duel battery question

Submitted: Monday, Jun 09, 2003 at 12:49
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G'day, my question is, is it ok for my cd player to get its 12v through my aux. battery, and get it's earth on the main battery as it earths itself through the mounting bracket then on to the chasis. Even though my aux. battery earths on the block, i disconected the negative terminal on my main battery and my cd player stopped working. Which seams as if the two different negative terminals on my two batteries arn't electrically continuous, if that makes any sence! Can any 12v techie shed some light on my question please? Thanks Andrew..
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Reply By: Member - Martyn (WA) - Monday, Jun 09, 2003 at 21:56

Monday, Jun 09, 2003 at 21:56
Andrew,
I'm not a sparkie so there may be one out there who can be more help, as far as I'm concerned it sounds like yes you do have something amiss here, an easy check that I would do would be to earth the aux battery to the chassis / bodywork for a start. Where does your live come from? It must come as a completely separate line from your aux battery to the CD player, the problem may be the live and not the earth, another thing to try would be get a temp live from the aux battery and connect it directly to the cd player to confirm your live connection, if the CD works then disconnect the earth and see if the set goes off, this will conirm you earth connection theory. I would be looking more for a live type issue. You never know you may have been running your CD player off your main battery from the start.
As far as I'm aware you have to have an electrical circuit from positive to negative, on each battery, this is how I have all my accessories wired up and that's how the laws of electricity work, you won't get the live from one battery and the earth from another battery if I understand your question correctly. Hope this helps a bit.Keep the shiny side up
AnswerID: 22158

Reply By: Peter - Tuesday, Jun 10, 2003 at 08:06

Tuesday, Jun 10, 2003 at 08:06
A good test to see what is what
Use a 12v test lamp available for couple of dollars at care stores big w etc.
Put on to + of aux batt and check working on - aux batt
probe to earth/body on car.
If it lights then you have a connection to car.
I would also suggest checking aux batt is correctly earthed.

Second see where cd is getting power.
Isolate aux batt (Disconnect) and see if the power is still there
connect test to car earth and probe the power lead of cd to see if there is power .

AnswerID: 22174

Reply By: Smithy - Tuesday, Jun 10, 2003 at 12:15

Tuesday, Jun 10, 2003 at 12:15
Andrew,
Be real careful. If the batteries anen't connected in parrallel and you have the CD player linking the two, you could short out and blow you're CD player. (Once the aux battery goes flat it becomes a dead short and will draw high current from your main batt through your CD player (which it's not rated for).
Like the other guys have posted, do the checks and I suggest you don't put it off (well if you don't think you need a new CD player and can con the misses into a new one, well, then it becomes another matter)
Cheers and Good Luck.
Shift Sparky
AnswerID: 22191

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