Ole wifes tales

ok so a friend of mine leave radio, and A/C on never cutting them off.is that bad for battery when you start engine.

When you turn the ignition key to the “start” position, electricity is not initially running to the radio and A/C fan. Once the engine is running, then current is restored to those accessories. So, there is no difference whether you turn those accessories on immediately after starting the engine, or whether you have them in the “on” position prior to turning the ignition key.

However, this might vary, depending on the make of car. Traditionally, VW (for reasons that I could never understand) wired their radios so that they could be left on even when the ignition was shut off. Many VW owners learned, to their chagrin, that they could kill their battery as a result of VW’s…unique…design.

What make and model of car does your friend drive?

With today’s sophisticated electronics it would be easy for VW to include a 1 hour timeout on the radio.
But we have to accept what those crafty Germans hand down to us, and like it!

If I remember right there were a few domestic cars that the radio stayed on with the key removed, but that was cars from the 60s or earlier.

On all cars that I’m aware of the radio is only powered when in the RUN or Accessory Positions.
When you turn the key past RUN to the START possition, power is dedicated to the starter and spark production. You can see this easily by turning the key just a little past the RUN possition…not quite far enough to close the Starting circuit. Every unneeded accessory will lose power.
I also found out a trick that might come in handy for others.
One of our cars died and I spent half a day on a Sunday getting this car on a dolly and hauling it to my buddies shop, because I had no place to work on it.
I showed up in the morning to help and he hopped in the car and started it right up.
Turns out that in the START position there are two contacts. As you turn the key slightly from RUN to START there is the contact for the ingition (Spark) then farther you will close the contact for the starter motor. He started it and let the key off just a little which cut power to the starter curcuit, but left the ignition circuit still closed so the car would run.

The ignition switch was bad and no power was getting to the ignition circuit in the RUN position.
Had I started the car where it stalled and only release the key a little bit, I could have just driven it home.

I don’t know if all ignitions are this way, but it worked on that one.


If I remember right there were a few domestic cars that the radio stayed on with the key removed, but that was cars from the 60s or earlier.

Most of GMs cars/trucks today have a feature called Retained Accessory Power (RAP). RAP has been around for quite some time, at least back into the 2000s or earlier. RAP has a 5 minute timeout after the ignition is switched off and is immediately terminated upon door opening. RAP is one of the nice features I was glad to see included (along with automatic headlights) on my TBs…

I owned a couple of different GM vehicles that would turn the AC compressor while the car was starting. We learned to make sure the AC was off before we attempted to start the cars. These were vehicles from the 80’s and I haven’t seen that happen with vehicles of the last 20 years. Radios pull very little current so leaving them on wouldn’t affect starting the car at all.

You mean VW is still hooking up their radios that way? My '61 Beetle’s radio was hooked up that way.

RAP is one feature I like in GM cars. Even my Cobalts have it. I also like that the accessory outlets are powered even after the car is shut off an I leave the vehicle. It doesn’t happen often, but it is nice to charge my cell phone in a locked car while I’m out and about. I can go into the store and let the phone charge for a few minutes.

"You mean VW is still hooking up their radios that way? My '61 Beetle’s radio was hooked up that way. "

I honestly don’t know if they still do it that way, and that is why I said, “traditionally”.
My brother’s '64 Beetle was like that, as was my '71 Karmann Ghia, and I had a friend with an early Rabbit that was also wired like that.

Hopefully VW has changed their method of wiring the audio system, but…quien sabe?

From some of the postings about this on VW forums it appears that the radio will work for 1hr after you shut the key off at least on the 6th generation of the golf.

Unless you have a sound system that makes you a public nuisance everywhere you go, I can’t imagine a radio killing your battery overnight, especially not a transistorized radio using class B push pull final power amp turned up to reasonable volume levels.
The old tube radios, yea, they could definitely kill your battery.

