Why do modern cars silence the radio when starting?

Factual Questions
1

My company have given me a new car. It’s a Hyundai i40, and it’s very nice, thank you.

When you get into the car and turn the ignition key to start the car, it cuts the radio.

It also has a feature that I’ve seen in other new cars. When you stop moving forward and put the car into neutral (it’s a manual, btw), it stops the engine. The engine then restarts when you put your foot on the clutch. This action does not cut the radio.

I always understood that the reason the radio gets cut during ignition is that the action of the ignition coils produced so much EM interference that your radio would produce a loud burst of static, so it cuts the power to it during this to prevent that. But I can start my shiny new car at the lights every time without any static issues.

Was I wrong? Is there some other reason to cut the radio during the initial startup, but not subsequent restarts?
((if you stall the car, it will also restart the engine gracefully without a key turn, and without cutting the radio))

2

The “accessory” position in the ignition key thing is usually “back” - starting is “forward”

So - “accessory -> off -> start” -

The process of starting the car is not (necessarily) silencing your radio - it is the action of changing the position of that ignition switch. (You’re turning the accessories off on the way to starting the car).

The other methods that start your car that you mentioned are bypassing the ignition switch - but I am sure they rely on that swtich being in teh “on” position.

3

The radio, and some other things that draw power, get cut off so as not to draw from the battery. When the car has been sitting and the engine is cold, it’s a much bigger draw on the battery to start the car. Does the radio have either a power antenna, or a CD player? those can draw a lot. It probably shuts off power to the accessory plug (what used to be called the cigarette lighter, but it doesn’t come with the heating plug anymore) as well, so if you have a GPS, or iPod or something plugged in, power is momentarily interrupted, but you don’t notice, since they have some battery storage capacity.

I don’t know how automatic starts work, but probably with capacitors and relays that prevent the car from truly stalling in the first place. It probably doesn’t have to “turn over” again, because you stall the clutch, but you don’t lose the fuel or electrical system, since it is all controlled by a computer, and not a mechanical system.

Now, I don’t know for sure, I haven’t looked it up-- but I was an Army mechanic for 8 years.

4

Just a guess: so all available battery power goes to the starter that way?

5

That used to be the claimed rationale years ago. When you turned the key to the “start” position, they would cut power to damn near everything else in the car: radio, headlights, HVAC blower, and so on.

My previous motorcycle even had an official “load-shedding relay” that cut power to all your accessories when you pushed the start button.

My current car (2013 G37) does not require a mechanical key: you momentarily tap a button on the dashboard (without holding the clutch to the floor) to power up all the accessories. To start the engine, you hold the clutch to the floor while you momentarily tap that same button. The car then kills all the accessories (except the headlights :confused:) and starts the engine, then restarts all the accessories.

I don’t understand why the headlights on my car aren’t part of this load-shedding routine, especially since that was the case on older cars.

If by “ignition coils” you mean the coils used to drive the spark plugs, note that these are firing whenever the engine is running; if they were problematic during a start, then they’d be a problem any time the engine is running.

In looking at the Wikipedia page for the i40, it appears not to be a hybrid drivetrain, so your engine is probably equipped with a conventional starter motor and 12-volt battery that gets used during manual cold-starts and automatic restarts.

My theory is this:

-During the initial start, the engine and battery are cold; the starter needs all the current it can get so that it can crank the engine through that cold viscous oil. Moreover, since you’ve just gotten into the car, the assumption is that you haven’t been listening to your favorite song for the past two minutes, so you won’t mind if the radio gets interrupted.

-During automatic restarts, the engine is warmed up, so the oil is at a nice low viscosity. It doesn’t take quite as much current to crank it, so it’s not quite so critical to shut off all the accessories. Moreover, if it’s an automatic restart, and the radio is on, then the assumption is that you’ve been listening to it and won’t be happy if your favorite song gets interrupted. So it keeps the radio on.

6

That’s most of it.

The other reason is that the voltage swings rather wildly during starting, especially if the starter is cranking hard on a cold day. It’s a lot kinder to the car’s various electronic bits to wait until the car’s voltage has stabilized before turning everything on.

7

This feature is becoming increasingly common. It is designed to reduce the pollution from the exhausts of idling cars, and thus help the manufacturers meet their targets. It also saves fuel.

They will have beefed up the starter motor and the alternator to make sure that the battery doesn’t run flat in prolonged stop/start conditions. If the voltage drops enough, the device will stop working.

