How a Toaster Works How Does a Toaster Toaster?
For most Americans That said, a toaster is a must-have tool for everyday cooking. A toaster may seem like a simple device, but it still raises the question: how exactly does a toaster bake bread? How do the various settings work? How does a toaster know when to pop a slice of bread?
How a toaster works
Next, we will dissect a common pop-up toaster to answer All the questions above and a few others!
In the US, you can buy a toaster for less than $20 at any budget store. The model shown on the right allows you to set how much the slices are toasted, and also has a defrost mode.
The fundamentals of any toaster application are simple. Toasters use infrared radiation to heat slices of bread (see How Thermos Works for information on infrared radiation). When you put in the bread and see the coil turn red, that’s the coil producing infrared radiation that gradually dries and chars the surface of the bread.
The most common method for toasters to generate infrared radiation is to use nichrome wire wrapped around a mica sheet, as shown:
Nichrome Iron alloy wire is an alloy of nickel and chromium. It makes a good heat generator because it has two characteristics:
Compared to materials such as copper wire, Inconel wire has a fairly high electrical resistance, and even a short length of wire has enough heat to generate The resistance.
Inconel does not oxidize when heated. Iron wire corrodes quickly in the heat inside a toaster.
The simplest toaster requires two mica sheets wrapped around Inconel wire, placed parallel to form a slot about 2.5 cm in between, the Inconel wire is directly connected to the plug
If you want to toast:
You want to put a slice of bread in the slot.
1. Then you need to plug in the toaster and observe the condition of the bread.
2. When the bread is brown enough, you unplug the toaster.
3. Then you have to turn the toaster upside down and take the toast out!
4. Most people don’t have that kind of patience and don’t want the table covered with crumbs. So usually the toaster has two other devices:
5. A spring loaded tray. For popping toast. This way you don’t have to turn the toaster upside down.
6. Timer. Used to automatically turn off the toaster and release the tray at the same time to pop the toast.
The photo below shows a top view of a slot in a common toaster. Two mica and inconel plates are lined up on either side of the slot. There is a liftable metal bracket in the slot for lifting and lowering the slices of bread.
Many toasters have a pair of grates on either side of the slot to hold the slices of bread centered. This short video was taken from the bottom of the slot and shows how the grate is activated. As the bracket approaches the bottom of the slot, it pushes on two metal springs, pulling the grate inward.
A bracket in each slot is attached to a handle, which can be pressed to drop a slice of bread into the toaster, as shown below:
When you press the handle, three conditions must be present:
1. There must be some means of holding the handle so that the toast stays in the toaster for a certain amount of time .
2. Need to energize the Nichrome wire.
3. There must be some kind of timer to release the tray at the right time for the slice to pop out.
In this toaster, both the grip and the power switch are part of the handle:
In the image above you can see a plastic rod and a piece of metal attached to the handle. The plastic rod presses against a pair of contacts on the circuit board to energize the nichrome wire, while the metal piece is attracted by the electromagnet, keeping the toast below. You can see the contact (copper on the right) and electromagnet (green lump on the left) in the following images:
The two photos below show the plastic rod How to power up a toaster. In the first photo we used a pencil to simulate the plastic rod and you can see how it separates the contacts:
This toaster works like this:
When you push down on the handle, the plastic lever presses against the contacts, causing the The circuit board is powered up.
The current flows directly through the contacts into the Inconel wire, which starts toasting.
A simple circuit consisting of a transistor, resistor, and capacitor turns on, energizing the electromagnet.
The electromagnet attracts the metal tab on the handle, keeping the bread in the toaster.
A simple circuit acts as a timer. The capacitor is charged through a resistor, and when it reaches a certain voltage, it cuts off the current to the electromagnet. The spring pops both slices of bread at once.
Meanwhile, the plastic rod rises, cutting power to the toaster.
In this type of toaster, the element that controls the degree of scorching is simply a variable resistor. Changing the resistance changes the speed at which the capacitor charges, thus controlling how long the timer waits before releasing the electromagnet.
Simpler toasters use a bimetal (see How Thermometers Work for details on bimetals) to turn off the electromagnet. The temperature in the toaster rises, and when the sheet of metal is heated, it bends, eventually activating a switch that cuts power to the electromagnet. There are two problems with the bimetal method:
If it’s cold in the kitchen, the first slice of toast will be more charred than usual.
If you want to bake a second batch of toast, the toaster will be too tender because the toaster is already hot.
The electronics in this toaster make the toaster a lot more even!
