How does an appliance that is plugged into a wall socket limit the amount of current it draws?

Question

I'm designing a project to work that is plugged into a wall socket (in the US). Does the appliance automatically draw whatever it needs? If that is true, does that mean you could take out the batteries of a remote control and plug the connectors to the batteries into a wall socket and not have it get fried? How exactly does it work?

Answer 1

The electric socket has the ability to send through massive amounts of amperage (current) but in a way only uses what it needs. The rules would follow simple electronics rules and theories, which I'd think would apply to any country. The electricity is limited by power supply (step down transformers) in the device usually. Example, a clock radio. Doesn't use very much electricity, however, the clock's internal circuitry would fry if it were to be connected directly to the full electricity available from the wall socket. Instead, the plug goes directly into a step down transformer, thats inside the radio, and from there, the radio's circuitry then only is using 5-12volt of electricity.

If you were to try to plug the connector's from a remote control directly to the wall plug, then you'd have a big poof of smoke instantly. That is because electricity takes the path of least resistance. The resistance would only be a micro millimeter of wiring. No resistors, no step down transformer, would mean that massive amounts of amps would try to travel through those thin wires and eventually create a short circuit by frying the small wires.

So, in a way, appliances do draw what they need, but the electric socket is ready to send as much as anything could possibly draw. There has to be some sort of thing to limit the draw though. Resistors, step down transformer (for small electric devices). Now big appliances, don't have step down transformers or resistors. But they still only draw what they need.

Answer 2

First of all, there is a voltage difference between the battery powered device (usually about 3 volts) and the power coming out of the wall (usually about 110 volts). As one hundred ten is bigger than three, plugging a three volt device into a wall socket will definitely fry it! Plus the fact that the wall voltage is alternating current, while the battery powered device is designed to take direct current only.

It depends on the design, but usually an appliance draws however much power as it is consuming. The very act of causing an electric motor to rotate causes it to generate its own power (back emf) which opposes the electrical current that created it. The faster the rotation, the greater the back emf, which serves as an inherent speed limiter, since at some point the forces balance each other. Also, electrical circuits have internal resistance built in, both inherent resistance and electrical resistors purposefully put in, that limits current flow.

Most appliances have a power supply circuit that converts A/C to D/C. These power supplies often have a transformer that isolates the plug from the rest of the electrical circuits inside the appliance. The magnetic core within the transformer saturates at a certain magnetic field strength, which puts a limit on the maximum amount of current that can flow through it.

Answer 3

The device must be designed to used the voltage applied. A washing machine, a electrical light bulb are both designed to operate at 120 Volts AC. That is standard US voltage. When you plug one of these items in the electrical outlet, they draw the amount of current they need. If you for some reason had a 10 amp fuse or circuit breaker in your electrical panel, they would probably fail due to over current. That is why most house hold use 15 or 20 amp fuses or circuit breakers. The remote you mentioned above probably uses 2 1.5 volt DC batteries. The electricity in your house would fry burn up the device as soon as your applied the power. The are rated for 3 volts DC not 120 volts AC.

The motor in the washer and the compressor motor in the refrigerator were designed to work at say 12 amps, and 120 volts.

Unless there is a malfunction, they will not pull more.

Answer 4

Many smaller devices, such as the clock radio, your cell phone or shaver charger, or tv remote use DC (direct current). In the case of the radio or charger, like said above, use a step-down transformer to 'step-down' 120VAC (alternating current) to 24VAC or even lower depending on device. Then to convert the AC voltage to DC, a rectifier is used (allows current to travel in only one direction). There is more to a rectifier than that, but hope it gives you an idea. In the case of your tv remote, it uses between 3 and 6 Volts, depending on how many batteries it holds. Batteries are DC, so a rectifier is not needed. But if you were to take the wires off of the batteries and stick them in the wall, it will fry the internals, because they were designed for a small DC voltage source, not 120VAC.
A lightbulb can be run on either DC or AC, since it is just simply a resistance. The light is created by a large amount of current running through a filament, causing it to get hot and glow. The amount of current is regulated by the resistance of the filament, or the wattage rating of the bulb.
Appliances pull the amount of power that they need. Your house outlets are regulated so that if something went wrong with the appliance, that circuit will shut off by a breaker 'tripping'. By electrical code, usually your house outlets are rated for 15 Amps, except for electric stoves and refridgerators, which are rated for 20 Amps. So if you were to plug in 20000 lightbulbs into your wall it would trip the breaker.

Answer 5

No, it's not quite that easy but it can be done. The appliance is much like you at the dinner table. You only eat as much as you want. Regarding your remote control, you would have to build a circuit that when plugged into the wall outlet, would duplicate the batteries.
You would need a transformer to reduce the house current from 120 volts to 3 volts. Then you would need a diode to change the alternating current to direct current. Finally you would need a capacitor to smooth out the ripples in your 3 volts to something suitable for your remote control. In addition to that you would need an electric cord and an arrangement to attach to the battery compartment of the remote. I don't recommend that you build this without supervision though because the wall outlet has lethal voltage in it.
I hope this helps.

Answer 6

The circuit draws as much current as it needs to. Current equals voltage divided by resistance. voltage is the power source and reistance is the resistance of the entire circuit.

With the remote question, stick to batteries. You would have to use a wall transformer that has an output voltage of 3 Volts (2 "AA" batteries).

This is because wall power is Alternating Current (120VAC at 60 Hertz), which means that the voltage goes up and down from 0-120 Volts at 60 times a second (Hertz).

The remote batteries are a constant 3 Volts, meaning it does not go up and down. To change from AC to DC and then voltage levels, means that you need a circuit to regulate the power. I included a link on how the wall transformer works.

Hope this helps!