Question for our in-house ICE-men (women welcome too)... I've run a big power cable from battery to boot and are going to hook up an mp3 player to it (see separate threads for that), but because it is not hooked up to the accessory position on the ignition, it will always be under power. I dread the day I forget to switch the mp3 player off and it runs my battery dry :eek: !

Would it be possible to incorporate some sort of automatic switch (or even use the accessory switch itself) as to have it automatically switch off the power to the mp3 player when I remove the key out of the ignition?

Q.

I shouldn't imagine an MP3 player will use all that much power, so unless you're leaving the car a few days you should be alright...

Not sure on how to wire it to the accessory switch, unless the MP3 player has an input for this, or the power was connected in serial from the head unit - I'd imagine neither of these are the case.

As for an automatic switch - on my fridge I have a 12v socket splitter (tenner from Halfords), which incorporates a cut off, so if the voltage from the battery drops beneath 10.8V it'll stop the accessories connected to it drawing power. Maybe you could cannibalise one of these, or find out how they work?

Rob.

That might actually be the solution, put one of those 12V socket splitters in between. Or (and I'm just making this up as I go along) could there be a point on the battery (as there is a little small distribution block on top of it already) which contains the accessory switch power? Big k?

Q,

Most after-market head units feature a "remote" wire - this carries 5v when the head unit is turned on. Typically it connects to an in-car amplifier to 'switch it on' when you start listening to the head unit.

I'm sure I've seen remote switching units that use the remote feed as an input to switch a relay, and thus supply power to everything only when needed...

The accessory feed wire is 12v in itself....

I've done the same, used a permanent 12v from the boot power socket. Forgot to turn the mp3 player off once, didn't do anything to my battery.

The mstation *really* doesn't like power blips tho, so I would try and stay with a perm feed and on \ off direct.

Think the standard battery is rated at 60/70 Ah, so it would take a while for it to drain off an MP3 player!

Rob.

Stimps, that sounds more like a 'proper' solution which I'm duly going to investigate

Rob, ofcourse it would take some time, but as Murphy's Law dictates, if anything can go wrong, it will

Q.

Oh, and Ian, what would cause power blips? Starting the engine for instance?

Originally posted by Tavia4x4 in this post

The mstation *really* doesn't like power blips tho, so I would try and stay with a perm feed and on \ off direct.

If you had a nice fat capacitor somewhere that would help to smooth any blips in the power...

Originally posted by Quinten in this post

Stimps, that sounds more like a 'proper' solution which I'm duly going to investigate

Rob, ofcourse it would take some time, but as Murphy's Law dictates, if anything can go wrong, it will

Q.

Oh, and Ian, what would cause power blips? Starting the engine for instance?

Are you sure it's Murphy's Law, not Ohm's Law?

Originally posted by KLB in this post

Are you sure it's Murphy's Law, not Ohm's Law?

Now your being "resistive".

Andy

I feel a right Henry, 'cause I don't know Watt you're talking about.

A case of being 'ampered by lack of knowledge?

FYI left the car fridge in my mums 3 series overnight and it pancaked the batt wouldnt even unlock...

It would do as the current drawn by those fridges is quite a bit so without the engine running it will run down.

I think this thread is "volting" around too much and needs some impeidance, although the "current" direction could be polarised, and take it "farad farad" away from the dribble I,m spouting.

Andy................sculking

Yeah, those fridges draw a lot of current, I reckon it could kill the battery in as little as 2-3 hours. Hence why I invested in the "cut off" splitter, so as not to have to make an embarrassed call to the AA!

Insulates quite well though, so holds the temperature for about 8 hours, which is nice...

Rob.

Doesn't the 12v socket in the boot have some kind of time out on it several hours with ignition off, or am I mistaken?

It might well do, though some of us don't have 12v sockets in the boot anyway...

Rob.

ah rob you must have the "sports" model not the agricultural spec product?

Well, it certainly looks like a Coupe, albeit an American one...

Rob.