8

While the principle is sound, I’m not sure that’s true. I had an old VW cabriolet in college with an aftermarket CD player. I was annoyed that the radio would turn off when I shut the car off, so I ran a direct line from the battery to the radio and amps. It worked great and the cdplayer didn’t skip at all when I started the car. I could leave it for a week in the cold with same results. The only drawback was if I forgot to shut the stereo off = dead battery.

I think the reason the radio shuts off when starting is bored engineers plotting to annoy us.

9

Which only demonstrates that the singular form of the word “evidence” is not “anecdote”. For your CD player, your battery, and your starter, the voltage sag from powering the starter weren’t enough to glitch the stereo. That’s not guaranteed universally, and I know of at least one car stereo I’ve installed the same way as you describe which would reset when I cranked the car.

With modern computerized vehicular infotainmmication* systems, I bet their power needs are more refined and delicate than any $200 aftermarket head unit from 10 years ago.

And that explains the RATIONAL reason to wire the stereo to the switched accessory circuit: if it’s too easy to kill the battery overnight by simple forgetfulness of a minor accessory, it’s a bug that has to be fixed.

That doesn’t explain why headlights seem to be exempt from this (in older cars)… maybe someone made an engineering decision that having headlights on would be useful and valuable even with the ignition switched entirely off. I don’t know the number of jump-starts I’ve needed because of that feature.

*I just made that word up. Portmanteau of “information, entertainment, communication”. Pretty much every Bluetooth-enabled in-dash computer/stereo/speakerphone system made in the last 5 years.

10

You are all over-thinking this. Whoever came up with this wonderful feature obviously shares their car with a teen-ager, and was sick and tired of being blasted out of their skull because the kid left the volume as high as it would go. :eek:

11

Some of the auto-stop/start systems keep track of / control piston position on shutdown and use this information to restart the engine by resuming the ignition sequence at the appropriate cylinder - without using the starter at all. http://www.caranddriver.com/features/engine-stop-start-systems-explained-tech-dept

Another consideration is that when the engine is being restarted shortly after a stop, the engine is known to warmed up, the oil is flowing, etc. It can be assumed that the starter load will be much less than a worst-case initial cold start and so maybe disconnecting all the other accessories during restart isn’t necessary.

12

Not on any car I can remember driving in the last 30-some years. It’s always off -> accessory -> run -> start.

(With “accessory” and “run” perhaps being one position or perhaps two separate positions.)

I vaguely kinda-sorta recall that accessory might have been on the other side of off, on some 60’s-or- 70’s-era car that I drove.

13

I thought that’s just in case your car breaks down and you abandon it, it’s better to have the headlights on so it’s more visible by the side of the road.

14

Bunch of kids in here.
Insert key = off
Turn key back = ass
1st position fwd = run
2nd position fwd = start

I still have 2 vehicles like this.
Got to go almost back to starter buttons on the floor to find one different.

Got to know your stuff to start an older car with the start button under the gas pedal. Mostly when it was a hot engine on a hot day. Bawahahaha

Whipper snappers, get off my lawn… :smiley:

15

If you abandon your car with the headlights on, you’ll come back to a dead battery (along with whatever problem compelled you to abandon it in the first place).

16

And that’s pretty much all of it, AFAIK. It’s called “prove out” in some older manuals and writing guides, I don’t know why.

17

If it’s serious enough to make you abandon, a dead battery is the least of your worries. Also, headlights on is optional. Better to replace a battery (unlikely, a charge is probably enough) than have your car totaled.

18

The radio still comes on, just a second or two later, when the car is running.

19

Machine Elf is it the headlights or the daytime running lights that stay on during crank? A lot of DRLs draw a bunch less current than headlights (particularly LEDs)
As far as the radio being turned off getting max power to the engine is something that was done for years and years.
Back in the day (remember Gus?) cars with points had a resistor in the ignition circuit so the points didn’t run at full system voltage. This made the points last longer. During crank this ballast resistor was bypassed so the points got full available voltage.
As cars electrical systems got more sophisticated it became possible (and easy) to shed loads by turning off extraneous stuff during crank. From an engineering standpoint there is no advantage to leaving the radio/ heater fan/ AC compressor etc on during crank. Turning them off is as easy as cutting the power to one relay, and cutting them off just might allow a car with a bad battery to start, where leaving them on would strand you.

20

You bet I do.
And I used to change points, condenser , dist. cap & plugs about every 3rd oil change if I wanted to keep her singing the way I liked.

I loved being the hare… < VEG >