to spin really fast. This triggers a centrifugal switch that changes them to the correct arrangement for 220v.

[Anonymous No.1470913]

>>1470905
>You're looking at special dual voltage motor
there's nothing special about it. dual voltage motors are extremely common.

[Anonymous No.1470918]

>>1470804
>4chan expert who knows a tidbit
Match the level of the answer to the question.
Explaining inductive reactance and impedance to someone that doesn't even understand resistance isn't helpful, it's pompous

>largely controlled by the back emf produced magnetically in the motor
>motors cannot be stalled for more than a moment without burning up
Little to do with the question

[Anonymous No.1470920]

>>1470316
An ideal voltage source will put out a constant voltage regardless of the load.

If you have ideal 120V source and connect a 100 ohm load across it you'll always get 1.2A of current flowing through the load. The reason it won't magically draw 12A is because 120V is not a high enough voltage to pushing 12A through 100 ohms. You'd need 1200V to do that. Real voltage sources behave a bit differently in that they can be loaded down causing the output voltage to drop. If the internal resistance of the source is close to the load resistance, usually the rule of thumb is R(load) < 10*R(source), then the voltage of the voltage source will drop and it'll be out of compliance.

Same idea holds with current sources too. An ideal 1A current source will push 1A through whatever load it's connected to and will develop whatever voltage is necessary across the load to accomplish that. 1A source driving a 10 ohm load? You have 10V across it. Like with voltage sources there are limitations. Current sources can't create infinite voltage. If you attach a real 1A current source to 1Mohm load you won't get 1MV across your load. Your output voltage will go as high as your current source can supply and then stop. If you have a 1A current source than can deliver 1A over 0-10V then you model it as an ideal 1A current source in parallel with a 10 ohm resistor. Your load you connect in parallel with the current source and resistor as well. You can see how if you connect a 1Mohm resistor in parallel all the current will get shunted through the 10 ohm internal resistance and almost none will go through the 1Mohm thereby capping the voltage at 10V.

I know I got a bit off topic but I hope this clarifies.

tl;dr Ohm's law is why circuits only draw the power they need

[Anonymous No.1470932]

>>1470905
>You're looking at special dual voltage motor. They automatically change how the coils are connected internally depending on the input voltage.

Just FYI, they aren't "special" (as >>1470913 pointed out, they're everywhere; 115/230 and 230/460 motors are the norm in the US), and they don't automatically switch themselves. They have a small cover that protects a set of terminals, which can be re-wired according to what kind of supply you're working with.

What you have pictured is a capacitor start motor. The extra switch, coils, and capacitor are there to substantially increase startup torque, which requires significantly higher current than the motor requires at nominal load. The switch engages (or disengages, rather) once the motor is up to speed to prevent the excessive current draw from overheating the motor.


Note that all of this is only really applicable to induction motors. The much cheaper, noisier, and less efficient "universal" series-wound/parallel wound motors found in a lot of power tools and appliances like vacuum cleaners are simply rated for a single, maximum voltage. This is ignoring the various other types of motors, too.

[Anonymous No.1470937]

>>1470932
>They have a small cover that protects a set of terminals, which can be re-wired according to what kind of supply you're working with.

Also known as a pecker head, if any anon was wondering.

[Anonymous No.1471246]

>>1470937
+1
One of many derogatory sounding names that are not so in industry. Another is a wire grip also known as a horsecock.

[Anonymous No.1471262]

>>1470932
>115/230 and 230/460 motors
well, at least in industry they are more common than internal connected coils,
it allows for some cool fuckery like downsizing inductors / soft starter by a 1/3 of their rating,

[Anonymous No.1471285]

it's the lightning goblins, they steal away all electricity that is more than the capacity of a circuit. That's why your phone drains so fast as it get older, more lightning goblins infesting your phone.

[Anonymous No.1472282]

>>1470787
For real tho, how the frick do magnets work?

[Anonymous No.1472290]

>>1472282
Summation of electric fields due to lined-up dipoles in a compound. Or something idk

[Anonymous No.1472302]

>>1472282
If Feynman can't explain it in simple terms, no one else can

[Anonymous No.1472411]

>>1472282
Gravity, Magnetism, and both types of nuclear forces are things we can observe and describe, but we can't go any deeper. Magnetism is "just there".

[Anonymous No.1472462]

>>1470316
when you flip a switch, with alternating current, the power goes back and forth between you and the power company 60 times per second. unlike water where when you turn on a valve you know exactly how much water comes out the tap, it's difficult to say exactly how much power you are getting, vs how much was lost in the power lines. The meter on your house isn't just measuring how much you use, because you share power lines with your whole neighborhood, your neighbor's usage affects your bill as well. but that's a story for another day.

so, anyway, the power is flowing in both directions not just one. It's not like you flip the switch and it "gives" electricity to the light or motor, the circuit is already full of all the electrons it can hold. closing the switch doesn't give it electrons, it merely allows the electrons to flow.

[Anonymous No.1472479]

>>1472282

You know damn well how they work.

