What's the point of a relay?

The switch has a low current rating, the relay has a high current rating. It means the key switch doesn't need to be rated for a thousand amps.

Less amps going through the switch

it means not much power goes through the switch.
something like a starter motor draws an absolute shitload of current and running several hundred amps through a wire to a switch, through a very heavy duty switch, then back to the motor needs a lot more wire than a tiny switch into a relay

you guys are horrible with examples

a relay allows you to switch on a device without maintaining a active load

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>>61017677

You can use a relay with a modest voltage (i.e. 120v) to control a three phase motor in forward or reverse.

>>61017677
Why are you so stupid, OP?

>>61020852
Two options: stupid or evil.
Evil is more likely on 4chan, but not much more likely.
Sometimes both.

>>61021004
>>>/leddit/

>>61017777
What?

>raining, got soaked
>time to turn on my car
>*BZZZ ZAP*

OP is dead

>>61017677
Why not ask your mom, the undisputed king of blowers.

>>61021091
he means so that there isnt like 20 amps going thru the switch's contact that are like 2 inches from your fingers and are typically small and flimsy

>>61017677
It's like a bigass mechanical transistor.
Not like this would say anithing to the OP...

>>61017677
Inductive load
arching
going to have a bad time

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>>61017677
Former mechanic here and computer engineer. It's for several reasons. It's to reduce mass by reducing the gauge of wiring needed for circuits. The number one reason now a days would be it allows a computer/micro-controller that is using 5 volt logic to control a device that uses 12-14 volts DC. It's also has the benefit of dissipating very little heat compared to a solid state switch for high current loads. The solid state devices often need air blowing over them and heat-sinks to keep them cool. The HVAC systems on most cars have switched to using a solid state driver to vary the blower motor speed. They'll be housed inside the hvac housing itself and use the blower motor fan to cool itself down.

>>61017677

cuz then you are the switch

>>61021337
>>61021725

12 volts of DC
wont hurt you like that. The relay allows manufacturers to use lighter gauge wires and cheaper switches in the cabin. They also allow the modules in the car control 12 volt circuits with 5 volt logic.

>>61021922
A USB port is only 5V and carries enough current to stop your heart.

>>61022036
You need enough voltage to overcome the impedance of your body to induce enough current to kill you.

>>61022036
>A USB port is only 5V and carries enough current to stop your heart.
dunno about that anon

>>61022036
samefag as >>61022048 here.

Don't take my word for it. Check this video out of a guy that likes to shock himself for views and he happens to be an electrical engineer.
https://www.youtube.com/watch?v=XDf2nhfxVzg

You can also learn about how ohm's law fucking works.

>>61022048
>>61022076
This is true

>>61022065
>100-200mA can be fatal
>standard USB port carries 500mA

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>>61022094
You must be talking about some kind of stupid special condition where someone gets in a salt water bath and plugs a USB into a 5volt transformer in a wall then strips the cables and spreads them out and places them on each side of his heart then gets lucky as fuck and does not trip anything or any built in fuse or safety in the USB transformer and arcs his heart and dies

Kind of like how you can drown in a cat's water bowl technically if you set up the right conditions

>>61022076
>>61022048
And because of this fact that's why 12 volts is still used in autos. There's very little special training needed to handle 12 volt wiring and batteries as it's considered to be a non-lethal voltage. Technicians that work on hybrids and EVs need special training and all high voltage circuits are clearly shown by being wrapped in orange electrical tape and the connectors themselves are orange as well.

>>61022129
I never said it was a practical way to die, I was just pointing out that a mere USB port carries the current it takes to kill you.

>>61022140
and a bullet contains the lead needed to kill you. It's a stupid point to make.

>>61022158
It was worth making, voltage isn't what kills you. You can take a 10kV shock no problem. Hell, tasers are generally 50kV.

>>61022179
people with guns don't kill. It's the lead projectile that's massive enough that does.

I can shoot you with a bb gun all day and it wont kill you.

>>61022211
People have died from getting shot with a single BB before.

>>61022248
people have died from tazers.

>>61022263
Neat

>>61022271
>voltage isn't what kills you.

Please take a course on even basic electricity. You need voltage to even have current. You don't understand even the most basic concepts of DC circuits if you don't understand this. To have current without voltage would require some superconductor that living humans are not.

>>61022311
I know basic electricity, you cunt.

badly drawn but whatever ( i know how relays work, but its not drawn right here, I know...)

instead of running 100A through the dash (if its a car) you only really need to run .1A to turn it on or off. Its like a mosfet but not variable.

