Explain the function of the relay in a vehicle?
I know theoretically how a relay works and I know about a magnetic coil, armature, working current, control current, working current contact, etc. But ultimately I don't understand how a relay works in a car.
Especially after the statement: The advantage of a relay is that you can switch large currents with it??? How large currents in a car? The relay is also tied to the 12-volt battery, and I can't switch more than 12 volts, not even with a relay.
So if I now control my window heating with a switch, the current will be too high for the switch, and it will probably burn out or something. What about the relay? Where do I get the power for the control circuit, and where does the power for the operating circuit come from?
Where do 2 different separate power sources come from as circled in the picture???
Can someone explain this in detail and clearly? Like I said, I can explain it theoretically, but I have no idea how it actually works.
(I didn't pay attention to spelling because I wanted to do it quickly)
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I just answered another question where I described how it works:
You confuse current (A) with voltage (V)
A classic relay has the following parameters:
Control circuit (coil side, brown circle in your drawing):
Load circuit (blue circle):
Different parameters often apply to both circuits, for AC and DC. For AC on the load side, additional restrictions often apply for non-resistive loads. Many relays are also only suitable for one type of current in each circuit.
But all of this is written on the relay itself or noted in the datasheet. You have to choose a relay that's suitable for your application.
Your statement is correct, for example, if a relay is controlled with 12V/0.1A but switches a load of 12V/5A.
This is to clarify that there are two independent circuits—the control circuit and the load circuit. The image serves to illustrate how a relay basically works.
There are also cases where a relay with a 12V DC control circuit switches 230V AC mains voltage on the load side.
But it doesn't have to be that way. Both circuits can, of course, be powered from the same source, share a common ground, and also be powered from the same source—as in your application.
And then there's the really big relay: the contactor. On the load side, high voltages and high currents are involved. In other words: high voltage. Contactors can also be equipped with a coil designed for low voltage. A mere 12V can then switch a really powerful 400V three-phase machine. 🙂
Simple automotive relays without special functions are essentially identical to "regular" relays. They are simply designed for the needs of the automotive power system and conform to certain standards regarding connections, etc.
A relay CAN switch high currents, but that is not the essential property of a relay on which everything depends.
You must not confuse current with voltage.
Voltage is 12 volts, current is what flows when voltage is applied. The more power something consumes, the more current flows. The relay coil requires very little current—just a few milliamperes. However, the relay can switch loads that require many amperes.
Okay, my mistake. What are the two power sources shown in the picture? Does the same amount of current reach the consumer as there is at the beginning of the control circuit? I don't think so. What does the relay do that, once I have a supply voltage for the circuit, allows me to switch large currents at the end, for example, for windshield heating or the starter?
A current flows through the solenoid coil, which depends only on the applied voltage and the coil's resistance. This current has nothing to do with the current being switched. It doesn't matter whether you're switching a 10-watt light bulb or a 20-watt one, even if it's burned out and no current flows at all. One side of the relay has nothing to do with the other.
Hi,
Actually, you've already figured it out quite well yourself. The batteries in the circuit diagram are your car batteries.
The relay with the sink only requires a small amount of power, meaning a small amount of current. The switch in the dashboard can easily handle this. The switch in the relay has significantly thicker contacts, allowing it to switch a larger current.
Hello
The power always comes from the same battery. If you use a switch to turn on the windshield heater, you need a powerful switch.
If you switch on the window heating via a relay, a weak switch is sufficient to activate the relay. The window heating is then switched on via the relay's strong contact.
Greetings HobbyTfz