what is the purpose of having a relay im car starters?

Question

automotive

Answer 1

The starter draws a couple hundred amps. If you passed all that through the ignition switch, you'd have to have a massive switch and huge wires. Pre solenoid vehicles usually had a foot switch to start the engine.

Answer 2

First you need to fully charge the battery with a self leveling battery charger @ 2 amps for up to 6 hours. An inexpensive hand held multi-tester which includes a volt meter is needed for a couple of tests which you can do. Check the battery voltage. It should read a bare minimum of 12.25 volts *after the battery been charged and has sat overnight for at least 12 hours. Anything less than 12 volts, you'll have trouble trying to start the car. If the battery is older than 3 years it may be in trouble. 12 volt batteries can drop off voltage because of one of the 6 aging or dead cells. Make sure the cables are clean dry and tight on each end. particularly the ground to frame and the positive at the starter solenoid. When you get the car started with the battery or heavy duty jumper cables use the volt meter connected to the battery to check the alternator output. The meter should read between 13.5 -14.0 volts. This tells you that the alternator is charging properly. If you aren't getting at least 13.5 volts with the motor running the alternator needs replacement. A fully charged new battery should read 12.85 volts

Answer 3

The starter motor draws a lot of current. The contacts on the relay are capable of handling all of the current. All you have to do is turn the key switch and the car will start. Without the relay, it would take a lot of force to energize the contacts.
So it is for safety, and convenience.

Answer 4

So that the starter switch does not have to carry the very heavy current needed to operate the starter motor.