Car Stereo - Making Battery go flat - how to figure out whats going on

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Jaxson

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#1358231 3-Aug-2015 21:56

jpoc:
Jaxson: Are you sure you've got the ACC setup right?

Can you use the stereo with the key right out of the ignition?

Without the key, the stereo should be essentially completely off.

I believe that all variants of the ISO connector have one pin that is always live irrespective of the position of the ignition key.

When they key is out, the radio is still allowed to draw current to maintain the clock and other functions such as preset frequencies for the tuner etc.

Yes but if you get this wrong the head unit will be fully powered up constantly.
Hence the simple test of 'Does it work with the key out'?...

dickytim

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#1358291 4-Aug-2015 06:37

jpoc:
Jaxson: Are you sure you've got the ACC setup right?

Can you use the stereo with the key right out of the ignition?

Without the key, the stereo should be essentially completely off.

I believe that all variants of the ISO connector have one pin that is always live irrespective of the position of the ignition key.

When they key is out, the radio is still allowed to draw current to maintain the clock and other functions such as preset frequencies for the tuner etc.

This is correct, but some connectors have this pin and the acc pin around the wrong way for the car. I have seen this with Commodores so it may be with others as well.

Like someone else has said can you turn the stereo on when the key is out?

nakedmolerat

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#1358299 4-Aug-2015 07:29

Talkiet:
shk292:

REMOVE YOUR WATCH FIRST. Car batteries are big enough to kill you. If done correctly it's safe but there's a staggering amount of energy in them.

Cheers - N

Maybe if someone drops one on your head from a great height, but there is no way that 12v dc is going to push enough current through your body to kill you

Fair enough I guess... But it could weld a metal watch to your arm still :-)

But yeah, you're right - pure electrocution won't kill you*

Cheers - N

*Probably, YMMV

It's a myth, you can't die from electrocution from a 12v battery.

The danger actually come from battery explosion when you ignited the hydrogen gas.

Morgenmuffel

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#1362700 11-Aug-2015 11:22

Ok i'm back

with the stereo disconnected it still goes flat, just not as fast.

Turning off the ignition did turn off the stereo (I think, i'll double check that)

I did notice that when wiring it up while doing some testing I forgot to disconnect the battery and there was a good spark when I touched the earthing wire of the iso connector to the car frame, the old Stereo didn't have an earthing wire so far as i can tell.

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wellygary

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#1362743 11-Aug-2015 11:52

Morgenmuffel: Ok i'm back

with the stereo disconnected it still goes flat, just not as fast.

Get the battery tested, the source of your troubles is not the stereo, but ruling out the battery is your best first step....

trig42

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#1362744 11-Aug-2015 11:53

Sounds like you need a new battery then.

If that goes flat, something else is drawing too much power, and an auto sparky should be your next stop.

richms

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#1362830 11-Aug-2015 13:31

Test the load on it with a battery.

If the 2 power leads on the stereo are the wrong way around it wont work with the key out, it will instead shut off and lose the clock and settings when you take the key out. Also means that the stereo is being powered off the wrong wire so may blow that fuse.

Issues are often that the powered amplifiers in the car if they are fitted are not shutting off. Seems that the trigger wire on some of them is over sensitive and they can run all the time. Often there is a pathetic amplifier closer to the rear speakers that runs off the speaker out from the head deck and will do bi-amping etc. If that amp is left on then it will be flat in a couple of days.

Richard rich.ms

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ZollyMonsta

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#1362847 11-Aug-2015 13:52

I had this exact same issue in our Mitsubishi 380 a fortnight ago. took out the stock stereo and put in a LCD/DVD Headunit. The battery went flat twice.
Suspect battery was near end of life and the new stereo also drawing more current than previously (I also used ISO connectors to existing wiring).

Old battery was also probaby underpowered for our V6 rated at 400CCA. The new battery is a 530CCA rated one. Still going fine after a week and no issues.

So as others have said I would say its near end of life battery plus probably under-rated.

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TonyR1973

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#1399142 2-Oct-2015 22:00

nakedmolerat: It's a myth, you can't die from electrocution from a 12v battery.

Yep. There's an disturbing level of ignorance of basic science principles in this place for somewhere that's called "geekzone". I guess that's what happens when the populace is convinced that ownership of a "smart" phone somehow makes them technology gods.

TonyR1973

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#1399146 2-Oct-2015 22:10

ZollyMonsta: Old battery was also probaby underpowered for our V6 rated at 400CCA. The new battery is a 530CCA rated one.

If it was starting it comfortably, it wasn't underrated. 400CCA will happily do a 3.5L V6 and if you find it going flat while cranking, some engine maintenance is in order.

CCA is not a good indicator of reserve capacity either, in the case you're looking for a starting battery to abuse with low current, long duration draw like running a stereo with the engine off.

richms

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#1399152 2-Oct-2015 22:28

Also specified CCA for the car is for northen US/canada winter type starting and allows for some aging of it. Can go way way under in NZ and it will be fine for years.

Richard rich.ms

Rikkitic

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#1399219 3-Oct-2015 09:24

1. Could this be a simple short-circuit? Both power leads from the head unit ultimately connect to the same place, one just goes through the ignition switch. If that is bypassed the unit will draw extra current all the time.
2. Since this IS Geekzone maybe a brief explanation of why car batteries cannot electrocute you is in order instead of just ragging on someone's ignorance. I=E/R, in other words, 12 volts is not enough to overcome the resistance of your body. Not sure where the cut-off is, depends on circumstances, but I would think around at least 80 or 90 volts would be needed to do the trick. The current from the battery can kill you many times over, but only if the voltage is high enough to push it through you. Watch out for inverters. That will do the trick.

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