There is no way you can get 100A running through your headlight stalk without it melting and catching your car on fire.

>>61022327
Lol, then calculate the load of a 500k resistor at 5 volts and reflect on what you said earlier.

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>>61022372
forgot image,

>>61022373
Look, you little bitch, all I was saying is that "lol its just 12 volts xD" doesn't mean shit.

>>61022396
You're so full of shirt. Lol, go to bed.

>>61022410
no

>>61017677
Honest answer OP. Relays are so fucking cheap now that they're used as a way to cut cost. This is why you rarely if ever see high quality switches on anything anymore. In a car it lets you use extremely cheap wires for the switch.

There's very few circuits that need a real mechanical relay.

>>61022396
Amperage is determined by the voltage and the impedance of the load. The current rating on a power supply is just the amperage it will support up to.

>>61022437
Refer to
>>61022468

Go to bed and learn what ohms law means tomorrow.

>>61021634
Bazinga

>>61022457
Side note.
Are "solid states" that this anon >>61021758
refers to mechanical switches?

Would these be suitable for outdoors use if in a case prepped for the elements?

I'm looking for something more durable for long term use.

>>61022525
You'd have to read the datasheet. There's relays for everything.

>>61022468
No shit.

>>61022482
I know what Ohm's law is.

>>61022525
Relays are great for cheaply controlling a large amount of current. Solid state would be something like a mosfet or an amplifier. If you're dealing with varying voltage or pulse width modulation you need to go solid state. If you're just switching something on or off every once in a while relays are ideal.

>>61022587
K, then you don't understand how it works then.

>>61022640
Yes I do.

>>61022661
K, then how many amps would pass through a 500k ohm load at 5 volts?

>>61022683
10µA

>>61022745
K, now you should understand why the point of the amp rating of a 5v usb charger is completely irrelevant. The impedance of a human ranges from 500k ohms to several Mohms.

>>61022795
It's entirely relevant when I'm pointing out that something delivering 12V is perfectly capable of lethality.

>>61022795
On top of this a body has capacitance that will resist DC current.

>>61022822
No it's not. You just proved it's not. Run the calculation again with 12 volts. You seriously just did the calculation that shows 5 volts won't be lethal to a human.

>>61022852
100mA can be lethal, a standard USB port delivers 500mA.

>>61022137
Mechanics want to get shit done quickly too, since they are paid a "flat rate" per hour a job is rated

Which is why i've said fuck it i don't care if this battery can push enough amps to sizzle me crispy i'm gonna jump this bitch in the rain and hope there's enough tread on my shoes to save my shit

>>61022866
Your cognitive dissonance is amazing or you just used an online calculator and have no idea what youre talking about. A usb port won't deliver 500 ma through a 500k load. You just calculated that...

>>61017677
>why don't you just turn the switch and have the power go directly into the motor
Why don't you stick your phone directly into the hydroelectric dam? It's more direct.

>>61021922
Inductive loads will generate whatever voltage they need to keep the current going.

>>61022903
Or I'm just fucking with some dumbass that's getting his panties in a bunch over nothing.

>>61022941
>>61022941
Inductors generate voltage when the magnetic field collapses. You need a.c. current or a pulsed circuit to generate more voltage through an Inductor. Continuous DC current won't do that. A 12 volt battery is continuous DC current. Your comment makes no sense in this context.

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12 volts can be lethal if it starts a fire or scares the fuck out the driver and the driver drives over a cliff.

I think it highly relevant to point out most modern cars run most of the electrical bits off ground now days.

>>61022992
How does the standard Kettering ignition system work then?

>>61022140
So do powerlines yet birds can rest on them just fine. What matters is voltage difference between you and the thing you are touching

>>61022076
why its a poojet

>>61017677
A couple of reasons.

1. Motors are inductors, when introduced into a circuit they can induce large voltage spikes that disrupt or damage sensitive electronics

2. You can use small gauge wire for control circuitry which can be highly complex and require a lot of wire and use heavy gauge wire just for the short straight run to the motor

3. Its better for personnel safety if they almost never have to be directly exposed to high voltages so you physically separate them from the high voltages with dedicated control circuitry with very low voltages that are less hazardous.

4. It's easier to diagnose problems that might be in the control circuity when you can safely shut down and lock down the machinery it drives and test the circuit independent of the machinery.

>>61026986
Oh I forgot the most basic thing, driving a high current device from a low current device like a microcontroller

>>61024339
With pulsed DC current. That's why you have a device called a distributor that controls the timing and dwell.