[Anonymous No.1472501]

>>1470316
resistance. look it up

[Anonymous No.1472507]

>>1472501
so if you use 1 ought wire, a motor will spin faster?

[Anonymous No.1472518]

>>1472507
>ought

It's "aught", you god damn illiterate.

Also, technically, yes, assuming it's not a type of synchronous AC motor (which spins at a rate dependent on line frequency). However, unless the smaller wire is severely undersized, there isn't going to be a noticeable difference either way. The motor's own resistance and back-EMF will dominate as the limiting factor of current draw.

[Anonymous No.1472529]

>>1472518
>It's "zero", you god damn illiterate.
Fixed.
Uncultured slob. "Naught" if you must.

[Anonymous No.1472540]

>>1470341
this so much

[Anonymous No.1472543]

>>1472518
be nice to him he's a yuropoor that's what they teach them.

[Anonymous No.1472545]

>>1472540
also, its amazing how little I use any of the ohms law crap as an electrician... its good to know the basis of why a watt is a watts and how it relates to volts and amps ect, but I almost never need to use it.

[Anonymous No.1472559]

>>1472529

Naught is singular, Ought is plural

[Anonymous No.1472560]

>>1472545
>how little I use any of the ohms law
you do residential, you don't need to do math

[Anonymous No.1472563]

>>1472560

[Anonymous No.1472567]

>>1470316
is it perhaps because it is a resistor and resists the rest?

[Anonymous No.1473076]

>>1472563
Looks like the battery room at a telephone exchange. Except the ones I worked in used bus bars rather than cables. And 1000A fuses that wouldn't blow even when you were vaporizing your screwdriver.

[Anonymous No.1473091]

>>1473076
This or a substation service.

[Anonymous No.1473170]

>>1473076
>>1473091
It's a UPS for a server room, at a data center

[Anonymous No.1473175]

>>1473170
Yup I'd buy that as well. However if assume all blade servers. Do you know the specs?

[Anonymous No.1473223]

>>1472545
>a simple minded ELECTRICIAN ponders actual properties of electricity
>dies
let the big boys do the thinking, you keep stripping wires and leaving crimps slightly too loose so they fail shortly after your companies (((warranty))) runs out.

[Anonymous No.1473236]

>>1472282
tiny pixies that emit a bubble of iron sucking field

[Anonymous No.1473278]

>>1473175
http://eng-electric.blogspot.com/2017/03/3-performance-factors-you-must-consider.html

[Anonymous No.1473285]

R E S I S T A N C E
E S I S T A N C E R
S I S T A N C E R E
I S T A N C E R E S
S T A N C E R E S I
T A N C E R E S I S
A N C E R E S I S T
N C E R E S I S T A
C E R E S I S T A N
E R E S I S T A N C

[Anonymous No.1473316]

If I apply heat to an electric plate with a wire leading out of it, would electricity flow through the wire? Would the heat induce the flow of electrons?

[Anonymous No.1473332]

>>1472560
medium size commercial.. doing 2 buildings right now, about $500k worth of electrical. 2 1200a services, I pretty much only have to derate and pipe and box fill calcs. The size of jobs I do mean you have to have an engineering stamp and approved drawings for everything these days.. not to say I dont have to figure out what size dimmer to use from time to time, but anymore with LED drivers its a simple 0-10v dimming and maybe a powerpack relay.. the entire industry is dumbed down. I am literally just making little pipe run drawings and figuring out prefab applications so that my guys can install as fast as possible to rake the money in... but really why would I have to use ohms law to install wire, lights and plugs.. is there something special about it?

>>1473223
who says I ponder how it works, I said I rarely ever have to use it.. how can we expect you to know anything about electricity and how it works if your reading comprehension is still at grade school level.

[Anonymous No.1473341]

>>1473285
is futile

[Anonymous No.1473343]

>>1473316
Only if there is a junction between dissimilar metals.

[Anonymous No.1473379]

>>1473332
Naw just use ecalc pro

[Anonymous No.1474041]

>>1473379
I use electricians bible app. $3-4.. pretty easy and has some cool stuff like arc flash ratings and lug torques.

[Anonymous No.1474090]

>>1470787
If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.
― Nikola Tesla
He didn't pick AC for nothing

[Anonymous No.1474092]

>>1473341
who is this mono-pole di-hole?

[Anonymous No.1474107]

>>1470316
Breakers are over-current protection. Lightbulbs and motors have resistance due to a configuration that allows us to extract useful energy from the electric current.
E=IR
120v=0.5A*240(the resistance in ohms of a 60 watt incandescent)
This means a 60 watt bulb draws 0.5 amps. Most residential circuit breakers wont trip for anything less than 10 amps.

[Anonymous No.1474108]

>>1470787
>VERY HARD MATH
CEMF is not that complicated. Its a beautiful demonstration of the laws of physics, but its not rocket science.