AS others have said there is no power there yet while you’re cranking the engine.
Usually it’s just silly because it can be surprising to the next driver, or, moreover, circustances have change from the last time you turned it off.
A/C last night ( 80’ ) does not mean A/C this morning ( 55’ )

Here in the shop it’s a common prank to turn everything on ( wipers, signal, fan, radio, ) to surprise that next mechanic.

I don’t think leaving the radio/AC on all the time presents much of a problem for cranking or the battery. During cranking there’s usually a main relay that cuts off power to that stuff until the key is returned to the “on” position. And modern radios at normal sound levels use very little battery power anyway. I suppose a person could argue that it would be easier on the engine to let it warm up a couple minutes before introducing the add’l load of the AC compressor. It wouldn’t be something I’d lose much sleep over.

On some cars of the 1950s and earlier, if the radio is on when the starter is operated, the vibrator in the tube type radios could be damaged. My 1954 Buick had a warning in the owner’s manual to turn the radio off before starting the engine. There was no accessory or start position on the ignition switch in the Buicks manufactured through 1960. The ignition switch had three positions: Lock, On, Off. The radio always had power no matter what position the key was in. The starter was operated by stepping down on the accelerator and the starter would only operate when the key was in ON position. As soon as the engine started, the starter automatically turned off.
The 1947 Desoto my dad owned did have an accessory position and the radio would operate in either the accessory position or the on position. However, it wouldn’t operate if the ignition key was in the off position. The starter was operated by a push button on the dashboard.
On my 1947 Pontiac, the radio was wired through the ignition switch and I think there was an accessory position, but the starter was operated by stepping on a floor pedal and the starter could be activated whether the key was on or off.
My guess is that one was not supposed to have the radio on while one operated the starter which might damage the vibrator in the tube type radios and the starter was not activated through a start position on the ignition switch. Chrysler introduced the ignition switch with a start position to activate the starter in 1949. The other manufacturers soon followed suit. Personally, I prefer a starter activated by a floor pedal or a pushbutton on the dashboard.

On my 59 VW, the radio would be on regardless of the key position. You just got used to shutting it off when you stopped the car. Maybe the vibrator thing was the reason since the radio would usually be off when started unless you were parked listening to the radio.


The earliest of what we now call switchmode power supplies.
A metal reed is attached to two pairs of electrical contacts, similar to relay contacts.
A electromagnet coil moves the reed, which vibrated to alternately close each switch.
Nowadays transistors are used to make and break the connections, much faster: 20,000+ per second vs ~100 for the vibrator.

p.s. This schematic is missing a connection from the transformer secondary center tap to ground.

p.p.s. I got the owner of the website to correct the schematic error.

@circuitsmith: +1 Those were indeed the first switch mode power supplies, and nearly everything these days uses one (with transistors, not vibrators) including the battery chargers for the computers/tablets/phones we use to access this site. Really vibrators were a fairly ingenious solution for the need to generate a high voltage for B+ from DC power when transistors were not on the horizon yet.

Re. “RAP”, I think probably every car these days has something similar days–My 2006 Chrysler does this and you can set how long you wish the accessories to remain powered in a configuration menu, along with numerous other sundry adjustments.

I remember the 1960 Rambler my parents owned that had the factory radio which I think was manufactured by Motorola. This was a tube radio with no vibrator. The tubes had 12 volts on the plate and I suppose the voltage on the filaments was a lot less. I suppose this was a stop gap measure before transistors were used in the car radios, because my 1965 Rambler radio was completely transistor.

Triedaq My parent’s 1960 Rambler Custom that I ended up with was radio delete I’m surprised it had a heater!

The tubes had 12 volts on the plate and I suppose the voltage on the filaments was a lot less.

There’s no reason why the filament voltage would have to be less, on most vacuum tubes, the filament simply heated the cathode and was not a part of the electronic circuit. The filament or “heater” was electrically isolated from the cathode that it heated by a tube of mica or something similar.

I remember seeing an antique battery tube radio that did use tubes where the filament was the actual cathode. The strange thing about directly heated cathodes was the super quick warm up time, nearly like turning on a transistor radio it was so fast.