Outer Limits 4x4 Board

hi wired up a subwoofer and amp into my mq patrol it has dual battries so i ran the main power off the aux battery and now the car will not start it will spark at the negitive terminal untill i turn the key to acc what should i do? by the way it is a 24volt system

What do you mean "spark at the negative terminal"? That implies the terminal isn't tight! Try tightening it?

Scott

If it is a 24 volt system, then you dont have an "auxilliary" battery, unless you have a total of 4 batteries.

If you have placed your amp earth wire at the midpoint of the two batteries (the -ve of your "auxilliary" battery, also the +ve of the lower battery) and tied the chassis of the amp direct to the chassis of the vehicle you have placed a dead short across your lower battery.

No disrespect, but it may be worth leaving the installation to someone that knows how to wire it up correctly, as you could make a hell of a lot of costly mistakes before you are finished (more than the cost of getting it done properly).

As it stands it sounds like you have trashed one battery (start off by removing your amp, and get the lower battery recharged), and may well have inadvertantly given the amp too much voltage (24v instead of 12v).

If I understand what you're saying..., you have a 24V MQ... which means you don't HAVE an auxiliary battery, you have two batteries that form a 24V system.

It sounds like you are trying to pick up earth from the second battery, but that is actually meant to sit at +12V, so it sparks when you try to connect it to earth as well..?

The way your two batteries work (let's call them B1 and B2) is, in simple terms, that B1 does 0 to 12V, and B2 does 12 - 24V.

So you can't get 0 (ground) off B2.

Anyway, you're asking for trouble if you try to run 12V stuff off one battery of a 24V system.

-Scott- wrote:What do you mean "spark at the negative terminal"? That implies the terminal isn't tight! Try tightening it?

Scott

Strapping the mid point of the 2 batteries to the chassis?????? (via earth wire of the amp and chassis earth of the amp).

yeh i have done great systems on normal cars and normal 4wd's its just this mq i am having trouble with gonna get an auto elec to look at over weekend

my shityhouse diagram of what makes 2 12v batterys in 24v by the way they call it a series circuit
parrell circuit is where both + are jonined together to increse amp but not volt the wiring diagram will produce 24v at same amount of amps as per each 12volt battery only thing that changes is the voltage **trade school what a long time ago i might be wrong**



think about what ur + is going to ur ground should goto the ground
u might just have to find 24volt to 12volt converter thats all i can think of but it makes sence ....how do headunits wire up u got memory swtich active and gnd memort is cont to the battery and swich acitve is via iggy switch

if you can wire up car sterio systems into cars perfect 100% all the time im sure you can work this out on your own

cheers justin

Hi 40 year old electronic engineer from the UK here.

Heres what you do. You run the entire stereo system from the battery that has its negative terminal connected to the chassis. The positive power supply to the stereo you pick up from the point where the 2 batteries are joined together and the negative feed to the stereo you pick up from the chassis.

Your mistake was running the stereo from the wrong battery and in doing so shorting one of the batterys out through the stereo. hey you had a 50/50 chance.

Don't be suprised if the stereo has died from shock.

JulesUK wrote:Hi 40 year old electronic engineer from the UK here.

Heres what you do. You run the entire stereo system from the battery that has its negative terminal connected to the chassis. The positive power supply to the stereo you pick up from the point where the 2 batteries are joined together and the negative feed to the stereo you pick up from the chassis.

In theory this is fine, but in practice it kills batteries because the less-utilised battery is preferentially charged by the charging system. Thus the more utilised battery dies. I never used to believe this either but I have seen it covered too many times now.

Jason

Mmmm. Never come accross this and don't understand why that should be the case (although if youve experienced it then who am I to argue)

The thing is as a lead acid battery becomes more discharged its internal impedance goes up. If you have 2 batteries in series then the proportion of the charge voltage accross each of the batteries is proportional to the battery impedence. When the 2 batteies have the same impedence the charge is shared equally, when one of them has a higher impedence (coz its flatter due to stereo use) then the charge voltage accross it would increase thus charging it more than the other battery until their impedences became the same again (back to equal charge). So in theory the whole thing is self regulating and both batteries always seek to be at the same level of charge as each other.

JulesUK wrote:Mmmm. Never come accross this and don't understand why that should be the case (although if youve experienced it then who am I to argue)

I haven't experienced it myself, and it never really made a lot of sense to me either, but there are many reports of it.

Here is a discussion of it:

http://www.a1.nl/phomepag/markerink/12v&24v.htm

I think the crux might be this quote:

To put it simply:

Every amp that is drawn off the 'downstream' battery has to come THRU
the upstream battery. This will dramatically overcharge the upstream
battery if you're feeding much current from the 'downstream' 12V battery.


Essentially, you'll smoke the upstream battery with serious overcharge.

I can see picking off some tiny loads like a CB that is mostly on receive
but not much more.

I am installing a DC-DC converter in my unimog to get 12V from 24V.
It can cover up to about 16 A though they are available in higher
ratings. Not for a winch though!

I guess it's a matter for each person to decide, but I've read about it too many times to bother trying it with my car (if I had a 24V car...)

Jason

Batteries aren't recharged by voltage, they're recharged by current. Well, actually they're recharged by charge - who would have thought? Charge is measured in coulombs; current is the flow of charge - literally, coulombs per second. Voltage is the amount of energy per coulomb, and is independent of the number of coulombs.

If batteries are connected in series and charged as one bank, both batteries are receiving the same charge current. If they have been discharged to different depths they require different amounts of charge - but, being fed the same current, they are receiving the same charge.

So, if one battery delivers more charge than the other, but both receive the same amount from the charging system, the "lower" battery is rarely fully charged, and the upper battery is regularly overcharged.

Don't do it.

Scott (BEng Electronics. )