[Anonymous No.1474114]

>>1472560
>>1472563
You are like a little baby, watch this.
>IWishIWasAllowedToTakePicturesOfTheIronMelterInductionFurnacesIWorkOn.jpg
Damn you industrial espionage and your ability to stop me from showing up anonymous strangers on the internet!

[Anonymous No.1474127]

>>1474041
Does it follow nfpa 70 or csa?

[Anonymous No.1474142]

>>1470316
Imagine electricity like water. If there's nowhere to flow, all the gallons of electricity will be dammed up and stationary.

You could have the pacific ocean and then have a little river coming off of it, only the electricity that can fit down the river will electrocute all the fish

This is why I run my wires through my hot water pipes

[Anonymous No.1474151]

>>1470787
People joke about "how the fuck do magnets work" but when you get down to the nitty gritty its still fucking mysterious, and beguiles even the most seasoned academics. Shit just works tho, so you dont have to go much farther then that.

[Anonymous No.1474216]

>>1474151
Yeah, I always felt people were missing the point. We really don't know how they f'n work, same as gravity.

We'll figure it out eventually, but for now it might as well be magic.

[Anonymous No.1474234]

>>1474216
We know more about ferromagnetism than we did in 1900. Same with gravity. It's not quite magic and we can explain magnetism in terms of what we know (electron spin and magnetic domains.)

[Anonymous No.1474235]

>>1474127
nfpa 70, and they are surprisingly fast about updating it when the new codes book is released... you should try the free version

[Anonymous No.1474250]

>>1474151
I work in a physics laboratory, and to my understanding we definitely know how magnets work. The only people who I hear say "even professionals don't know" are those who are far from being professional.

I'm a bio major working in a physics lab, so I'm going to butcher the explanation, but it has to do with the poles created by electrons within a metal around each atom.
The difference between a magnet and standard metal is the alignment of these poles. Within a magnet, they all face the same direction, and they actually have a building effect on eachother that further creates a directional EM influence on eachother.

A non-magnet metal has the poles arranged randomly due to crystallite structure, they are all in willy nilly arrangement with no building EM effect on eachother.

When a ferrous metal (a metal with electrons free to move) is exposed to a magnet, the kinetic energy comes from the influence of the aligned poles in the magnet exerting EM directionality onto the ferrous metal. The influence of the magnet forces the poles of the ferrous metal atoms to align. In this process, the metal has a "desire" to align itself into the EM field created by the magnet, the nondirectional electron poles in the ferrous metal are forcibly aligned bit by bit upon exposure to the magnet. Eventually with enough exposure, you can actually align the poles in a ferrous metal and turn it into a magnet, which is why you can turn a paper clip or needle into a magnet by rubbing it on a preexisting magnet.

Magnets are attracted to other magnets because the poles are in perfect alignment to match up with the poles on the other magnet, the pole has two ends, an "in" and an "out", which represents the + and - ends of the magnet. In order for the electron flow to compound, the magnets will align themselves accordingly, which is why a magnet will flip itself rapidly if you try and stack them the wrong way.

[Anonymous No.1474314]

>>1474250
>the kinetic energy comes from the influence of the aligned poles in the magnet exerting EM directionality onto the ferrous metal. The influence of the magnet forces the poles of the ferrous metal atoms to align.
so you're saying magnets are a source of free energy essentially?

[Anonymous No.1474459]

>>1474250
That's an explanation of how to make a magnet, not what the force is

[Anonymous No.1474516]

>>1474459
I recommend reading better.
It's one and the same.

>>1474314
Well, I'm not physics-savvy enough to answer that. I don't think so, but I don't know if the magnet loses any potential by influencing ferrous metals, whether it can continuously affect them without any cost.
Someone else here could better answer that question, I'm sure.
I do know that in magnet accelerator systems you can't really get perpetual motion, you can only extend the original momentum of the object the magnet is propelling.

[Anonymous No.1474526]

>>1472559
A zero multiplied by anything is still zero so it will never be plural, idiot

[Anonymous No.1474537]

>>1474114
there was this one anon posting a mockup of a machine he builds
i was able to tell what field and pinpoint his location to about 30 miles radius, leaving only 2 possible companies.
Blogposting is dangerous, boys

[Anonymous No.1474551]

>>1474526
you don't multiply, dumbass
you divide

1/0
2/0
3/0
4/0

[Anonymous No.1474780]

>>1474526
>A zero multiplied by anything is still zero so it will never be plural, idiot

what is zeroes? "zeroes" is the third person present tense of the verb zero.
what are zeros? "zeros" are the plural of zero.

[Anonymous No.1475541]

I've been doing electricity too, manly for when the power goes out. I was trying to run an ac unit. But that takes a lot of work because the amps needed. So I settled for now on the computer and fan got the stuff. and it worked, I just need more our better batteries. got a big solar panel too. I got a battery charger though it's easier then hooking up the solar unless you really have too. anyway far as I got.

[Anonymous No.1475605]

>>1470826
back EMF and inductance are not the same thing
the spinning rotor within the magnetic field induces its own voltage, countering the one from the supply
it's not like inductance that is just adds the imaginary part of the impedance